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Title: Natural History of Cottonmouth Moccasin, Agkistrodon piscovorus (Reptilia)
Author: Burkett, Ray D.
Language: English
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=================================
UNIVERSITY OF KANSAS PUBLICATIONS
MUSEUM OF NATURAL HISTORY
Vol. 17, No. 9, pp. 435-491, 7 figures in text
------------ October 27, 1966 ----------------
Natural History of Cottonmouth Moccasin,
Agkistrodon piscivorus (Reptilia)
BY
RAY D. BURKETT
UNIVERSITY OF KANSAS
LAWRENCE
1966
UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY
Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
Frank B. Cross
Volume 17, No. 9, pp. 435-491, 7 figures in text
Published October 27, 1966
UNIVERSITY OF KANSAS
Lawrence, Kansas
PRINTED BY
ROBERT R. (BOB) SANDERS, STATE PRINTER
TOPEKA, KANSAS
1966
[Illustration: Printer's Logo]
31-4629
Natural History of Cottonmouth Moccasin,
Agkistrodon piscivorus (Reptilia)
BY RAY D. BURKETT
CONTENTS
PAGE
INTRODUCTION 439
ACKNOWLEDGMENTS 440
SYSTEMATIC RELATIONSHIPS AND DISTRIBUTION 441
DESCRIPTION 444
Color and Pattern 444
Scutellation 444
Dentition 449
HABITAT AND LIMITING FACTORS 450
REPRODUCTION 452
Courtship and Mating 452
Reproductive Cycles 452
Embryonic Development 454
Birth of Young 454
Number of Young per Litter 454
Population Composition 455
Reproductive Potential 455
GROWTH AND DEVELOPMENT 456
Size at Birth and Early Growth 456
The Umbilical Scar 457
Later Growth and Bodily Proportions 457
SHEDDING 459
The Shedding Operation 459
Frequency of Shedding 460
FOOD HABITS 461
Methods of Obtaining Prey 461
Food and Food Preferences 462
MORTALITY FACTORS 465
Natural Enemies and Predators 465
Parasites and Diseases 465
Miscellaneous Causes of Death 466
BEHAVIOR 466
Annual and Diel Cycles of Activity 466
Basking 469
Coiling 469
Locomotion 470
Disposition 470
Defense and Escape 471
"Head Bobbing" 471
Combat Dance 472
THE VENOM 473
Properties of the Venom 473
Venom Yield and Toxicity 473
Susceptibility of Snakes 475
THE BITE 476
Effects of the Bite 476
Treatment 477
Case History of a Bite 479
Snakebite in the United States 480
SUMMARY 480
LITERATURE CITED 485
INTRODUCTION
Objectives of the study here reported on were to: (1) learn as much as
possible concerning the natural history and economic importance of the
cottonmouth; (2) determine what factors limit its geographic
distribution; (3) determine the role of the cottonmouth in its
ecological community; and (4) compare the cottonmouth's life history
with that of other crotalid snakes, especially the kinds that are most
closely related to it.
Twenty-five live cottonmouths were kept in the laboratory for the
purpose of studying behavior and fang shedding and for comparison of
measurements with those of preserved specimens. Live snakes were
obtained in Brazoria and Nacogdoches counties, Texas, from Hermann Park
Zoo, Houston, Texas, and from the late Paul Anderson of Independence,
Missouri. Preserved western cottonmouths were examined for the purpose
of determining variation, distribution, food habits, body proportions,
embryonic development, and reproductive cycles. The cottonmouths
examined include: 221 from Texas; 33 from Arkansas; 22 from Louisiana; 2
from Illinois; and 1 each from Kansas, Mississippi, and Oklahoma.
In the preparation of this report I have examined all available
literature pertaining to the cottonmouth and have drawn from these
sources for comparative or additional material. Some of the more
noteworthy contributions to knowledge of the cottonmouth are the general
accounts of the life history by Allen and Swindell (1948), Barbour
(1956), and Wright and Wright (1957); the publications by Gloyd and
Conant (1943) concerning taxonomy; Klimstra (1959) concerning food
habits; and Allen (1937), Parrish and Pollard (1959), Swanson (1946),
and Wolff and Githens (1939b) concerning the venom. Numerous other
publications, although brief, contain worthwhile contributions. Also of
special interest as a source of material for comparison of cottonmouths
with other crotalids are the works of Fitch (1960) on the copperhead and
of Klauber (1956) on the rattlesnakes.
The cottonmouth has been well known for nearly 200 years. Wright and
Wright (1957) listed the following vernacular names that are applied to
the cottonmouth: black moccasin, black snake, blunt-tail moccasin,
congo, copperhead, cottonmouth water moccasin, cotton-mouthed snake,
gapper, highland moccasin, lowland moccasin, mangrove rattler, moccasin,
North American cottonmouth snake, North American water moccasin, North
American water viper, pilot, rusty moccasin, salt-water rattler,
stubtail, stump (-tail) moccasin, stump-tail viper, swamp lion, Texas
Moccasin, trapjaw, Troost's moccasin, true horn snake, true water
moccasin, viper, water mokeson, water pilot, water rattlesnake, and
water viper.
Some of the names listed above are based upon superstition and folklore
prevailing in pioneer times, and others are based upon the behavior or
appearance of the snake at various ages. Names like "stump-tail
moccasin" are derived from the appearance of females which have short
tails or snakes that have lost part of the tail. Names like "gapper" and
"trapjaw" came to be applied because of the habit of the snake's lying
with its mouth open when approached. The name "cottonmouth" also was
derived from this behavior, although the lining of the mouth is whitish
in most other snakes. The term "rattlesnake" may have come from the fact
that the cottonmouth vibrates its tail vigorously when nervous as do
many other snakes, or it may have been confused with rattlesnakes.
Because of the general public's fear of snakes and their reluctance to
learn to discriminate between the poisonous and harmless species,
numerous kinds of snakes seen in or near water have been called
moccasins. The general appearance, pugnacious behavior, and whitish
mouth of water-snakes (_Natrix_) have earned them a bad reputation. In
fact, a great majority of the "cottonmouths" reported in many areas are
found to be water-snakes.
The cottonmouth is economically important mainly because of the
injurious or fatal effects of its bite and the psychological effect that
its actual or suspected presence has upon many persons. The species eats
a wide variety of prey items and helps to prevent overabundance of
certain kinds of organisms. The venom has been used in the therapeutic
treatment of blood clots owing to its anticoagulant properties
(Didisheim and Lewis, 1956). It also is employed in the treatment of
haemorrhagic conditions and rheumatoid arthritis, as well as in the
production of antivenin (Allen and Swindell, _op cit._:13). None of
these uses of venom has become widely accepted, and its value is
questionable.
ACKNOWLEDGMENTS
For guidance in the course of my study, I am especially indebted to
Professor Henry S. Fitch. For suggestions concerning the preparation of
the manuscript, I thank Professor E. Raymond Hall. I am grateful to my
wife, Janis, for her invaluable assistance and for typing the
manuscript.
For use of specimens in their care, I thank Professors William E.
Duellman, University of Kansas; Robert L. Packard, formerly of Stephen
F. Austin State College; W. Frank Blair, University of Texas; and
William B. Davis and Richard J. Baldauf, Texas Agricultural and
Mechanical College. Mr. John E. Werler of the Hermann Park Zoo, Houston,
Texas, contributed live individuals; Mr. Richard S. Funk contributed
information on the birth of a brood of cottonmouths; and Dr. Henry M.
Parrish contributed information on the incidence of snakebite. To
numerous other persons at leading museums throughout the United States
for information on the cottonmouths in their collections, to all who
helped with the field work in various ways, and to others at the
University of Kansas for their help and suggestions I am grateful.
SYSTEMATIC RELATIONSHIPS AND DISTRIBUTION
Snakes of the genus _Agkistrodon_ are relatively primitive members of
the Crotalidae, which is one of the most specialized families of snakes.
A majority of the pit-vipers are found in the Americas, but close
relatives are found from extreme southeastern Europe through temperate
Asia to Japan (_A. halys_) and southeastern Asia including Indonesia
(_Agkistrodon_ and _Trimeresurus_). Familial characters include:
vertical pupil of the eye; facial pit present between the preoculars and
loreal; scales usually keeled; short, rotatable maxilla bearing a large
hollow fang; toothless premaxilla; chiefly hematoxic venom; and
undivided anal plate.
The genus _Agkistrodon_ includes about nine species in the Old World and
three in North and Central America. Some of the primitive characters of
the genus are: head covered with nine enlarged shields or having the
internasals and prefrontals broken up into small scales; subcaudals on
proximal part of tail undivided; fangs relatively short; tail lacking
rattles. In one species, _A. rhodostoma_, the scales are smooth; and the
female is oviparous and guards her eggs until they hatch. Other species
have keeled scales and are ovo-viviparous.
There is little paleontological evidence illustrating evolution of the
cottonmouth or for that matter of crotalids in general. Brattstrom
(1954) summarized the current knowledge of fossil pit-vipers in North
America. The few fossils found of the cottonmouth are from Alacha,
Brevard, Citrus, Levy, Pasco, and Pinellas counties, Florida
(Brattstrom, _op. cit._:35; Auffenberg, 1963:202). All are of late
Pleistocene Age and well within the present geographic range of the
cottonmouth.
Of crotalid genera only _Agkistrodon_ occurs in both the Old World and
the New World, suggesting that this genus is relatively old. Schmidt
(1946: 149-150) mentioned several other closely related groups of
animals found in both eastern Asia and eastern North America, including
the reptilian genera: _Natrix_, _Opheodrys_, _Elaphe_, _Ophisaurus_,
_Leiolopisma_ (= _Lygosoma_), _Eumeces_, _Clemmys_, _Emmys_, and
_Alligator_. Of the groups of animals now confined to these two regions
the most important are the cryptobranchid salamanders, the genus
_Alligator_, and the spoon-bills (_Psephurus_ in China and _Polyodon_ in
the Mississippi drainage). Fossil evidence for these groups indicates
that existing forms common to eastern Asia and eastern North America are
remnants of a late Cretaceous or early Tertiary Holarctic fauna which
was forced southward as the climate became gradually cooler to the
north. "Other clues suggest that both _Agkistrodon_ and _Trimeresurus_
(_Bothrops_) moved from Asia to America, one of these presumably giving
rise to the rattlesnakes." (Darlington, 1957:228).
The named, American kinds of _Agkistrodon_ currently are arranged as
three species: the copperhead, the cantil and the cottonmouth. The
copperhead (_A. contortrix_) is divided into four subspecies, all of
which are terrestrial. This species occurs from southern New England to
eastern Kansas and along the Atlantic and Gulf Coastal plains, exclusive
of peninsular Florida and the delta of the Mississippi River in
Louisiana. It extends southwest from Kansas through the Edwards Plateau
of west-central Texas. Isolated populations occur in the Chisos and
Davis mountains of Trans-Pecos Texas. The cantil or Mexican moccasin
(_A. bilineatus_), probably the nearest relative of the cottonmouth (_A.
piscivorus_), is divisible into two subspecies and occupies a nearly
complementary range from Mexico south to Nicaragua. The cottonmouth
occurs throughout the coastal plains of the southeastern United States,
usually at altitudes of 500 feet or less. Two subspecies are recognized,
the eastern _A. p. piscivorus_ and the western _A. p. leucostoma_. A
revision of the genus is underway by Professor Howard K. Gloyd.
The basic pattern and various behavioral traits are common to all three
species. The young are more nearly alike in appearance than adults, the
copperhead and the cottonmouth being easily confused. Adults differ in
color, size, body proportions, habitat, and habits. In range and habitat
preference the cottonmouth more closely resembles the southern
subspecies of the copperhead, _A. c. contortrix_, which is usually found
in lowlands, near swamps and streams, but seldom in water.
[Illustration: FIG. 1.]
FIG. 1. Geographic range of the cottonmouth, showing marginal and
near-marginal records, based largely upon maps by Gloyd and Conant
(1943:165) and Conant (1958:336) but including additional records. The
more important of these records (from east to west) are discussed in the
following paragraphs. Crosshatching indicates the area of intergradation
between the eastern and western subspecies. Old records, indicated by
dates, and their sources are as follows: 1850's and 1891--U. S. National
Museum numbers 4263 and 32753 respectively; 1897--Hurter (1897); and
1895--Stejneger (1895:408).
The northernmost record for the eastern subspecies is in the Petersburg
area, Prince George County, Virginia (Anon., 1953:24). A sight record
(Hickman, 1922:39) near Bristol, West Virginia, probably was based on a
water-snake (_Natrix_ sp.), since the stream in which the snake was seen
flows north into the Ohio River rather than southeast through Virginia.
In North Carolina the most inland record is from the Neuse River, six to
eight miles east of Raleigh (Stejneger, 1895:408). Neill (1947:205)
reported a population in the vicinity of Dry Fork Creek on the boundary
line of Wilkes and Oglethorpe counties, Georgia. Distribution of
cottonmouths in Florida is statewide, including the Keys and other
offshore islands.
The ranges of the two subspecies, _piscivorus_ and _leucostoma_, meet
near the eastern border of Mississippi. _A. p. piscivorus_ has been
reported from Tishomingo County to the Gulf and east of the Loess Bluff
area in central Mississippi, and _A. p. leucostoma_ has been reported
from this area westward. A few specimens from along the Coast indicate
intergradation (Cook, 1962:33) between the two subspecies.
Barbour (1956:33) reported one specimen from Cypress Creek, in the Green
River drainage, Muhlenberg County, Kentucky, and stated that suitable
habitat can be found in several areas east of Kentucky Lake. Hence,
cottonmouths may have entered this area via the Ohio River. Stejneger
(_loc. cit._) reported the species in the Wabash River at Mount Carmel,
Wabash County, Illinois, and mentioned a former occurrence at Vincennes,
Knox County, Indiana; but there are no recent records at these
localities. Hurter (1897) reported having seen cottonmouths in Illinois,
opposite St. Louis; Smith (1961:265) believes that this and a population
in Monroe County, Illinois, are isolated relicts, since no specimens
have been found within 50 miles to the south of Monroe County. The
specimens reported by Anderson (1941:178; 1945:274) near Chillicothe
(three miles southwest and seven miles northwest, respectively),
Livingston County, Missouri, also are thought to represent a relict
population. Hall and Smith (1947:453) reported one specimen from Jasper
County, Missouri, in the Spring River which flows through extreme
southeastern Kansas and into Oklahoma and another in the Neosho River at
Chetopa, Kansas. Both of these specimens were taken after a flood, and
no additional specimens have been taken in this region. Nevertheless,
sufficient habitat is probably available along the Neosho and Verdigris
rivers in the southeastern part of Kansas.
In Texas the cottonmouth has penetrated marginal habitat perhaps farther
than anywhere else in its range. Formerly it was thought to be limited
to the country east of the Balcones Escarpment (Smith and Buechner,
1947:8), but semiarid areas of the state have been invaded primarily via
the Colorado and Brazos River systems up to altitudes of 2300 feet. Two
additional specimens are said to have been collected along the Rio
Grande. Dr. Howard K. Gloyd (_in litt._) stated that the specimen
reported from Eagle Pass, Maverick County, is believed to have been
taken in the 1850's; and the one said to have come from the mouth of the
Devil's River is actually marked "near Santa Rosa, Cameron County,
September 30, 1891." No additional specimens have been taken in that
area; and the range now probably extends no farther south than Corpus
Christi, Texas. Brown's (1903:554) knowledge of the extension of the
range of the cottonmouth west of longitude 98° is probably based upon
the records along the Rio Grande reported in the nineteenth century.
Three extensions of the known range in Texas are reported herein. One
specimen was captured by Mr. Harry Green (HWG 346) along the San Saba
River, 8.1 miles west of Menard, Menard County. The other two specimens
(KU 84375 and 84376) were taken by the late Paul Anderson one and
one-half miles north of Pecan Crossing, South Concho River, Tom Green
County, and one mile west of Mertzon, Irion County.
In the hypsithermal period following Pleistocene glaciation,
cottonmouths gradually moved northward occupying areas beyond their
present range. The distributional records since the 1850's and the
apparent relict populations now in existence indicate that the range
of this species has since receded.
DESCRIPTION
Color and Pattern
Color predominantly brown, ranging through pale reddish-brown or dark
reddish-brown, brownish-green, to almost black; 10 to 17 irregular dark
brown bands on paler brown ground color; young paler (some nearly salmon
pink), retaining a vivid pattern throughout first year; pattern of most
individuals nearly obliterated by third year; brilliance and dullness of
predominant color correlated with molting cycle (skin especially bright
and shiny immediately following shedding); tip of tail yellowish in
juveniles; posterior part of venter and tail uniformly black in some
adult individuals, especially females; secondary sexual differences in
dorsal coloration, such as found in copperhead by Fitch (1960:102), not
noted.
The eastern subspecies, _A. p. piscivorus_, has the more brilliant
pattern in which the centers of the dark cross-bands are invaded by the
ground color. The cross-bands are slightly constricted in the mid-line
and may or may not be bilaterally symmetrical. One-half of the
cross-band may be displaced anteriorly or posteriorly to a slight degree
or may even be completely absent. From one to several dark spots may be
present within the cross-bands.
The western subspecies, _A. p. leucostoma_, has a comparatively dull
pattern in which the ground color does not invade the center of the
cross-bands. In many instances the bands are outlined by white scales,
as in the Mexican moccasin (this character is not so prominent in _A. p.
piscivorus_ because of the paler ground color). A large, dark blotch
usually occurs at the base of the cross-band and may completely cross
the ventral scales. The characteristic variations found in _piscivorus_
are also present in _leucostoma_.
The number of bands is often difficult to count because of the dark
color of some specimens. Gloyd and Conant (1943:168) reported averages
of 12.5 (11 to 16) and 12.2 (10 to 16) in males and females,
respectively, of _leucostoma_ and ranges of 10 to 17 for males and 10 to
16 for females with averages of 13 in both sexes of _piscivorus_. On 20
specimens of _leucostoma_ from Texas the average number of bands was
12.7 (11 to 15). If the number of bands differed on the two sides of an
animal, the total number of the two sides was divided by two.
Scutellation
The scutellation of the cottonmouth closely resembles that of the other
species of _Agkistrodon_. For example, the nine cephalic shields are
characteristic of most species of _Agkistrodon_, as well as most other
primitive crotalids and viperids, and most colubrids. Most individuals
have an additional pair of large scales behind the parietals.
The numbers of postoculars, supralabials, and infralabials are variable.
On either side the postoculars (three in most specimens) are reduced to
two in some specimens. The supralabials (eight in most specimens)
frequently vary (usually on one side only) from seven to nine. The
number of infralabials is somewhat more variable than the number of
supralabials, the usual number being 11, but 10 is also common; 8, 9,
and 12 are more rare (Table 1). In 102 snakes in which these characters
were examined, four different combinations of supralabials and seven
combinations of infralabials were found. Both characters together
yielded 16 combinations, considering only the actual number of scales
and not taking into account the side of the head on which they occurred
(Table 2). The combinations found in a brood of seven young from
Houston, Texas, are shown in Table 3 to illustrate the variability of
this character. Gloyd and Conant (1943:168) found a variation of 6 to 11
(8) and 7 to 9 (8) supralabials and 8 to 13 (11) and 8 to 12 (10.4)
infralabials in samples of 301 _leucostoma_ and 119 _piscivorus_,
respectively (numbers in parentheses represent average). Also of
interest is the variability of the scales themselves. In one instance a
scale was found that had not completely divided. In another specimen the
last supralabial and last infralabial were one scale that completely
lined the angle of the jaw. Instances of one scale almost crowding out
another were common. In still other instances one or two supralabials
were divided horizontally into two scales. Individual variation rather
than geographical variation occurs in these characters.
TABLE 1.--Frequency of Occurrence of Various Numbers of
Supralabial and Infralabial Scales in 102 Cottonmouths.
====================================================
| |Specimens |Specimens | | |
|Number |having |having |Total |Percentage |
|of scales |number on |number on | | |
| |both sides |one side | | |
|----------------------------------------------------|
| Supralabials |
|----------------------------------------------------|
| 7 | 11 | 24 | 35 | 25.2 |
| 8 | 64 | 27 | 91 | 65.5 |
| 9 | 0 | 3 | 3 | 2.2 |
|----------------------------------------------------|
| Infralabials |
|----------------------------------------------------|
| 8 | 0 | 2 | 2 | 1.5 |
| 9 | 3 | 10 | 13 | 9.6 |
| 10 | 12 | 32 | 44 | 32.4 |
| 11 | 53 | 22 | 75 | 55.1 |
| 12 | 0 | 2 | 2 | 1.5 |
----------------------------------------------------
TABLE 2.--Numbers of Supralabials and Infralabials of 102
Cottonmouths.
===========================================
| Number of | Number of | Number of |
| individuals | supralabials | infralabials |
| 37 | 8 | 11 |
| 15 | 8 | 10-11 |
| 12 | 7-8 | 11 |
| 6 | 7-8 | 10-11 |
| 5 | 8 | 10 |
| 5 | 8 | 9-10 |
| 4 | 7 | 11 |
| 3 | 7 | 9-10 |
| 3 | 7-8 | 10 |
| 2 | 7 | 9 |
| 2 | 7 | 10 |
| 2 | 8 | 10-12 |
| 2 | 8-9 | 10 |
| 2 | 7-8 | 8-9 |
| 1 | 7-8 | 9 |
| 1 | 8-9 | 10-11 |
-------------------------------------------
The dorsal scales of cottonmouths are strongly keeled except that those
of the two lower scale-rows on each side are weakly keeled. Also they
are slightly larger than the others. Two apical pits are present on each
dorsal scale. The shape of the scales and number of scale rows vary
depending upon the position on the body. Scales on the neck are
considerably smaller than those elsewhere on the body and are arranged
in two or three more rows than those at mid-body. The skin in the region
of the throat, neck, and fore-body is especially elastic and allows the
swallowing of large prey. Posteriorly from the mid-body the scales
decrease in size and become more angular, those on the tail tending to
be rhomboidal and wider than long. In the region of the anus the number
of scale rows diminishes rapidly, leaving only 12 to 14 rows at the base
of the tail and only three rows immediately ahead of the tail tip. The
tail ends in a spine composed of two scales: one scale covers the
bottom, lower parts of the sides, and tip of the spine; and a shorter
dorsal scale covers the top and upper parts of the sides of the basal
two-thirds of the spine. The spine of embryos and young cottonmouths is
blunt, but is pointed in most adults.
TABLE 3.--Variation in Numbers of Supralabials and Infralabials
in a Brood of Seven Cottonmouths.
===========================================
| Number of | Number of | Number of |
| individuals | supralabials | infralabials |
| 1 | 7 | 9 |
| 1 | 7 | 9-10 |
| 2 | 7-8 | 8-9 |
| 1 | 7-8 | 9 |
| 1 | 8 | 9-10 |
| 1 | 8-9 | 10 |
-------------------------------------------
TABLE 4.--Analysis of Number of Scale Rows at Three Parts of
the Body in 81 Cottonmouths.
==============================================================
| | Neck | Mid-body | Anterior to anus|
| |--------+--------+--------+--------+--------+--------|
| Number | Number | Per- | Number | Per- | Number | Per- |
| of | of |centage | of |centage | of |centage |
| scales |indivi- | |indivi- | |indivi- | |
|per row | duals | | duals | | duals | |
|--------+--------+--------+--------+--------+--------+--------|
| 29 | 1 | 1.2 | ... | ... | ... | ... |
| 28 | 3 | 3.7 | ... | ... | ... | ... |
| 27 | 52 | 64.2 | ... | ... | ... | ... |
| 26 | 16 | 18.0 | 2 | 2.5 | ... | ... |
| 25 | 8 | 9.9 | 67 | 82.7 | ... | ... |
| 24 | 1 | 1.2 | 4 | 4.9 | ... | ... |
| 23 | ... | ... | 8 | 9.9 | 4 | 4.9 |
| 22 | ... | ... | ... | ... | 4 | 4.9 |
| 21 | ... | ... | ... | ... | 68 | 84.0 |
| 20 | ... | ... | ... | ... | 5 | 6.2 |
--------------------------------------------------------------
The number of scale rows on the neck, at mid-body, and just anterior to
the anus is relatively constant at 27-25-21, respectively; but some
individual variation is evident (Table 4). Since the rows are diagonally
arranged, it is necessary in counting scales to proceed either
anteriorly or posteriorly across the back; or the row may be counted in
either direction up to the center of the back and then reversed on the
other side of the snake. In order to count the scale rows in a position
where no scale reduction or addition was occurring and to avoid as much
error as possible, I counted from anterior to center and back on the
neck, in any direction at mid-body, and from posterior to center and
back near the anus. Because females generally are the larger in
circumference posteriorly, they could have more scale rows than males
just anterior to the anus. The few snakes having more than 21 scale rows
in the posterior region offer no conclusive evidence as to tendencies,
but in both instances in which this occurred the females outnumbered the
males three to one. An odd, rather than an even, number of scale rows
occurs on most of the length of the snakes examined, because there is a
mid-dorsal row and scale rows tend to be lost on both sides at about the
same level. An example of scale reduction of one snake was as follows:
6+7 (13) 6+7 (96)
27 -------- 25 -------- 24 -------- 23 --------- 22 ---------
5+6 (13) 5+6 (90) 7+8 (111) 7+8 (114)
6+7 (122) +7, -5 (125)
23 -------- 22 -------- 23 --------- 21 -------- 22 ------------
-6 (118) +6 (119) 6+7 (121) +6 (123)
-6 (126)
22 -------- 21 (130).
This scale reduction follows the method proposed by Dowling (1951b: 133)
in which the numbers on the mid-line represent the number of scale rows,
upper figures refer to the right side of the snake, and figures in
parentheses indicate the number of the ventral scale (counted from the
anterior end of the series), thus marking the position of the addition
or reduction. Addition of a row is shown by a plus sign and the number
of the row, whereas reductions are shown by a minus sign and the number
of the row that is lost or by a plus sign between the number of two rows
that join. According to Dowling, variation in number of dorsal scales
characterizes the few genera and species of snakes in which it has been
studied. The time and difficulty involved in ascertaining the number of
scales explain why it has not been widely used in classification.
[Illustration: FIG. 2. Number of ventral scales in 48 female and 34
male _A. p. leucostoma_.]
Ventral scales on 34 males averaged 134.4 (128 to 139), and on 48
females 133.5 (128 to 137) (Fig. 2.). Barbour (1956:34) found an average
of 135.3 ventral scales on 64 males and 44 females, and Gloyd and Conant
(_loc. cit._) found an average of 134 for both males and females. The
average for the eastern cottonmouth obtained by Gloyd and Conant,
however, was 137 ventrals in both sexes. Some of my counts were made
before I knew of the standard system of counting ventrals proposed by
Dowling (1951a:97-99), in which the first ventral plate is defined as
the most anterior one bordered on both sides by the first row of
dorsals. Therefore, some inconsistencies may exist in my counts. Where
differences occur, Dowling's method probably will indicate the presence
of an additional scale, since it appears to begin farther anteriorly on
the average, than I began counting.
[Illustration: FIG. 3. Number of caudal scales in 44 female and 34
male _A. p. leucostoma_.]
TABLE 5.--Caudal Scale Combinations in 95 Cottonmouths.
U = Undivided; D = Divided.
=====================================================================
| Number of scales
|-------------------------------------------------------------
Number | | | | | | | | | | | | | | | | |
of | | | | | | | | | | | | | | | | |
samples| D | U | D | U | D | U | D | U | D |U| D|U| D|U|D|U|D
-------+---+-----+-----+---+----+---+----+---+-----+-+--+-+--+-+-+-+-
25 | |13-35|10-32| | | | | | | | | | | | | |
11 |1-2|12-33|14-28| | | | | | | | | | | | | |
20 | |16-39| 1-9 |1-3|3-24| | | | | | | | | | | |
20 |1-4| 3-37| 1-21|1-5|1-29| | | | | | | | | | | |
4 | |14-30| 1-8 |1-7|1-8 |1-4|2-10| | | | | | | | | |
3 | 1 |18-23| 1-2 |1-2|6-11|1-3|6-9 | | | | | | | | | |
4 | | 1-17| 1 |1-3|1-8 |1-4|1-3 |1-4|13-22| | | | | | | |
2 |1-2| 4-16| 1 |1-4| 2 | 1 |1-4 | 1 |18-21| | | | | | | |
1 | | 20 | 1 | 1 | 1 | 1 | 6 | 1 | 3 |1|11| | | | | |
1 | | 10 | 2 | 3 | 2 |10 | 1 | 2 | 2 |1| 4|4| | | | |
1 | | 20 | 1 | 1 | 2 | 1 | 1 | 4 | 4 |2| 4|1| 3| | | |
1 | 1 | 13 | 1 | 1 | 1 | 3 | 1 | 1 | 1 |4| 2|4|13| | | |
1 | | 17 | 1 | 1 | 2 | 1 | 1 | 6 | 2 |1| 2|3| 2|7| | |
1 | | 9 | 1 | 1 | 8 | 1 | 3 | 1 | 1 |3| 1|1| 2|1|1|1|6
---------------------------------------------------------------------
Analysis of caudal scales revealed sexual dimorphism. In the six
specimens from Tennessee, Blanchard (1922:16) found the same thing.
Caudals averaged 45.4 (41 to 50) on 34 males and 42.6 (39 to 49) on 44
females (Fig. 3). Barbour (_loc. cit._) found an average of 45.7 (30 to
54) caudals in males and 43 (17 to 56) in females. Caudal scale counts
by Gloyd and Conant (_loc. cit._) averaged 44 (38 to 49) in males and 42
(37 to 48) in females of _leucostoma_; in _piscivorus_ they averaged 48
(42 to 53) in males and 44 (41 to 49) in females. Another
seldom-mentioned, unusual characteristic of the caudal scales of
copperheads and cottonmouths is that some are single (usually those at
the base of the tail) and others divided (Table 5). To my knowledge, all
other species have either single or divided scales the entire length of
the tail. See Klauber (1941:73) and Fox (1948:252) concerning
correlation of few scales with warm environment.
Dentition
Cottonmouths, like other pit-vipers, have their teeth reduced in number
and have enlarged, highly specialized fangs. Small teeth occur on the
palatine and the pterygoid in the upper jaw and on the dentary in the
lower jaw. The dentary bone bears 17 curved teeth that decrease in size
posteriorly. The palatine bears five small, strongly curved teeth, and
the pterygoid bears 16 to 18 strongly curved teeth decreasing in size
posteriorly. The numbers of teeth mentioned above in each instance refer
to the number of sockets rather than the actual number of teeth, because
teeth are frequently shed, leaving some of the sockets empty at any one
time.
The maxillary bone has two sockets side by side which bear the poison
fangs, usually one at a time. During the period shortly before a fang is
to be shed, however, its replacement becomes attached in the alternate
socket; and both fangs may be functional for a short time. The old fang
then becomes weakened at its base, eventually breaks off, and is
swallowed. At any one time four or five replacement fangs in various
stages of development are found in the gum behind the functional fang.
These replacement fangs, which are arranged in alternate rows, gradually
enlarge as they move forward in their development and, in juveniles, are
generally slightly longer than the fangs that they replace.
In 1963 I examined the fangs of 14 cottonmouths at four- to seven-day
intervals for a period of six weeks. The fang-shedding cycle was found
to be highly irregular, with a double condition (on one or both sides)
occurring one-third of the time. Approximately the same proportion of
double fangs was found in preserved individuals. A replacement period of
at least five days was observed in one snake. One-half the cycle (from
replacement on one side to replacement on the other) varied from five to
twenty days, indicating that the cycles for each fang are independent of
one another. Bogert (1943:324) found that young rattlesnakes are born
with functional fangs in the two inner sockets. Nonsynchronous use of
the sockets on opposite sides of the head in rattlesnakes is a later
development which results from accidents or other conditions leading to
a longer retention of the fang on one side than on the other (Klauber,
1956:723). I found a double set of fangs in cottonmouths only twice in
the six-week period. A complete cycle was recorded in ten instances in a
period of 19 to 23 days and in two instances in 32 days. One cottonmouth
was examined periodically over a 34-day period by Allen and Swindell
(1948:12), but a complete fang-shedding cycle was not observed. Fitch
(1960:110) reported a 33-day cycle in copperheads; Klauber (1956:726)
estimated the normal active life of each fang of an adult rattlesnake to
be from six to ten weeks, but he made no observations to confirm his
estimation.
Fangs measured from the tip of the notch of the basal lumen to the end
of the fang vary from about 1.3 per cent of the snout-vent length in
juveniles to about 1.0 per cent in large adults (Table 6). The fangs are
longer than those of copperheads (Fitch, 1960:111). Klauber's (1956:736)
figures on fang-lengths in all species of rattlesnakes are percentages
of total length rather than of the snout-vent length. The fangs of
various species of rattlesnakes range from nearly the same proportionate
length as those of cottonmouths to some much longer.
From patterns of bites of venomous snakes, Pope and Perkins
(1944:333-335) attempted to correlate number, size, and patterns of
tooth marks with size and generic identity of the snake responsible for
the bite. Distance between fangs is relatively constant for snakes of a
particular size (Table 6) regardless of genus, but the fangs of a
cottonmouth are directed outward to variable degrees, and puncture
wounds could easily resemble those of a much larger snake (Table 7).
Also there is no direct relationship between size of snake and toxicity
or amount of venom injected. Consequently information of this kind is of
little or no value from a medical standpoint.
TABLE 6.--Correlation of Relative Fang-length and Distance
Between Fangs at Base with Snout-vent Length of Cottonmouths.
=======================================================
|Snout-vent |Number |Average |Number |Average |
|length |in |ratio of |in |ratio of |
|(millimeters) |sample |fang-length |sample |distance |
| | |to | |between |
| | |snout-vent | |fangs to |
| | |length | |snout-vent |
| | |(percent) | |length |
| | | | |(percent) |
|--------------+-------+------------+-------+-----------|
| 200-299 | 3 | 1.33 | 3 | 2.57 |
| 300-399 | 7 | 1.30 | 5 | 2.48 |
| 400-499 | 13 | 1.21 | 9 | 2.21 |
| 500-599 | 12 | 1.22 | 8 | 2.19 |
| 600-699 | 7 | 1.17 | 1 | 2.10 |
| 700-799 | 5 | 1.07 | 4 | 1.65 |
| 800-899 | 1 | 1.00 | 1 | 2.00 |
-------------------------------------------------------
TABLE 7.--Contrast in Measurements Between the Base of the
Fangs and Between Fang Punctures of Nine Cottonmouths (in
millimeters).
==================================================
| Distance between | Distance between | Snout-vent |
| base of fangs | fang punctures | length |
|------------------+------------------+------------|
| 7.7 | 13.0 | 400 |
| 8.7 | 14.0 | 575 |
| 10.0 | 22.5 | 526 |
| 11.0 | 18.0-19.0 | 590 |
| 12.0 | 18.0 | 793 |
| 13.0 | 17.0, 20.0 | 558, 612 |
| 15.5 | 23.5 | 800 |
| 16.0 | 24.0 | 800 |
--------------------------------------------------
HABITAT AND LIMITING FACTORS
Although usually associated with swamps and lowlands along river
bottoms, the cottonmouth lives in a variety of habitats ranging from
salt marshes to cool, clear streams and from sea level to an altitude of
2300 feet. Shaded, moist areas either in or beside shallow waters are
preferred, but cottonmouths occasionally wander as far as a mile from
water.
In the pine-oak forests of Nacogdoches County in eastern Texas
cottonmouths and copperheads are probably the most abundant species of
snakes. Specimens have been collected near Nacogdoches in ponds, swamps,
clear and fast-running streams with rock bottoms, and sluggish muddy
streams. On the Stephen F. Austin Experimental Forest numerous
cottonmouths live in a swamp until around mid-July, when it becomes dry.
A small stream west of the swamp seems to be used as a migration route
to and from the swamp. Slightly more than a mile downstream cottonmouths
are common in a bottomland area. The ground is always moist and no
undergrowth occurs; a few small clear springs produce shallow trickles
that run into a swamp. Cottonmouths can often be found here, lying in or
beside the small trickles.
I have seen cottonmouths in various types of aquatic habitats in
Brazoria County. In most places in this area, cottonmouths are found in
association with one or more species of water-snakes (including _Natrix
cyclopion_, _N. erythrogaster_, _N. rhombifera_, and _N. confluens_),
which greatly outnumber the cottonmouth. Interspecific competition may
be reduced somewhat by cottonmouths sometimes feeding on water-snakes.
The numerous statements in the literature concerning the habitat of the
cottonmouth can be summarized most easily by the following short
quotations:
_Agkistrodon piscivorus piscivorus_--"Marshes and lakes; ponds
and streams with wooded shores; low country near water;
roadside ponds; drainage ditches; coastal 'banks'; keys; some
Gulf coast islands; mangrove swamps." (Wright and Wright,
1957:919.)
_Agkistrodon piscivorus leucostoma_--"Cypress, gum, river
swamps; alluvial swamps wooded or not wooded; water courses of
the south such as rivers, bayous, backwaters of small branches;
hill streams in the north; ... marshy places in prairies ...
rice fields, bottomland pools; margins of above habitats,
pools, shallow lakes, swampy places, temporary flood lands....
In, under, or on fallen timber, in holes in banks, rocky
bluffs, crayfish burrows. In short it is very aquatic." (Wright
and Wright, _op. cit._:923.)
Geographically cottonmouths differ somewhat in their ecological
requirements, but are basically much alike in most respects. The areas
of greatest abundance are those having 40 inches or more of annual
rainfall. The northern edge of the range has a mean temperature of
approximately 38° F. in January in Virginia and 30° F. in Missouri,
although the lowest temperature reached in these areas is more important
as a limiting factor. The annual rainfall in both Virginia and Missouri
amounts to approximately 40 inches. Moisture, as well as temperature,
may play an important role in the northward distribution of the species.
The eastern cottonmouth seems to be less tolerant of low temperatures
than the western subspecies. Mean January temperatures equal to those
along the northern limits of the western cottonmouth's distribution are
reached in the vicinity of Connecticut, which is north of the geographic
range of the eastern subspecies.
The depths to which cottonmouths penetrate into their dens may have a
limiting influence upon the geographic range, especially in the northern
extremes. Bailey (1948:215) discussed the possibility that populations
of snakes may be significantly depressed because of winter kill of
individuals that "hibernate" at shallow depths. He speculated also that
the short growing season does not allow enough time for the essentials
of existence to be carried out, and the prolonged period of inactivity
overtaxes the energy reserve of the species.
Available food does not seem to be of much importance as a limiting
factor, for the cottonmouth is remarkably indiscriminate in its choice
of prey, feeding upon almost any vertebrate animal that happens to come
within reach. Competition for food, however, may play an important role.
REPRODUCTION
Courtship and Mating
A review of available literature indicates no records of courtship of
the cottonmouth other than statements that breeding occurs in early
spring. In a close relative, the copperhead (see Fitch, 1960:159-160),
mating occurs almost any time in the season of activity but is mainly
concentrated in the few weeks after spring emergence, at about the time
when females are ovulating. Klauber (1956:692) concluded that along the
southern border of the United States rattlesnakes normally mate in
spring soon after coming out of their winter retreats; but farther north
where broods are produced biennially, the mating times may be more
widely dispersed, and summer and fall matings may even predominate.
The only record of copulation in the cottonmouth was reported by Allen
and Swindell (1948:11), who observed a pair copulating for three hours
on October 19, 1946, at the Ross Allen Reptile Institute. Davis
(1936:267-268) stated that courtship in cottonmouths is violent and
prolonged but did not note any nervous, jerky motions or nudging of the
female along her back and sides as had been observed in other genera of
snakes. Carr (1936:90) saw a male cottonmouth seize a female in his
mouth and hold her, but no courtship followed.
Reproductive Cycles
Many persons have assumed that gestation periods in snakes are the
intervals between mating and parturition, and that mating and ovulation
occur at approximately the same time. However, retention of spermatozoa
and delayed fertilization indicate that copulation is not a stimulus for
ovulation.
A biennial reproductive cycle was found for the copperhead in Kansas
(Fitch, 1960:162), the prairie rattler in Wyoming (Rahn, 1942:239) and
in South Dakota (Klauber, 1956:688), the great basin rattler in Utah
(Glissmeyer, 1951:24), and the western diamondback rattler in
northwestern Texas (Tinkle, 1962:309). Klauber's (1956:687) belief that
the reproductive cycle of rattlesnakes varies with climate, being
biennial in the north and annual in the south, is supported by similar
climatic variation in the reproductive cycle of the European viper which
was discussed by Volsøe (1944:18, 149).
If data for a large number of females were arranged as are those in
Table 8, they might reveal whether the breeding cycle is annual or
biennial. The figures presented in Table 8 are misleading if viewed
separately because of the small number of individuals included in some
of the size classes.
The smallest reproductive female found measured 455 millimeters in
snout-vent length. Conant (1933:43) reported that a female raised in
captivity gave birth to two young at an age of two years and ten months.
The size classes represented by gravid females found by Barbour
(1956:38) in Kentucky indicate that breeding occurs at least by the
third year.
The ovaries of female cottonmouths examined revealed ova in various
stages of development. In individuals less than 300 millimeters in
snout-vent length the ovaries are almost completely undeveloped; in
immature individuals from 300 to 450 millimeters in length the follicles
are from one to two millimeters in length; in post-post females
follicles vary in size, the largest being about seven millimeters.
Reproductive females also contain follicles of various sizes. One or two
sets are less than three millimeters in length, and large ova that soon
are to be ovulated are present. Ovarian ova found in April ranged in
length from 23 to 35 millimeters. No embryonic development was observed
in most individuals until June or later.
TABLE 8.--Percentage of Gravid Females of _A. p. leucostoma_ in
50 Millimeter Size Classes.
=====================================
|Snout-vent |Number |Total |Percentage|
| | of |number| |
| length |gravid | in | gravid |
| |females| size | |
| | |class | |
|-----------+-------+------+----------|
| 450-499 | 3 | 14 | 21.4 |
| 500-549 | 7 | 17 | 41.2 |
| 550-599 | 8 | 17 | 47.1 |
| 600-649 | 5 | 7 | 71.4 |
| 650-699 | 2 | 9 | 22.2 |
| 700-749 | 2 | 3 | 66.7 |
| 750-799 | 1 | 1 | 100.0 |
| 850-899 | 1 | 1 | 100.0 |
| Totals | 29 | 69 | 42.0 |
-------------------------------------
Increase in length of testes appears to be correlated with length of the
individual rather than cyclic reproductive periods (Fig. 4).
The reproductive cycle in cottonmouths resembles that illustrated by
Rahn (_op. cit._:237), in which the ovarian follicles of post-partum
females begin to enlarge in late summer and autumn, with ovulation
occurring the following spring. By means of retaining sperm successive
broods possibly are produced after only one mating. In captivity, at
least, some females may not follow this biennial cycle; Stanley Roth
(M.S.), biology teacher in high school at Lawrence, Kansas, had a female
of _A. p. piscivorus_, from Florida, that produced broods of 14 and 12
young in two consecutive years.
[Illustration: FIG. 4. Length of testes in cottonmouths of various
sizes (·--left; º--right). The right testis is always longer than
the left.]
Embryonic Development
After ova are fertilized a three and one-half to four-month period of
development begins which varies somewhat depending on the temperature.
In almost every instance the ova in the right uterus outnumber those in
the left. Embryos usually assume the serpentine form in the latter part
of June and are coiled in a counterclockwise spiral with the head on the
outside of the coil. At this time the head is relatively large and
birdlike in appearance with conspicuous protruding eyes. Sex is easily
noted because the hemipenes of males are everted. By late July scales
are well developed and the embryo is more snakelike in appearance, but
pigmentation is still absent. By mid-August the color and pattern are
well developed, the egg tooth is present, the snake shows a considerable
increase in size over that of the previous month, and much of the yolk
has been consumed. Some females that contain well developed embryos also
contain eggs that fail to develop. Sizes of ova vary irrespective of
size of female and stage of embryonic development. Lengths of ova ranged
from 22 to 51 millimeters in May to 35 to 49 millimeters in July and
August. A two-yolked egg was found in one female.
Birth of Young
Accounts in the literature of 15 litters of cottonmouths fix the time of
birth as August and September. Conant (1933:43) reported the birth of a
litter in mid-July by a female that had been raised in captivity, and
one female that I had kept in captivity for two months gave birth to a
litter between October 19 and October 25. The conditions of captivity
undoubtedly affected the time of birth in both instances.
Wharton (1960:125-126) reported the birth and behavior of a brood of
seven cottonmouths in Florida. I was given notes of a similar nature by
Richard S. Funk of Junction City, Kansas, on a brood of five
cottonmouths. The mother of the brood was caught in June, 1962, in
Tarrant County, Texas, by Richard E. Smith, and was 705 millimeters in
snout-vent length. The first young was found dead in an extended
position a few inches from the fetal membranes at 11:05 p.m. on August
22. The second young was born at 11:07 p.m. The intervals between the
successive births were three, seven, and four minutes; and time until
the sac was ruptured in each instance was six, five, eight, and 11
minutes. The time interval between the rupture of the sac and emergence
of each individual was 41, 92, 154, and 34 minutes. The mother's actions
in giving birth to the last four young were essentially as described by
Wharton (_loc. cit._), except that the intervals between successive
births did not increase. Within one minute after rupturing the sac and
while its head was protruding, each of the four living young opened its
mouth widely from three to seven times, then took its first breath.
Breaths for the first three hours were steady at three or four per
minute but then decreased to two or three per minute. Pulse rate for the
four averaged 38 per minute while at rest but increased to 44 per minute
after voluntarily crawling.
Number of Young per Litter
Records of from one to 16 young per litter have been reported (Ditmars,
1945:330; Clark, 1949:259), but the average is probably between six or
seven. Most accounts in the literature present information on number of
ova or embryos per female rather than the number of young. Size and age
of the mother (Table 9) influence the number of ova produced. Allen and
Swindell (1948:11) recorded three to 12 embryos in 31 cottonmouths
varying in total length from 26 to 44 inches. An average of 6.5 embryos
per female was found.
TABLE 9.--Number of Ova Produced by Fecund Cottonmouths.
====================+============+======================
Snout-vent length | Number | Number of ova,
in millimeters | in sample | average and extremes
--------------------+------------+----------------------
450-549 | 10 | 4.1 (2 to 7)
550-649 | 11 | 4.9 (1 to 8)
650-749 | 4 | 6.3 (4 to 8)
750-849 | 1 | 5
850-949 | 1 | 14
--------------------------------------------------------
Mortality at birth has been recorded for almost every litter born in
captivity (see Allen and Swindell, _loc. cit._; Conant, 1933:43;
Wharton, 1960:125). A female that I kept in captivity gave birth to
seven young. Three never ruptured their sacs, and another died soon
after leaving the sac. The effects of captivity on females may result in
higher rates of deformity and mortality in young than is common in
nature. Klauber (1956:699-700) estimated that the defects brought about
by conditions of captivity on rattlesnakes eliminate about three young
per litter.
Population Composition
No investigator has yet analyzed the composition of a population of
cottonmouths according to age, sex and snout-vent length. Barbour
(1956:35) did sort 167 snakes into size classes, but did not determine
sex ratio, size at sexual maturity, reproductive cycles, or snout-vent
length. He recorded total lengths from which snout-vent lengths cannot
be computed because of differential growth rates and different bodily
proportions of the two sexes. I judge from my findings that he included
immature individuals in his three smallest size classes (45.5 per cent
of the population). I found at least 32.5 per cent immature individuals
(Fig. 5) in my material, but it was not a natural population.
The sex ratios of several small collections from natural populations
varied, and no conclusions could be drawn. Females comprised 53 per cent
of the specimens included in Fig. 5 and in a group of 48 embryos which
represented eight broods. That percentage may not be the percentage in a
natural population but is used in making assumptions because I lack
better information.
Reproductive Potential
If data in Fig. 5 are representative of a natural population and if 61
per cent of the females are sexually mature, the reproductive potential
can be estimated as follows: assuming a cohort of 1000 cottonmouths
contains 530 females, 61 per cent of the females (323 individuals)
probably are adults. If 42 per cent of these females produce 6.5 young
per female in any season (Tables 8 and 9), 136 females will produce 884
young. But if 50 per cent of the adult females are reproductive (as
would be assumed if reproduction is biennial), 1050 young will be
produced. Actually the number of young required per year to sustain a
population is unknown, because mortality rates at any age are unknown.
[Illustration: FIG. 5. Composition of a group of cottonmouths examined
in this study. Individuals less than 450 millimeters in snout-vent
length are considered as immature. Specimens from 200 to 249 millimeters
in length are included in the 200-millimeter class, _etc._]
GROWTH AND DEVELOPMENT
Size at Birth and Early Growth
Size at birth depends on the health of the mother. According to Fitch
(1960:182), many litters of copperheads born in captivity are stunted.
Seven young cottonmouths (two males and five females) born in captivity
were each 185 millimeters in snout-vent length and 40 millimeters in
tail length. Weights of the three living young were 10.0, 10.1, and 11.1
grams. Another litter of five young measured by Richard S. Funk were
larger, and differences in the proportions of the tail length and
snout-vent length suggest the sexual dimorphism found in larger
individuals. However, sex of these young snakes was not recorded.
Snout-vent length and tail length in millimeters were 232, 41; 243, 47;
229, 40; 240, 48; and 225, 40 in the order of their birth. These snakes
are considerably smaller than the nine young of _A. p. piscivorus_
reported by Wharton (1960:127) that averaged 338 millimeters total
length and 28.7 grams. The yolk of one young _piscivorus_ was 11.7 per
cent of the total weight. Yolk is used up in about two weeks if its rate
of utilization resembles that of the copperhead as reported by Gloyd
(1934:600).
Early rates of growth of three living young are shown in Table 10. On
the 56th day after birth, each was fed one minnow less than two inches
long. Between the 80th and 120th days three additional small minnows
were fed to each snake. Young cottonmouths increase nearly 50
millimeters in length by the first spring if they inhabit warm areas and
feed in autumn or winter.
Variation in size of newborn cottonmouths may be less in nature than in
captivity. Average size at birth can be determined accurately by the
size of young captured in early spring, at least in northern parts of
the range where winter feeding and growth do not occur at all or are
negligible. Total lengths of 19 juveniles thought by Barbour (1956:38)
to be seven to eight months old do not differ markedly from lengths of
the five newly-born young measured by Funk.
TABLE 10.--Rate of Growth of Three Young Cottonmouths.
========+=================================================
| | Snout-vent length/tail length--weight in grams |
| Age +----------------+----------------+----------------|
|in days | Female No. 1 | Female No. 2 | Male |
|--------+----------------+----------------+----------------|
| 2 | 185/40--11.1 | 185/40--10.1 | 185/40--10.0 |
| 7 | 192/40-- | 190/40-- | 189/40-- |
| 22 | 195/40--10.3 | 200/41.5--10.6 | 197/40-- |
| 80 | 204/40--11.7 | 203/42--10.4 | 218/48--14.3 |
| 88 | .... | 204/44-- | .... |
| 143 | 215/40.5--13.3 | .... | 225/48--15.1 |
--------+----------------+----------------+----------------
The Umbilical Scar
The umbilical cord is broken at birth and the navel closes within a few
days; but the scar, involving from two to four ventral scales, remains
throughout life. Position of the scar was found by Edgren (1951:1) to be
sexually dimorphic in the eastern hog-nose snake (_Heterodon
platyrhinos_), but nothing has been published on this matter concerning
the cottonmouth. Consequently, I counted the scales of several
individuals from the anal plate, and there was no marked difference in
the position of the scar in males and females; it varied in position
from the 10th to the 18th scale. When counted from the anterior end, the
scar ranged from ventral number 115 to 122 (average, 119) in 28 females
and from number 117 to 126 (average, 121) in 14 males. The difference
between male and female cottonmouths is not nearly so great as in
_Heterodon_.
Later Growth and Bodily Proportions
The only records of growth increments in a natural population of
cottonmouths are those in Table 11. The period of growth is mostly the
period of activity, and differences are expected between northern and
southern populations. As size increases, determination of growth rate
becomes more difficult because age classes overlap in size. Growth of
any individual depends not only on climate and food but also on disease
and parasitism and the innate size potential. Stabler (1951:91) showed
weight and length relationships in two cottonmouths for a period of six
and one-half years.
TABLE 11.--Growth Increments in Cottonmouths (Barbour,
1956:38-39).
=============================================
| Number of | Total |Estimated| Estimated |
| | length | age | growth |
| | | | from |
| | | | preceding |
| | | | year |
|individuals| in |in months| in |
| |millimeters| |millimeters|
|-----------+-----------+---------+-----------|
| 19 | 260-298 | 7-8 | 25 |
| 11 | 312-337 | 19-20 | 45 |
| 40 | 355-485 | 31-32 | 95± |
| 83 | 500-1000 | 43-44+ | ? |
---------------------------------------------
My study failed to reveal any secondary sexual difference in growth rate
and maximum size. Of the 306 cottonmouths measured by me, 16 males and
five females exceeded 700 millimeters in snout-vent length. Two males
were more than 850 millimeters long. One cottonmouth lived in captivity
for 18 years and 11 months (Perkins, 1955:262). The maximum total
lengths were reported by Conant (1958:186-187) to be 74 inches (1876
mm.) in _A. p. piscivorus_ and 54 inches (1370 mm.) in _A. p.
leucostoma_.
[Illustration: FIG. 6. Head length (º) and head width (·) expressed as a
percentage of snout-vent length of living and preserved cottonmouths.
Head length was measured from the tip of the snout to the posterior end
of the mandible. Head width was measured across the supraocular scales,
since accuracy was greater than if measured at the posterior edge of the
jaw. No sexual dimorphism or geographical variation occurs in these
characters.]
Proportions of various parts of the body vary considerably depending on
age, size and, in some instances, sex. Heads are proportionately larger
in young than in adults (Fig. 6), as is true of vertebrates in general.
This larger head has survival value for the cottonmouth in permitting
more venom to be produced and in permitting it to be injected deeper
than would be the case if the proportions were the same as in adults.
Relative to the remainder of the snake the head is considerably larger
than in the copperhead (Fitch, 1960:108) and slightly larger than in the
rattlesnake, _Crotalus ruber_ (Klauber, 1956:152).
[Illustration: FIG. 7. Tail length expressed as a percentage of
snout-vent length of living and preserved cottonmouths (·--males;
º--females).]
In general, tails are relatively longer in males than in females of the
same size (Fig. 7), except that there is little or no difference at
birth. Growth of the tail in males proceeds at a more rapid rate. In
certain individuals sex cannot be recognized from length of the tail
relative to snout-vent length because overlapping occurs, especially in
medium-sized individuals. Similar changes of proportions with increase
in age occur in copperheads (Fitch, 1960:106) and rattlesnakes (Klauber,
1956:158-159), but the tail of the cottonmouth is relatively much
longer.
SHEDDING
The Shedding Operation
Shedding of the skin is necessary to provide for growth and wear in
snakes. The milkiness or bluing of the eyes, which causes partial
blindness, marks the initial stage of shedding and is caused by a
discharge of the exuvial glands that loosens the old _stratum corneum_
from the layer below. In four to seven days the opaqueness disappears,
and the snake sheds after an additional three to six days (Table 12).
Young snakes first shed within a few days after birth and generally shed
more frequently than adults, but the interval is variable. The eyes of
three young cottonmouths observed by Wharton (1960:126) became milky on
the fourth day but cleared on the seventh day, and the skin was shed on
the eighth day. The eyes of three young kept by me became milky two to
three days after birth, cleared on the seventh to tenth days, and the
skin was shed on the thirteenth day. Possibly the relatively long
interval in this instance resulted from low relative humidity in the
room where the snakes were kept. According to Fitch (1960:134), litters
of young copperheads usually shed within three to ten days after birth;
but under unusually dry conditions shedding did not occur for several
weeks.
TABLE 12.--Duration of Preparatory Period (in days) to Shedding
in 11 Cottonmouths.
==============================
|Duration | Time |Time from |
| of |between |beginning |
|cloudiness|clearing| of |
| | and |cloudiness|
|of eyes |shedding| until |
| | | shedding |
|----------+--------+----------|
| 5 | 6 | 11 |
| 7 | 3 | 10 |
| - | - | 6 |
| - | - | 6 |
| 5 | 3 | 8 |
| 4 | 6 | 10 |
| 7 | 3 | 10 |
| 5 | 6 | 11 |
| 5 | 3 | 8 |
| 7 | - | - |
| 7 | 3 | 10 |
| ---- | ----| ---- |
|[=X] 5.4 |[=X] 3.8| [=X] 9.0 |
------------------------------
Cottonmouths as well as other snakes usually do not feed until after the
skin is shed and are generally quiescent during the period preceding
shedding, except that immediately before shedding they become active and
rub their snouts on some rough object and may yawn several times
seemingly in an attempt to loosen the skin along the edges of the lips.
After the skin is loosened from the head, more rubbing against rough
surfaces and writhing serves to pull the old skin off, turning it inside
out. Once the old skin has passed over the thick mid-body, the snake
often crawls forward using rectilinear locomotion until the skin is
completely shed. It normally comes off in one piece; but, if the snake
is unhealthy or has not had sufficient food or water, the skin may come
off in patches. Frequently one or both of the lens coverings are not
shed immediately and impair the sight. Bathing or swimming ordinarily
causes dried skin to peel off; and, because of the cottonmouth's aquatic
habits, its chances of shedding successfully are much greater than those
of less aquatic snakes. Cottonmouths that have recently shed have bright
and glossy patterns, in contrast to the dull and dark appearance of
those that are preparing to shed.
Frequency of Shedding
Most of our knowledge concerning the frequency of shedding is based upon
observations of captives. It is known that the intervals between
exuviations are largely dependent upon the amount of food taken and the
rate of growth. Unless laboratory conditions closely resemble those in
the field, shedding frequencies in captives probably differ much from
those of free-living snakes.
Only two of my captives shed twice. The intervals between exuviations in
the two snakes were eight and five months, lasting from August to April
and from December to May, respectively. Ten other snakes shed once in
the period from January through July. Stabler (1951:91) presented data
concerning shedding of two cottonmouths kept 12 and 14 years in
captivity. One shed 25 times in 12 years and the other shed 37 times in
14 years, giving an average of 2.1 and 2.6 per year, respectively.
Neither of the snakes shed from December through March, but the period
of shedding corresponded to the period of greatest activity and growth.
In Florida, cottonmouths shed four to six times a year, according to
rate of growth (Allen and Swindell, 1948:7).
FOOD HABITS
Methods of Obtaining Prey
Food is obtained by a variety of methods depending on the type of food,
age of the cottonmouth, and possibly other factors. Some captives lie in
ambush and others crawl slowly in active search. At the first cue of
possible prey, either by sight, scent, or differential temperature
detection by the pit, the snake appears to become alert and flicks its
tongue out at fairly rapid intervals.
By means of the facial or loreal pit found in all crotalids, the snake
is able to detect objects having temperatures different from that of the
surroundings of the objects. In detecting prey the tongue acts to
sharpen the sense of "smell" by conveying particles to Jacobson's organs
in the roof of the mouth. On many occasions cottonmouths appeared to
rely solely on sight; they passed within a few inches of prey,
apparently unaware of its presence until it moved. When pools of water
begin to dry up toward the end of summer, cottonmouths often congregate
and feed on dying fish. In these instances the fish are usually taken as
they come to the surface. In laboratory observations moccasins seize
live fish and some moccasins carry the fish until they have received
lethal doses of venom; afterward the fish are swallowed. But grasping
and manipulation of the prey occurs without the fangs' being employed,
especially in the case of dead fish. On one occasion a cottonmouth was
observed to grasp the edge of a glass dish that had contained fish and
apparently retained the odor. On another occasion I placed several fish
in a bowl, rubbed a stick on the fish, and then touched each snake
lightly on the nose with the stick. The snakes crawled directly to the
bowl and began feeding. At other times these same snakes crawled around
the cage in an apparent attempt to locate the food but paid little
attention to fish held in front of them. If the catching of prey under
natural conditions were as uncoordinated as it sometimes is in
captivity, the snakes probably would not be able to survive.
Wharton (1960:127-129) described tail-luring in one individual of a
76-day-old brood of cottonmouths. The snake lay loosely coiled with the
tail held about six centimeters from the ground; a constant waving
motion passed posteriorly through the terminal inch of the tail. These
movements ceased at 7:20 p.m. but were resumed at 7:40 a.m. the
following day. All observations were under artificial light. The "caudal
lure" as a means of obtaining prey has been described in other species
and related genera by Neill (1960:194) and Ditmars (1915:424).
Various authors have suggested that the method of capture differs
according to the kind of prey. Allen and Swindell (1948:5) stated that
cottonmouths retain their hold after striking fish or frogs but will
release a mouse after delivering a bite and are timid in striking at
larger rodents. Neill (1947:203) noted that a cottonmouth always waited
several minutes after biting a large rat before approaching its prey.
This same type of behavior has been reported for copperheads (Fitch,
1960:194) and rattlesnakes (Klauber, 1956:618). Cottonmouths observed by
me retained a strong hold on fish, frogs, and sometimes mice, but almost
always released large mice and baby chicks, which were not eaten until
after death.
Different behavior according to type of prey is correlated with ability
of prey to retaliate, although some animals may not be released because
they could easily escape. For instance, a frog could hop far enough to
escape in a matter of seconds if released. A 73-millimeter _Rana
pipiens_ that I observed was bitten twice within one and a quarter hours
and died 45 minutes after the last bite. Its movement was uncoordinated
by the time of the second bite, but it could have escaped had the frog
not been confined. Although it is doubtful that normal, healthy fish are
frequently captured by cottonmouths, Allen (1932:17) reported that a
cottonmouth was seen pushing a small, dead pike about on the surface of
a stream. A wound on the belly of the fish indicated that it had been
bitten. A 17-gram creek chub (_Semotilus_) and a 13.7-gram bass
(_Micropterus_) were injected by me with one-fourth cubic centimeter of
fresh venom near the base of the tail in order to determine whether the
fish could escape after being bitten and released. The creek chub
flipped onto its back after a minute and 45 seconds and gill movements
stopped in eight minutes and 35 seconds; the bass flipped over after 50
seconds and died in two minutes and 10 seconds. The venom immediately
affected both fish, and it is unlikely that either could have swum more
than a few feet.
After its prey has been killed, a cottonmouth examines the body from end
to end by touching it with the tongue. Then the animal is grasped in the
mouth without the use of the fangs and is slowly manipulated until one
end (usually the head) is held in the mouth. The lengthy process of
swallowing then takes place, the fangs and lower jaws alternately
pushing the prey down the throat.
Food and Food Preferences
The cottonmouth seems to be an opportunistic omni-carnivore, because it
eats almost any type of flesh that is available, including carrion. It
feeds primarily upon vertebrates found in or near water; but
invertebrates and eggs have also been found in the diet. The only
potential prey items that seem not to be normally eaten are bufonid
toads and tadpoles. I have occasionally offered tadpoles and frogs to
cottonmouths, but only the frogs were accepted. But, Stanley Roth kept a
cottonmouth in captivity that ate both toads and tadpoles. If tadpoles
are commonly eaten, their probable rapid digestion would make
identification almost impossible.
Following is a list of known foods of the cottonmouth:
Captivity: "... rattlesnake.... The same moccasin also killed
and ate a smaller snake of its own species...." (Conant,
1934:382.)
Florida: "3 heron feathers, bird bone, _Eumeces inexpectatus_,
3 fish all under one inch in length, 1 heron egg shell" (Carr,
1936:89). According to Allen and Swindell (1948:5), "the food
included other moccasins, prairie rattlesnakes, king-snakes,
black snakes, water snakes, garter snakes, ribbon snakes, and
horn snakes ... most of the species of frogs, baby alligators,
mice, rats, guinea pigs, young rabbits, birds, bats, squirrels,
and lizards ... a mud turtle ... a case of a four footer eating
ten to twelve chicken eggs. The most common food appears to be
fish and frogs. Catfish are included on this list...." Yerger
(1953:115) mentions "an adult yellow bullhead, _Ameiurus
natalis_ ... 306 mm. in standard length [from a 63-inch
cottonmouth]."
Georgia: "... full grown _Rana catesbeiana_, several foot-long
pickerel ... dead fish if placed in a pan of water.... _Natrix
sipedon fasciata_ and _Masticophis flagellum_ ... rats....
Toads and large _Eumeces laticeps_ were always ignored."
(Neill, 1947:203.) "_Natrix_, _Heterodon_, _Kinosternon_,
_Rana_, _Hyla cinerea_, _Microhyla_, Microtine [_Pitymys
pinetorum_]." (Hamilton and Pollack, 1955:3.)
Mississippi: "... _Hyla gratiosa_.... In captivity specimens
have eaten frogs, mice, birds, dead fish, pigmy rattlers and
copperheads. Toads ... were refused" (Allen, 1932:17). One
moccasin "disgorged a smaller decapitated moccasin ... killed
the day before by boys" (Smith and List, 1955:123).
Tennessee: "Beetles in one stomach; lizard (_Eumeces_) in
another stomach; small snake (_Natrix_) in one intestine, and
hair in another intestine. One stomach contained numerous bits
of wood, up to four inches in length...." (Goodman, 1958:149.)
Kentucky: "_Siren intermedia_ was the most abundant food item
in both volume and occurrence. Frogs of the genus _Rana_ ranked
second. Together, these two items comprised almost 2/3 of the
food of the snakes. The other food items were distributed among
the fishes, reptiles, and other amphibians [one _Rana_ tadpole
included]." (Based on 42 samples--Barbour, 1956:37.)
Illinois: (Based on 84 samples--Klimstra, 1959:5.)
_Per cent Frequency_ _Per cent_
_Food Item_ _of Occurrence_ _Volume_
Pisces 39.3 31.9
Amphibia 36.9 26.0
Reptilia 25.0 18.2
Mammalia 30.9 17.9
Gastropoda 17.8 1.0
Miscellaneous 25.0 5.0
(Algae, Arachnida,
Aves, Insecta)
Louisiana: Penn (1943:59) mentions that a "female had just
eaten two young cottonmouths...." Clark (1949:259) mentions
"100 specimens--34 fish; 25 _Rana pipiens_; 16 _Rana
clamitans_; 7 _Acris_; 4 _Natrix sipedon confluens_; 8 birds; 5
squirrels ... catfish thirteen and one-half inches in length
... small-mouth black bass [eleven inches]."
Oklahoma: Force (1930:37) remarks that the moccasin "eats
bullfrogs ... but refuses leopard frogs." Trowbridge (1937:299)
writes: "several sun perch.... Another had eaten six catfish
six to ten inches long ... a water snake (_Natrix s.
transversa_) about 18 inches long ... frogs, mostly _Rana
sphenocephala_." Carpenter (1958:115) mentions "a juvenile
woodthrush.... Seven last instar cicadas ... a young
cottontail." According to Laughlin (1959:84), one moccasin
"contained the following items: 18 contour feathers of a duck,
probably a teal; one juvenile cooter turtle, _Pseudemys
floridana_; and a large mass of odd-looking unidentifiable
material. The other cottonmouth contained one juvenile pond
turtle, _Pseudemys scripta_...."
Texas: "... several ... feeding on frogs.... One ... found DOR
was found to contain a large catfish." (Guidry, 1953:54.)
Of 246 cottonmouths that I examined for food items, only 46 contained
prey in their digestive tracts. Almost all of the snakes examined were
museum specimens that had been collected at many places over a period of
about 40 years. It was not known how long each had been kept alive
before being preserved. Therefore it was impossible to determine what
proportion of any population of cottonmouths could be expected to
contain food. The food items were not analyzed numerically because the
scales and hair, by means of which many food items in the intestine were
identified, yielded no clue as to the number of individuals actually
present unless several distinct kinds were found. Each occurrence of
scales or hair was thus recorded as a single individual, although some
such occurrences may have represented more than one animal. The contents
of some stomachs were so well digested that it was difficult to
determine the number of items present. As a rule only one food item was
present in a digestive tract, but a few tracts contained several items
of the same or different species. Three frogs (_Acris crepitans_) were
in one snake and three hylas (_Hyla versicolor_) in another. Still
another individual captured beside a drying pond contained six
individuals of _Lepomis_ each about three inches long and two pikes
(_Esox_) about six inches long.
TABLE 13.--Analysis of Food Items of 46 Cottonmouths Collected
in Arkansas, Louisiana, and Texas (1922-1962).
===========================+========+==========+=========+==========
| | Number | Percent |Estimated|Estimated |
| | of | | | |
| |samples |frequency | weight |percentage|
| | in | | | |
| FOOD ITEMS | which | of | in | by |
| | item | | | |
| |occurred|occurrence| grams | bulk |
|---------------------------+--------+----------+---------+----------|
|Fish | (7) | 13.2 | 20 | 18.4 |
| _Esox_ sp. | 1 | | | |
| _Lepomis_ sp. | 2 | | 15 | |
| Unidentified | 4 | | | |
|Amphibians | (12) | 23.0 | | 20.4 |
| _Scaphiopus hurteri_ | 1 | | 13 | |
| _Acris crepitans_ | 2 | | 4 | |
| _Hyla cinerea_ | 2 | | 12 | |
| _Hyla versicolor_ | 1 | | 12 | |
| _Rana catesbeiana_ | 1 | | 20 | |
| _Rana pipiens_ | 3 | | 15 | |
| Unidentified | 2 | | | |
|Reptiles | (15) | 28.4 | | 29.9 |
| _Pseudemys scripta_ | 2 | | 15 | |
| _Anolis carolinensis_ | 1 | | 6 | |
| _Eumeces fasciatus_ | 1 | | 7 | |
| _Lygosoma laterale_ | 2 | | 5 | |
| _Natrix_ sp. | 1 | | 10 | |
| _Natrix erythrogaster_ | 2 | | 10 | |
| _Agkistrodon piscivorus_ | 2 | | 20 | |
| _Crotalus_ sp. | 1 | | 30 | |
| Unidentified snakes | 3 | | | |
|Birds | (4) | 7.6 | | 18.6 |
| _Anhinga anhinga_ (juv.) | 1 | | 60 | |
| Egret (head and neck) | 1 | | 20 | |
| Passeriformes | 2 | | 20 | |
|Mammals | (6) | 11.3 | | 12.7 |
| _Blarina brevicauda_ | 1 | | 12 | |
| Cricetinae | 5 | | 18 | |
|Unidentified | (9) | 17.0 | | |
---------------------------+--------+----------+---------+-----------
The "unidentified" category (Table 13) refers to jellylike masses in the
stomach or material in the intestine in which no scales, feathers, hair,
or bones could be found. Most of the unidentifiable matter could be
assumed to consist of remains of amphibians, since they leave no hard
parts. If this assumption is correct, amphibians comprise about 40 per
cent of the diet. Since intestinal contents were included, a volumetric
analysis was not feasible. Therefore, the weight of each type of food
item was estimated and the percentage by bulk calculated from it (Table
13).
Pieces of dead leaves and small sticks constituted most of the plant
material found and presumably were ingested secondarily because they
adhered to the moist skin of the prey, especially to fish and
amphibians. However, some plant materials probably are eaten because
they have acquired the odor of the prey. One cottonmouth contained a
_Hyla cinerea_, several leaves, and five sticks from 37 to 95
millimeters long and from 12 to 14 millimeters in diameter.
Most reports in the literature state that gravid females do not feed,
but four gravid females examined by me containing large, well-developed
embryos also contained evidences of having recently fed. Two of them had
scales of snakes in the stomach or intestine, one contained a six-inch
_Lepomis_, and the other had hair in the intestine and the head and neck
of an adult egret in the stomach.
MORTALITY FACTORS
Natural Enemies and Predators
Published records of other animals preying on cottonmouths or killing
them are few. Reptiles more often than other classes of vertebrates prey
on the cottonmouth. McIlhenny (1935:44) reported on the scarcity of
snakes in areas where alligators were present. Predation on cottonmouths
by indigo snakes (_Drymarchon corais_) was reported by Conant (1958:153)
and Lee (1964:32). Allen and Swindell (1948:6) obtained a photograph of
a king-snake (_Lampropeltis getulus_) killing a cottonmouth but thought
that moccasins are not eaten by _L. getulus_. However, one occasion
reported herein shows that cottonmouths are eaten by king-snakes; and
Clark (1949:252) reported finding 13 cottonmouths, along with other
prey, in the stomach contents of 301 king-snakes (_L. g. holbrooki_)
from northwestern Louisiana. Cannibalism is also common among
cottonmouths. Klauber (1956:1058;1079) cited predation on cottonmouths
by a blue heron (_Ardea herodias_) and a largemouth bass (_Micropterus
salmoides_). Man is probably the greatest enemy of the cottonmouth.
Intentional killing, capturing, road kills, and alteration of the
environment destroy large numbers.
Parasites and Diseases
Allen and Swindell (1948:12) listed several diseases and parasites of
snakes and stated that "some moccasins captured in the woods are so poor
and weak from parasitic infection that they can barely crawl." The only
kind of ectoparasite found on captive cottonmouths in the course of my
study was a snake mite, _Ophionyssus natricus_. An infestation of that
mite was thought to be partly responsible for the death of one captive
moccasin. Other moccasins spent increasing amounts of time in their
water dish after they became infected with mites. Under natural
conditions frequent swimming probably keeps cottonmouths nearly free of
mites.
Endoparasites found included lung flukes, stomach nematodes, and
tapeworms. Lung flukes (_Ochetosoma_ sp.) were found in 16 of 20 captive
cottonmouths. Snails and frogs serve as intermediate hosts for various
stages in the life cycle of these flukes. The high percentage of
cottonmouths infested with flukes is indicative of the use of frogs as a
major source of food. Less than ten flukes were usually observed in the
snakes' mouths but occasionally more were seen. One snake was observed
thrashing about in its cage for nearly an hour, after which time it
died. Upon examination of the mouth, 32 flukes were found, most of which
were located in the Jacobson's organs. Whether or not flukes caused the
death is not known. Nematodes (_Kalicephalus_ sp.) were found in the
stomach of each of several preserved specimens; most of these snakes had
no food in their digestive tracts. In a high percentage of the
moccasins, tapeworms (_Ophiotaenia_ sp.) were in the duodenum, in many
instances so tightly packed as seemingly to prevent passage of food. The
importance of fish in the diet is reflected by the high percentage of
snakes containing tapeworms. An unidentified cyst (?) about an inch long
and containing two hooks on one end was found attached to the outer wall
of the stomach of a cottonmouth. Yamaguti (1958) listed all the kinds of
helminths known from cottonmouths.
Miscellaneous Causes of Death
Munro (1949:71-72) reported on the lethal effect of 10 per cent DDT
powder on two young cottonmouths which were dusted with it to kill
mites. Herald (1949:117) reported an equal effect caused by spraying a
five per cent DDT solution in a room with several snakes. All but three
large cottonmouths, which were under shelter at the time of spraying,
were killed.
One individual that refused to eat was dissected soon after death, and a
short piece of a branch on which two large thorns were located at 90°
angles was found blocking the intestine at the posterior end of the
stomach.
An unexpected and probably unusual circumstance caused the death of two
captives. After cleaning a cage containing five cottonmouths and placing
several mice in the cage for food, I noticed two of the snakes lying
stretched out, partially on one side, and almost unable to move. At
first I thought they had been bitten by other snakes which were in
pursuit of the mice. The two died after two days. When a similar
incident occurred in another cage, I removed the "bitten" snake and it
fully recovered after 11 days. When the same symptoms were observed in a
garter snake in another cage, I realized that in each instance the cage
had been cleaned and fresh cedar chips placed in it immediately prior to
observation of these symptoms. Fine cedar dust on the chips had
evidently poisoned the snakes.
BEHAVIOR
Annual and Diel Cycles of Activity
In the days following emergence in spring, cottonmouths often endure
uncomfortable and even dangerous temperatures in order to obtain food
and mates. They are more sluggish at this time and more vulnerable to
predation than later in the season when temperatures are optimal. Fitch
(1956:463) found that copperheads in northeastern Kansas begin their
annual cycle of activity in the latter part of April, when the daily
maximum temperature is about 22° C. and the minimum is about 4° C., and
become dormant in late October or early November, at which time the
daily maximum temperature is about 15° and the minimum is about 0°.
Indications are that in the northern part of its range the annual
activity cycle of the cottonmouth resembles that of the copperhead in
northeastern Kansas. Klimstra (1959:2) captured cottonmouths from April
to October in southern Illinois. Barbour (1956:36) collected large
numbers of them in early April in Kentucky and stated that they migrate
from swamps to wooded hillsides in late August and early September.
Spring migrations begin after a few consecutive warm days in March. In
northern Oklahoma cottonmouths have been found along the Verdigris River
as early as March, suggesting that a few winter in crayfish holes and
mammal burrows. The majority of individuals found in this area were at
denning sites along cliffs above the river and emerged later than those
near the river (Dundee and Burger, 1948:1-2). In Virginia cottonmouths
have been seen as early as March 5 (Martin and Wood, 1955:237) and as
late as December 4. They have been observed in migration from the swamps
of the barrier beach to the mainland in late October and early November
in southeastern Virginia (Wood, 1954a:159). According to Neill
(1947:204), the cottonmouth tolerates lower temperatures than do most
snakes in Georgia and is one of the last to go into hibernation. Allen
and Swindell (1948:4) stated that cottonmouths usually bask during the
mornings of the cooler months in Florida, but they mentioned nothing of
denning such as occurs farther north. Although winter aggregations occur
in the northern parts of the range, I have never seen such aggregations
in the South. However, in one instance related to me by a reliable
observer, seven cottonmouths were found together on a creek bank near
the Gulf Coast in early spring.
During late summer and early autumn, fat is deposited in lobes in the
lower abdomen in preparation for the period of winter quiescence. Gravid
females usually do not feed so frequently or so much as other snakes,
because they tend to become inactive as the ova develop. Whether or not
females feed heavily after parturition and previous to denning is not
known. Peaks of activity in autumn may be caused by final attempts to
feed before denning and by the appearance of large numbers of newborn
young. The young usually have from one to two months in which to feed
before the advent of cold weather. According to Barbour's (_op.
cit._:38) findings, the young probably feed before hibernation because
they grow substantially in winter. For those that do not feed, the rate
of survival is perhaps much lower.
In preparation for winter, cottonmouths migrate inland, usually to dry
forested hillsides where they den, commonly among rocks at the tops of
bluffs, along with several other species of snakes. In such aggregations
there is no hostility and each individual may derive benefit from
contact with others by which favorable conditions of temperature and
humidity are maintained.
Neill (1947:204) has found many specimens in winter by tearing bark from
rotting pine stumps on hillsides overlooking lakes or streams. On cold
days they evidently retreat below the surface, while on warm days they
lie just below the bark or emerge and bask. Neill believes that the use
of stumps by cottonmouths is an innate pattern of behavior, because of
the large number of young-of-the-year found in such surroundings.
Cottonmouths were observed in winter also under logs and stumps by Allen
(1932:17). I have twice observed cottonmouths crawling into crayfish
burrows along the Gulf Coast of Texas, and suppose they are used as
denning sites to some extent.
The diel cycle of activity of cottonmouths is of necessity closely
related to the seasonal cycle. Since optimal temperatures determine
activity, the diel cycle varies greatly from time to time. It has been
well established that cottonmouths, like most other crotalids and many
snakes of other families, prefer nocturnal to diurnal activity, even
though the temperature may be less favorable at night. This preference
is correlated with increased nocturnal activity of frogs and reptiles
that constitute the principal food supply.
During spring and autumn, activity is more restricted to the day and
long periods of basking occur. However, as hot weather approaches,
basking occurs mainly in the morning and evening and activity becomes
primarily nocturnal. But, in well shaded, moist forests, cottonmouths
feed actively in the daytime.
Availability of food also has an important influence upon activity.
Allen and Swindell (_op. cit._:5) stated that moccasins congregate
around drying ponds and feed on dying fish until the moccasins can hold
no more. They then usually stay nearby as long as food remains. In an
area of the Stephen F. Austin Experimental Forest near Nacogdoches,
Texas, many cottonmouths journey daily to and from a swamp and a dry
field, evidently to feed on rodents inhabiting the area. Ten individuals
captured along a snake-proof fence that was built 30 yards from the
swamp were found lying coiled along the fence after 4:30 p.m., at which
time the area was shaded. On another occasion, I captured a large
cottonmouth that was feeding upon dying fish in a drying pool about
10:30 a.m. on August 19, 1962.
Because of the aquatic habits of the cottonmouth, relative humidity
probably has little influence on the snake's activity. However,
cottonmouths are more restricted to the vicinity of water in dry weather
than during rains or muggy weather when many of their natural prey
species also move about more freely. Increased activity on cloudy days
may result from protection from long exposure to sunshine. Torrential
rains and floods, such as those following hurricanes along the Gulf and
Atlantic coasts of the southeastern United States, bring out quantities
of snakes of all species. Rattlesnakes and cottonmouths in particular
are killed by the thousands at these times because they seek shelter in
human habitations. However, these are unusual circumstances and do not
reflect voluntary activity as a result of preferences.
Thermal reactions of reptiles were classified by Cowles and Bogert
(1944) into several categories. For each species there is a basking and
normal activity range limited by the voluntary minimum and voluntary
maximum at which the animal seeks shelter. Beyond this normal range are
the critical thermal minimum and critical thermal maximum (C. T. M.) at
which effective locomotion is prevented. The lethal minimum and maximum
are those temperatures at which short exposure produces irreparable
damage, and death inevitably results. These classifications are modified
somewhat by seasonal or laboratory acclimation or by the physiological
state of the animal. The C. T. M. of five cottonmouths was determined by
placing each individual in an enclosed area and heating it with an
infrared lamp. Cloacal temperatures were taken with a Schultheis
quick-recording thermometer as soon as the snake could no longer right
itself when placed on its back. All temperatures were in degrees
Celcius. The C. T. M. averaged 39.2° (38.0° to 40.0°). A temperature of
38.0° was lethal to one individual. These cottonmouths had been in
captivity for nine months. The behavior of the snakes during heating
resembled those instances described by Klauber (1956:382-387) for
rattlesnakes. As the body temperature of the snakes rose past the
optimum, each individual became disturbed and tried to escape from the
enclosure. The snakes soon became frantic in their efforts to escape.
After about five minutes the mouth was opened and heavy, slow breathing
was begun, accompanied by a loss of coordination and a slowing down of
movements. The snakes writhed spasmodically for a few seconds and then
lay still, usually with the mouth open. Recovery was begun by rolling on
the belly and flicking the tongue, followed by movements of the head and
then the body. Cottonmouths are rarely exposed to dangerously high
temperatures owing to their semi-aquatic habits, but there are probably
occasions when individuals reach the C. T. M. for the species.
Basking
Since activity, digestion, and gestation depend upon adequate internal
temperatures, there must be a process by which these temperatures are
attained and for an appropriate time maintained. Basking is important in
this respect. The cottonmouths prefer to lie in a coiled position and,
during basking, can usually be found beside bodies of water or on
branches of dead trees overhanging the water. They are good climbers and
have a prehensile tail that is frequently employed in descending from
small branches. Since cottonmouths are semi-aquatic and are often
exposed to temperatures that are lower than those of the air, they
either must bask more often than terrestrial snakes or tolerate lower
temperatures. Length of the period of basking is determined not only by
amounts of insolation and temperature but also by the size of the snake.
A smaller snake can reach its optimum temperature more rapidly because
of a higher surface-to-volume ratio. Another factor that may play a
minor role in the rate of temperature change is the color of the snake.
The wide variation in color of cottonmouths probably affects rates of
heat increase and loss due to direct radiation. Slight hormonal control
of melanophores described in snakes by Neill and Allen (1955) also may
exert some influence on the length of time spent basking. No rates of
temperature increase or decrease are available for cottonmouths.
Coiling
While inactive the cottonmouth spends most of its time lying in a coiled
position with the tail outermost, with the body usually wound into about
one and one-half cycles, and the head and neck in a reversed direction
forming a U- or S-shaped loop. From this position the snake is able to
make a short strike or a hasty getaway if necessary. In my opinion this
position is used primarily for basking or resting and only secondarily
for feeding. Most individuals appear to pursue their prey actively, not
lying in ambush for the approaching prey to the extent that most other
crotalids do.
Many of the cottonmouths that I kept in captivity were observed in a
coiled position for periods up to three or four days. Under natural
conditions, however, they are more active. Young cottonmouths are
inclined to remain in a coiled position for longer periods than older
individuals.
Locomotion
Four distinct types of locomotion have been described in snakes:
horizontal undulatory, rectilinear, sidewinding, and concertina
(Klauber, 1956: 331-350). Most snakes are capable of employing two or
more of these types of progression, at least to a certain degree; but
horizontal undulatory locomotion is the most common method used by the
majority of snakes, including the cottonmouth. In this method the
snake's body is thrown into lateral undulations that conform with
irregularities in the substrate. Pressure is exerted on the outside and
posterior surface of each curve, thus forcing the body forward.
Rectilinear locomotion is more useful to large, thick-bodied snakes
which use this method of progression, chiefly when they are prowling and
unhurried. This method depends upon the movement of alternate sections
of the venter forward and drawing the body over the ventral scales
resting on the substratum by means of muscular action. This mode of
locomotion was most frequently observed in captive cottonmouths when
they were crawling along the edge of their cages, especially when they
were first introduced to the cages and toward the end of the shedding
process. The other two types of locomotion, sidewinding and concertina,
have not, to my knowledge, been observed in the cottonmouth.
Both the cottonmouth and the cantil have definite affinities for water
and are as likely to be found in water as out of it. Copperheads and
rattlesnakes, although not aquatic, are good swimmers. When swimming, a
motion resembling horizontal undulatory progression is used.
Disposition
The number of different opinions expressed in the literature concerning
the cottonmouth's disposition is not at all surprising. As with any
species there is a wide range of individual temperament, which is
affected by many factors. The cottonmouth is considered by some writers
to be docile while others consider it to be highly dangerous. Allen and
Swindell (1948:7) described the variability in temperament, even among
individuals. They wrote: "On rare occasions, moccasins are found which
will attack. A perfectly docile snake will turn and bite viciously
without any apparent reason." They also recounted a case in which a
cottonmouth was kept as a pet for six years, being allowed the freedom
of the house. Smith and List (1955:123) found them "... surprisingly
docile in the gulf region [Mississippi], displaying none of the
pugnacity of more northern cottonmouths." Smith (1956:310) stated:
"Unlike the copperhead, cottonmouths are pugnacious; their powerful
jaws, long fangs, vicious disposition and potent venom make them a very
dangerous animal."
My own observations are in general agreement with the statements of
Allen and Swindell (_loc. cit._). In my encounters with cottonmouths, I
have never found any aggressive individuals except for three juveniles
that were born in captivity. In their first three days in the laboratory
these juveniles were observed to strike repeatedly whenever anyone
entered the room. After this short period of aggressiveness, however,
they slowly became more docile. The disposition shown by the newborn
young is clearly an innate behavioral pattern that undoubtedly has a
direct relationship to survival. The majority of cottonmouths that I
have approached in the field have moved swiftly to seek refuge in nearby
water; a few have remained motionless as I approached, and one showed
the typical threat display. Upon capture and handling, they react
similarly to other pit-vipers by opening and closing the mouth and
erecting the fangs in an attempt to bite. They often bite through the
lower jaw and eject venom at this time as well as when the mouth is
open. Of more than a dozen individuals kept in captivity, four were
particularly difficult to handle whereas another was extremely docile.
It was almost never found in aggregations with the other snakes and did
not struggle or attempt to bite when handled. The majority remained
unpredictable in disposition, usually appearing docile and lazy but
capable of extremely rapid movements when disturbed.
Defense and Escape
The typical threatening posture of rattlesnakes is all but lacking in
the cottonmouth, which relies primarily on concealing coloration or
nearness to water for escape. When approached, it usually plunges into
nearby water or remains motionless with the head held up at a 45° angle
and the mouth opened widely exposing the white interior. The tail is
sometimes vibrated rapidly and musk is expelled. This threat display is
unique to cottonmouths; although it does not attract as much attention
as the display of rattlesnakes, it is probably an effective warning to
most intruders at close range.
Neill (1947:205) reported one case in which a cottonmouth used the "body
blow" defense, described for _Crotalus_ by Cowles (1938:13), when
approached by a king-snake, _Lampropeltis getulus_. In this unusual
posture the anterior and posterior portions of the body are held against
the ground and the middle one-fourth to one-third of the body is lifted
up and used in striking the intruder. This same defense posture also was
observed in rattlesnakes when presented with the odor of the spotted
skunk, _Spilogale phenax_. However, the "king-snake defense posture" is
probably not a well-established behavioral pattern in the cottonmouth,
for it sometimes feeds upon king-snakes. I observed the killing and
devouring of a cottonmouth by a speckled king-snake, _L. g. holbrooki_;
the only attempts to escape were by rapid crawling and biting.
Cottonmouths often squirt musk as a defensive action. The tail is
switched back and forth, and musk is emitted from glands on each side of
the base of the tail. The fine jets of musk are sprayed upward at about
45° angles for a distance of nearly five feet. How often this defense
mechanism is used against other animals is not known, but the musky odor
can frequently be detected in areas where cottonmouths are common. The
odor is repulsive and, if concentrated, can cause nausea in some
individuals. To me, the scent is indistinguishable from that of the
copperhead.
"Head Bobbing"
"Head bobbing" in snakes has been described frequently in the
literature, and many interpretations have been advanced to explain its
occurrence. One of the earlier accounts was that of Corrington (1929:72)
describing behavior of the corn snake, _Elaphe guttata_. Characteristic
bobbing occurred when the snake was cornered, and seemingly the purpose
was to warn or frighten foes. Neill (1949:114-115) mentioned the jerking
or bobbing of the head in several species of snakes including the
cottonmouth, and remarked that "it is apparently connected with
courtship and with the recognition of individuals." According to Munro
(1950:88), "head bobbing" appears to be a sign of annoyance in some
instances but is usually concerned with reproduction and individual
recognition. Richmond (1952:38) thought that many types of head
movements among not only reptiles but also birds and some mammals are a
result of poor vision and serve "to delimit and orient an object that
for lack of motion is otherwise invisible." Head movements undoubtedly
occur in animals to facilitate accommodation, but it is obvious from
Richmond's conclusions that he has never observed "head bobbing" in
snakes. The term itself is grossly misleading and should be discarded.
Mansueti (1946:98) correctly described the movements as spastic
contractions of the body. I have observed numerous instances of these
movements in cottonmouths, copperheads, and rat snakes (_Elaphe
obsoleta_); and in no case has the movement resembled a head bob as is
described in lizards and other animals. The movement appears to be a
result of a nervous or sexually excited state and consists of highly
spastic contractions confined to the anterior part of the snake most of
the time but affecting the entire body on some occasions.
I found the response to be most common among cottonmouths in confinement
when food was introduced to a cage containing several individuals
(increasing the tendency to strike at a moving object) and when an
individual was placed back in the cage after being handled. At these
times the snakes that were inactive began to jerk for a few seconds.
When the snake is in this seemingly nervous state, the same response is
elicited by another snake crawling over it. At other times the movement
of one individual causes no such response. The jerking movements appear
to be released by the recognition of a nervous state in another
individual and may serve to protect the jerking individual from
aggressive advances of the former.
Where courtship is involved, the jerking motions are made in conjunction
with writhing of the male and do not result from the same type of
releaser described above.
Combat Dance
The so-called combat dance between male snakes has long been known, but
its significance is still poorly understood. It was for many years
believed to be courtship behavior until the participants were examined
and found to be males. Carr and Carr (1942:1-6) described one such
instance in two cottonmouths as courtship. In their observations, as
well as those of others, copulation was never observed following the
"dance" but was assumed to be the ultimate goal. After the discovery
that only males participated, it was suggested that combat involved
competition for mates, but the "dance" has been observed at times other
than the breeding season (Ramsey, 1948:228).
Shaw (1948:137-145) discussed the combat of crotalids in some detail but
drew no conclusions as to the cause of the behavior. Lowe (1948:134)
concluded with little actual evidence that combat among male snakes is
solely for territorial purposes. Shaw (1951:167) stated that combat may
occur as a possible defense against homosexuality. One case of
homosexual mating among cottonmouths was reported (Lederer,
1931:651-653), but the incomplete description seems to be of normal
courtship procedure except that the "female" tried to avoid the male.
Two instances of combat observed between timber rattlesnakes (_C. h.
horridus_) by Sutherland (1958:23-24) were definitely initiated because
of competition for food. More observations are needed before the
significance of the combat can be fully understood.
THE VENOM
Properties of the Venom
The venom and poison apparatus have developed primarily as a means of
causing rapid death in small animals that are the usual prey. As a
protective device against larger enemies, including man, the venom may
have some value; but this was probably unimportant in the evolution of
the poison mechanism. A secondary function of the venom is to begin
digestion of tissues of the prey. Since food is swallowed whole,
injection of digestive enzymes into the body cavity enhances digestion
of the prey.
Kellogg (1925:5) described venom as a somewhat viscid fluid of a
yellowish color and composed of 50 to 70 per cent proteins, the chief
remaining components being water and carbohydrates, with occasional
admixtures of abraded epithelial cells or saprophytic microorganisms.
Salts, such as chlorides, phosphates of calcium, magnesium, and
ammonium, occur in small quantities. Each of the components of snake
venom has a different effect on the body of the victim. It was at first
believed that there were two types of venoms: neurotoxic, which acts
upon nervous tissue; and haemotoxic, which acts on blood and other
tissues. It has since been found that venoms are composed of varying
mixtures of both types. Fairley (1929:301) described the constituents of
venom as: (1) neurotoxic elements that act on the bulbar and spinal
ganglion cells of the central nervous system; (2) hemorrhagins that
destroy the lining of the walls of blood vessels; (3) thrombose,
producing clots within blood vessels; (4) hemolysins, destroying red
blood corpuscles; (5) cytolysins that act on leucocytes and on cells of
other tissues; (6) elements that retard coagulation of the blood; (7)
antibactericidal substances; and (8) ferments that prepare food for
pancreatic digestion. Elapid snakes tend to have more of elements 1, 4,
and 6 in their venoms, while viperids and crotalids, of which the
cottonmouth is one, have higher quantities of elements 2, 3, and 5.
Kellogg (_loc. cit._) stated that venom of cottonmouths contains more
neurotoxin than that of rattlesnakes and not only breaks down the nuclei
of ganglion cells but also produces granular disintegration of the
myelin sheath and fragmentation of the conducting portions of nerve
fibers.
Thus, venoms contain both toxic elements and non-toxic substances that
promote rapid spreading of the venom through the body of the victim.
Jacques (1956:291) attributed this rapid spreading to the hyaluronidase
content of venoms.
Venom Yield and Toxicity
One of the most important yet undeterminable factors of the gravity of
snakebite is the amount of venom injected into the victim. Since this
volume varies considerably in every bite, attempts have been made to
determine the amount and toxicity of venom produced by each species of
poisonous snake. Individual yield is so variable that a large number of
snakes must be milked in order to determine the average yield. Even then
there remains an uncertainty as to how this amount may compare with that
injected by a biting snake.
Wolff and Githens (1939b:234) made 16 venom extractions from a group of
cottonmouths in a two-year period. The average yield per snake
fluctuated between 80 and 237 milligrams (actual weight), and toxicity
measured as the minimum lethal dose for pigeons varied from 0.05 to 0.16
milligrams (dry weight). No decrease in yield or toxicity was evident
during this period. Another group of cottonmouths from which venom was
extracted over a period of five years also showed no decrease in yield
or toxicity. Of 315 individual extractions the average amount obtained
from each individual was 0.55 cubic centimeters of liquid or 0.158 grams
of dried venom (28.0 per cent solids). The minimum lethal dosage (M. L.
D.) which was determined by injecting intravenously into 350-gram
pigeons was found to be 0.09 milligrams (dry weight). Each snake carried
approximately 1755 M. L. D.'s of venom.
The record venom extraction for the cottonmouth was 4.0 cubic
centimeters (1.094 grams dried venom) taken from a five-foot snake which
had been in captivity for 11 weeks and milked five weeks earlier (Wolff
and Githens, 1939a:52). The average yield of venom of cottonmouths is
about three times the average yield reported for copperheads by Fitch
(1960:256), a difference correlated with the greater bulk and relatively
large head of the cottonmouth.
Allen and Swindell (1948:13) stated that cottonmouth venom rates third
in potency, compared drop for drop to that of _Micrurus fulvius_ and
_Crotalus adamanteus_. Freshly dried cottonmouth venom tested on young
white rats showed the lethal dose to be from 23 to 29 milligrams per
kilogram of body weight. The venom of 11 one-week-old cottonmouths was
found to be more potent than that of adult males. Githens (1935:171)
rated _C. adamanteus_ venom as being weaker than that of the copperhead
(_A. contortrix_), which he rated only slightly lower than cottonmouth
venom. The crotalids which he ranked more toxic than cottonmouths are:
the Pacific rattlesnake (_C. viridis oreganus_) and the massasauga (_S.
catenatus_). He found _A. bilineatus_, _C. durissus_, and _C. v.
lutosus_ to have the same toxicity as cottonmouths. Minton (1953:214)
found that the intraperitoneal "lethal dose 50" (the dose capable of
killing half the experimental mice receiving injections of it) was 6.36
milligrams per kilogram for copperheads. However, in later publications
Minton (1954:1079; 1956:146) reported that the "lethal dose 50" for
copperheads was 25.65 milligrams. Approximately the same potency was
determined for cottonmouths. Several rattlesnakes that he tested showed
a higher toxicity than copperheads or cottonmouths.
Criley (1956:378) found the venom of copperheads to be 6.95, nearer
Minton's earlier estimate, and rated cottonmouth venom as being twice as
toxic as that of copperheads. The relative toxicities of other crotalids
tested, considering the cottonmouth to be one unit, were: _C.
basiliscus_, 0.3; _A. contortrix_, 0.5; _C. viridis oreganus_, 1.4; _A.
bilineatus_, 2.2; _C. adamanteus_, 2.3; _C. v. viridis_, 3.2; _C.
durissus terrificus_, 27.5.
It can be seen from the above examples that toxicity of venoms and the
resistance of the animal receiving an injection of venom is highly
variable. Possibly the venom of each species of snake has greatest
effect on animals of the particular group relied on for food by the
snake. If that is so, the venom of cottonmouths would be expected to be
more toxic when tested on fish, reptiles, and amphibians than on birds
and mammals. Likewise, the venom of most species of rattlesnakes would
be expected to be more virulent when injected into mammals than when
injected into lower vertebrates. But, according to Netting (1929:108),
species of rattlesnakes that prey on cold-blooded animals, which are
less susceptible to venoms than warm-blooded animals, are thought to
have highly toxic venoms. This explanation accounts for the powerful
venom of _Sistrurus catenatus_; and, in this respect, venom of
cottonmouths should be highly toxic also. However, no clear-cut trends
have been shown in most cases. Allen (1937) injected 250-gram guinea
pigs with 4 milligrams of venom of various poisonous snakes. Survival
time was recorded in order to indicate the relative potency of the
venoms. Of 16 such tests _C. adamanteus_ held places 1, 2, 3, 12, and
16; _Bothrops atrox_ held places 4, 9, 10, and 13; and _A. piscivorus_
held places 5, 7, 8, and 15. Places 6, 11, and 14 were held by three
individuals of different species. No relationship to size or sex was
indicated by the results of this experiment.
Susceptibility of Snakes
Numerous experiments have been conducted to determine the susceptibility
of various snakes to venom. The majority of these experiments were
performed to learn whether or not venomous snakes were immune to their
own poison. Conant (1934:382) reported on a 30-inch cottonmouth that
killed two Pacific rattlesnakes and another cottonmouth. One rattlesnake
was bitten on the tail and the other on or near the head and partially
swallowed. Gloyd (1933:13-14) recorded fatal effects to a rattlesnake
from the bite of a cottonmouth. He also reported on the observations of
three other crotalids bitten by themselves or other snakes, from which
no harmful effects were observed. Allen (1937) injected several snakes
with dried cottonmouth venom which was diluted with distilled water just
before each injection. Four cottonmouths receiving 9, 18, 19, and 20
milligrams of venom per ounce of body weight survived, while another
receiving 18.7 milligrams per ounce died after three hours. A specimen
of _S. miliarius_ receiving 8.3 milligrams per ounce died in about ten
hours, while a _C. durissus_ receiving 12.5 milligrams per ounce
succumbed in 45 minutes. An alligator receiving 6 milligrams per ounce
died in 14 hours. Even the snakes that survived showed some degree of
swelling.
The studies of Keegan and Andrews (1942:252) show that king-snakes are
sometimes killed by poisonous snakes. A _Lampropeltis calligaster_
injected with _A. contortrix_ venom (0.767 milligrams per gram) died
five days following the injection. This amount was more than twice the
amount of _A. piscivorus_ venom injected into a _L. getulus_ by Allen
(1937) in which the snake showed no ill effects. Keegan and Andrews
(_loc. cit._) stated that success in overpowering and eating poisonous
snakes by _Lampropeltis_ and _Drymarchon_ may be due to the ability to
avoid bites rather than to immunity to the venom. However, Rosenfeld and
Glass (1940) demonstrated that the plasma of _L. g. getulus_ had an
inhibiting effect on the hemorrhagic action on mice of the venoms of
several vipers.
One of the more extensive studies on effects of venoms on snakes is that
by Swanson (1946:242-249). In his studies freshly extracted liquid venom
was used. His studies indicated that snakes are not immune to venom of
their own kind or to closely related species. Copperhead venom killed
copperheads faster than did other venoms but took more time to kill
massasaugas, cottonmouths, and timber rattlers. However, most of the
snakes were able to survive normal or average doses of venom although
they are not necessarily immune to it.
One of the major problems in comparing the data on toxicity of venom in
studies of this type is that no standard method of estimating toxicity
has been used. Swanson's (_loc. cit._) amount of venom equalling one
minim (M.L.D.?) ranged from 0.058 to 0.065 cubic centimeters. There were
no different values given for each species, but the time that elapsed
from injection of the venom to death represented the toxicity. There
also was no attempt in his study to convert the amount of venom used
into a ratio of the volume of venom per weight of snake, making the
results somewhat difficult to interpret. Additional work in this field
should provide for many injections into many individuals of several size
classes. The studies to date have been on far too few individuals to
allow statistical analyses to be accurate.
THE BITE
Effects of the Bite
Factors determining the outcome of snakebite are: size, health, and
species of snake; individual variation of venom toxicity of the species;
age and size of the victim; allergic or immune responses; location of
the bite; and the amount of venom injected and the depth to which it is
injected. The last factor is one of the most variable, owing to (1)
character and thickness of clothing between the snake and the victim's
skin, (2) accuracy of the snake's strike, and (3) size of the snake,
since a large snake can deliver more venom and at a greater depth than
can a small snake.
Pope and Perkins (1944) demonstrated that pit-vipers of the United
States bite as effectively as most innocuous snakes and that a careful
study of the bite may reveal the location of the pocket of venom, size
of the snake, and possibly its generic identity (see Dentition). The
bite pattern of the cottonmouth as well as the other crotalids showed
the typical fang punctures plus punctures of teeth on both the pterygoid
and mandible. Even so, a varying picture may be presented because from
one to four fang marks may be present. At times in the fang-shedding
cycle three and even four fangs can be in operation simultaneously.
Various authors have attributed death of the prey to the following
causes: paralysis of the central nervous system, paralysis of the
respiratory center, asphyxiation from clotting of the blood, stoppage of
the heart, urine suppression due to crystallized hemoglobin in the
kidney tubules, dehydration of the body following edema in the area of
the bite, or tissue damage. Mouths of snakes are reservoirs for
infectious bacteria, which are especially prolific in damaged tissue.
Bacterial growth is aided by the venom which blocks the bactericidal
power of the blood.
Three grades in the severity of snakebite (I, minimal; II, moderate; and
III, severe) were described by Wood, Hoback, and Green (1955). Parrish
(1959:396) added a zero classification to describe the bite of a
poisonous snake in which no envenomation occurred. Grade IV (very
severe) was added by McCollough and Gennaro (1963:961) to account for
many bites of the eastern and western diamondback rattlesnakes.
The first symptom of poisonous snakebite is an immediate burning
sensation at the site of the bite. Within a few minutes the loss of
blood into the tissues causes discoloration. Swelling proceeds rapidly
and can become so great as to rupture the skin. Pain is soon felt in the
lymph ducts and glands. Weakness, nausea, and vomiting may ensue at a
relatively early stage. Loss of blood into tissues may spread to the
internal organs. In conjunction with a rapid pulse, the blood pressure
and body temperature can drop. Some difficulty in breathing can occur,
especially if large amounts of neurotoxin are present in the venom. In
severe cases the tension due to edema obstructs venous and even arterial
flow, in which case bacteria may multiply rapidly in the necrotic tissue
and gangrene can occur. Blindness due to retinal hemorrhages may occur.
Symptoms of shock may be present after any bite.
Treatment
Perhaps one of the most important factors in the outcome of snakebite is
the treatment. Because of the variable reactions to snakebite, treatment
should vary accordingly. Many methods have been proposed for treating
snakebite, and there is disagreement as to which is the best. The list
of remedies that have been used in cases of snakebite includes many that
add additional injury or that possibly increase the action of the venom.
The use of poultices made by splitting open living chickens and the use
of alcohol, potassium permanganate, strychnine, caffeine, or injection
of ammonia have no known therapeutic value, and may cause serious
complications. The most important steps in the treatment of snakebite
are to prevent the spread of lethal doses of venom, to remove as much
venom as possible, and to neutralize the venom as quickly as possible.
It is generally agreed that the first step in snakebite treatment should
be to place a ligature above the bite to restrict the flow of venom, and
also to immobilize the patient as much as possible. The ligature should
be loosened at least every fifteen minutes. The next steps are
sterilization of the skin and the making of an incision through the fang
punctures. As pointed out by Stahnke (1954:8), the incision should be
made in line with the snake's body at the time of the bite, so as to
account for the rearward curvature of the fangs and possibly to reach
the deposition of venom. Many instruction booklets and first-aid guides
have specified the length and depth of incision to be made, but the
actual size and depth of the cut should depend upon the location of the
bite. An "X" cut or connection of the fang punctures is likely to
facilitate the spread of the venom. No cut should be made that would
sever a large blood vessel or ligament.
Extensive damage is often caused by well-meaning individuals whose
attempts at first aid result in brutally deep incisions and tourniquets
applied too tightly and for too long a period of time; the resultant
damage in many instances exceeds that of the bite itself (Stimson and
Engelhardt, 1960:165). Stimson and Engelhardt also think that time
should be sacrificed to surgical cleanliness, and incisions should not
be made if a hospital can be reached within an hour.
The ligature-cryotherapy (L-C) method proposed by Stahnke (1953) has
been severely criticized by other workers. He stated that the ligature
should be tight enough to restrict completely the flow of venom until
the temperature of the area can be lowered sufficiently to prevent any
action of the venom. After 10 minutes the ligature may be removed and
the bitten area kept immersed in a vessel of crushed ice and water. If
the envenomized member is to be treated for more than four hours (which
is the case with almost all pit-viper bites), it should be protected by
placing it in a plastic bag. The venom action should be tested after 12
or more hours. This consists of a brief warming period to determine
whether or not the action of the venom can be felt. The patient should
be kept warm at all times; and the warming at the termination of
treatment should be done gradually, preferably by allowing the water to
warm slowly to room temperature.
Advocates of the L-C method warn against making incisions unless they
are absolutely necessary, the theory being that each cut permits
additional bacterial infection and does little good in removing venom.
However, McCollough and Gennaro (1963:963) demonstrated that, in bites
where the fangs had only slightly penetrated the skin, more than 50 per
cent of the venom was removed in some instances if suction was started
within three minutes after the injection. With deeper injection the
amount of venom recovered sometimes reached 20 per cent of the dose.
Stahnke suggested that an incision be made at the site of the bite only
after the site has been refrigerated for at least 30 minutes.
Stimson and Engelhardt (_loc. cit._) stated that two constricting bands
should be used between the bite and the body and that cracked ice in a
cloth should be applied to the bite before reaching a hospital. In
addition, they suggested the following procedure. Rings of incisions
should follow the swelling, and suction should continue for several
hours. After the edema has receded, the limb should be wrapped in a
towel containing crushed ice. Antivenin should be given only in severe
cases. Calcium gluconate and gas gangrene antitoxin as well as
antibiotics are helpful.
The most recent and up-to-date summary of snakebite treatment is that by
McCollough and Gennaro (1963). Following is a brief summary of their
suggestions:
1. Immobilization--Systemic immobilization is effected by body
rest and locally by splinting the bitten area.
2. Tourniquet--A lightly occlusive tourniquet during a 30- to
60-minute period of incision and suction would seem to possess
some advantages. In severe cases where medical attention is
hours away, a completely occlusive tourniquet may be necessary
to prevent death. Sacrifice of the extremity may be necessary
for the preservation of life.
3. Incision and suction--Suction should begin three to five
minutes after injection of venom if symptoms of poisoning are
present. Incisions one-fourth inch to an inch long across each
fang mark should be made in order to open the wound for more
efficient suction. Multiple incisions are not useful for the
removal of venom but may be employed under hospital conditions
to reduce subcutaneous tensions and ischemia.
4. Cryotherapy--An ice cap over the site of the bite for relief
of pain would seem to be permissible, especially prior to the
administration of antivenin. It must be remembered that cooling
during the administration of the antivenin radically reduces
the access of the antiserum to the bite area.
5. Antivenin--Antiserum is the keystone to the therapy of
snakebite. Careful evaluation of the severity of the bite and
the patient's sensitivity should be made before the use of
antivenin. In Grade II (moderate) bites, the intramuscular
injection on the side of the bite may suffice. In Grades III
(severe) and IV (very severe), shock and systemic effects
require intravenous injection. In bites producing symptoms of
this severity, antivenin must be given in amounts large enough
to produce clinical improvement. Ten to 20 units may be
necessary to prevent the relapse that sometimes occurs after
small doses of antivenin. Permanent remission of swelling and
interruption of necrosis are the therapeutic end point in the
clinical use of the antiserum.
In all cases of snakebite where there is any doubt as to the snake's
identity, it should be killed if possible and taken to the hospital for
positive identification. In many instances of actual bites by poisonous
snakes the only treatment needed was an injection of tetanus antitoxin
or toxoid and sedation, because physical examination revealed no
indication of poisoning (Stimson and Engelhardt, _loc. cit._).
Case History of a Bite
On July 29, 1963, at 8:20 a.m., I was treating a nine-month-old
cottonmouth for mites. As I dropped the snake into a sink, it twisted
its head and bit the tip of my right middle finger with one fang. The
fang entered just under the fingernail and was directed downward, the
venom being injected about five millimeters below the site of fang
penetration. After placing the snake back in its cage, I squeezed the
finger once to promote bleeding, wrapped a string around the base of the
finger, and drove to Watkins Memorial Hospital on the University of
Kansas campus. I began to feel a burning sensation in the tip of the
finger almost immediately. Upon my arrival at the hospital, an
additional ligature was placed around my wrist. At 8:30 a.m. a small
incision was made in the end of the finger, which by this time was
beginning to darken at the point of venom deposition. I sucked on the
finger until 8:35 a.m., when a pan of ice water that I had requested was
brought to me. No pain was felt except that caused by the ice. Fresh ice
was added as needed to keep the temperature low. By 9:30 a.m. the
finger had swollen and stiffened. At 10:00 a.m. the swelling had
progressed to the index finger and back of the hand. I experienced
difficulty in opening and closing the hand. Blood oozed slowly from the
incision. A dull ache persisted and about every two to four minutes a
sharp throb could be felt until nearly 11:00 a.m., when the pain
diminished. The rate and intensity of throbbing increased whenever the
hand was removed from the ice bath for more than a few seconds. Although
only the hand was immersed, the entire forearm was cold. Pain was felt
along the lymphatics on top of the arm when it was touched, and by 1:00
p.m. a slight pain could be felt in the armpit. Since swelling and pain
were almost nonexistent by 2:00 p.m., I was permitted to leave. After
walking to a nearby building, I again felt a burning sensation as the
hand warmed. I made another ice bath and again immersed the hand in it
until 4:10 p.m., at which time it was removed from the water. The pain
and swelling began anew, and the hand was placed back in an ice bath
from 5:30 p.m. until about 7:30 p.m. At this time cryotherapy was
discontinued. From 10:00 p.m. to 12:00 midnight my legs twitched
periodically, and pain could be felt in both armpits. A slight
difficulty in breathing also was experienced for a short time. The acute
pain and burning sensation remained in the finger until the following
morning, but swelling progressed only as far as the wrist. The only
discomfort that day was in the finger. The tip was darkened, the entire
first digit red and feverish, and the lymphatics still painful when
touched. By the third day the swelling had regressed. The incision
itself was the main cause of discomfort, and the soreness at the site of
the bite persisted for at least four days.
Although the L-C method of snakebite treatment has been vigorously
attacked by many, there is still need of much more data before it
can be unequivocally condemned or praised. It was preferred in the
treatment of this bite because: I knew that envenomation was minimal
and that there would be no need for antivenin; only one fang of a
snake less than one foot long had entered the tip of the finger; the
snake had bitten three frogs in the previous two days and had
possibly used up a considerable amount of its venom; the venom was
deposited at such a shallow depth that at least a portion of it
could be removed by suction; and the wound bled freely even before
suction was applied. The ice water was uncomfortably cold but was
not cold enough to cause frostbite, a major objection to the L-C
method. Ideally, fresh ice should be added little by little to
replace that which is melting, and the immersed area should be
protected from the water by a plastic bag. Pain and swelling can be
minimized by cryotherapy, but I would recommend its use only in
cases of mild poisoning such as the one described herein.
Snakebite in the United States
Many estimates have been made of the number of bites of poisonous snakes
that occur annually in the United States. The occurrence of poisonous
snakebite has been nearly as badly underestimated as fatal results of
their envenomations have been overrated. For important data on number of
persons bitten by poisonous snakes in the United States, see the
following: Allen and Swindell (1948:15); Githens (1935:172); Klauber
(1956:811); Parrish (1963); Sowder and Gehres (1963:973); Stimson and
Engelhardt (1960:153); Swaroop and Grab (1956:441); Swartzwelder
(1950:579); Willson (1908:530); and Wood (1954b:937).
Judging from estimates made in several states, the number of poisonous
snakebites in the United States would be about 5000 per year. In the
region where the cottonmouth occurs there are approximately 2000 persons
bitten annually by poisonous snakes. Of these approximately 39 per cent
are copperhead bites, 30 per cent each are cottonmouth and rattlesnake
bites, and I per cent are coral snake bites. These percentages vary
considerably from place to place, because of the distribution and
abundance of the eight species of poisonous snakes whose ranges overlap
that of the cottonmouth.
According to Parrish (1963), about 14 people die of snakebite each year
in the United States. Of these deaths, about 6.6 per cent are
attributable to cottonmouths, 77.0 per cent to rattlesnakes, and 1.6 per
cent to coral snakes; 14.8 per cent are unidentified. Almost half of the
fatalities are in persons less than 20 years of age, the high mortality
rate being partially due to the greater ratio of venom to body weight.
SUMMARY
In my study, 306 living and preserved cottonmouths were examined. This
species occurs throughout the coastal plains of the southeastern United
States, usually at altitudes of less than 500 feet but occasionally up
to altitudes of more than 2000 feet.
Two subspecies are recognized: the eastern cottonmouth, _A. p.
piscivorus_, occurring from extreme eastern Mississippi to southeastern
Virginia and Florida; and the western cottonmouth, _A. p. leucostoma_,
occurring from eastern Mississippi northward to southern Illinois and
Missouri and westward to central Texas. Intergradation occurs in eastern
Mississippi.
The northern edge of the range is probably limited by low temperatures
in winter, and the western edge by lack of available habitat resulting
from insufficient precipitation. Old records of occurrence indicate that
the range has decreased in the last 100 years. The species inhabits
mostly areas where water is found, but at times wanders a mile or more
from the nearest water.
The ground color is predominantly a brown, but varies from a
brownish-green to almost black with a pattern of 10 to 17 irregular
bands of a darker shade of brown. The pattern is better defined in the
eastern subspecies than in the western.
The scutellation resembles that of other species of _Agkistrodon_. In
the specimens examined supralabials ranged from 7 to 9, and infralabials
from 8 to 12. The number of dorsal scale rows on the neck, at mid-body,
and immediately anterior to the anus is relatively constant at 27-25-21,
respectively. Ventral scales of 34 males averaged 134.4 (128 to 139),
and those of 48 females 133.5 (128 to 137). The number of caudal scales
showed some degree of sexual dimorphism; the average was 45.4 (41 to 50)
in 34 males and 42.6 (39 to 49) in 44 females. In general, caudal scales
on the basal half of the tail are undivided, whereas those on the distal
half are divided. No marked geographical variation was found in any
scale character.
The poison fangs vary in length from 1.3 per cent of snout-vent length
in juveniles to 1.0 per cent in large adults. Fangs of captive
cottonmouths were shed and replaced at intervals of about 21 days, but
the interval was variable. Relationships in distance between the base of
fangs and between fang punctures in an actual bite indicate that
examination of the wound does not provide a good basis for judging
accurately the size of the snake that inflicted the bite.
In general, females less than 450 millimeters in snout-vent length were
juveniles; those more than 450 millimeters were classified as post
partum or reproductive on the basis of sizes of ovarian follicles. Since
about half the adult females were fecund, it was concluded that a
biennial reproductive cycle occurs in this species. An annual cycle may
occur in areas where temperature permits year-round activity. It was
estimated that females become sexually mature at an age of approximately
two and one-half years. Mating is probably most concentrated in early
spring at about the time when females ovulate, but copulation is not a
stimulus for ovulation. Sperm retention and delayed fertilization allow
young to be produced without copulation occurring in each breeding
season. The testes increase in size gradually rather than rapidly at
maturity or in each breeding season, but seasonal cycles in sperm
production occur.
The gestation period is three and one-half to four months. Determination
of sex in the embryos is possible by late June, because the hemipenes of
males are evaginated until the time of birth. Parturition generally
occurs in August or September, but captivity may delay birth for a month
or more. From one to 16 young per litter are born, depending on size of
the mother and other factors; but the average is between six and seven.
Mortality rate at birth is high in captive individuals but has not been
determined in natural populations. The sex ratio in embryos and adults
examined revealed about 53 per cent females. Because sufficient
information on population composition is not available, an estimate of
the percentage of adults in a natural population was based upon the
number found in my study. The reproductive potential was estimated from
these figures.
Normal young at birth are 230 to 240 millimeters in snout-vent length,
but their size is influenced by the condition of the mother. Comparison
of newborn young with those captured in spring indicates that little
growth occurs during winter. Early growth is largely dependent upon
feeding before winter quiescence.
The umbilical cord is broken at birth and the navel closes within a few
days, but the scar remains throughout life. Sexual dimorphism in the
position of the scar is characteristic of some snakes but is minimal in
cottonmouths.
In those snakes more than 700 millimeters in length, males outnumber
females three to one. The maximum age of cottonmouths in nature is
unknown, but one has been kept in captivity for more than 18 years.
Allometric growth is striking in cottonmouths. The head and tail are
proportionately longer in young individuals than in adults; and in males
the tail is, on the average, slightly longer than in females of the same
size.
Shedding of the skin provides for growth and wear in snakes. The young
shed within a few days after birth and generally shed more frequently
than adults. Frequency of shedding depends mostly on amount of food
consumed, and there is some evidence that injuries on the head and neck
increase the frequency of shedding. Before shedding, the eyes become
cloudy for about five and one-half days, then clear up again for about
four days before the skin is shed.
The food of cottonmouths consists mainly of small vertebrates and
occasionally invertebrates that are found near water. Fish, amphibians,
and reptiles make up nearly 70 per cent of the diet. Carrion is also
eaten and cannibalism occurs occasionally. Food is obtained by lying in
ambush or by active searching. The young are known to lure their prey
within striking range by waving their yellow tails in a manner
suggestive of writhing grubs. The method of obtaining prey differs
according to the kind of prey. Generally, cottonmouths retain their hold
on fish or frogs but release mice and larger prey after delivering a
bite.
The major causes of mortality of cottonmouths are obscure. Predators are
known to include alligators, indigo snakes, king-snakes, largemouth
bass, and blue herons; there are probably numerous others. Heavy
parasitic infestations were found among the snakes examined. Snake
mites, _Ophionyssus natricus_, became increasingly abundant on almost
all captive snakes in April and May of 1963. Lung flukes (_Ochetosoma_
sp.) were in 16 of 20 captive snakes, and many preserved specimens
contained nematodes (_Kalicephalus_ sp.) in the stomach and/or tapeworms
(_Ophiotaenia_ sp.) in the intestine. Although parasitic infestation
causes discomfort and may lower resistance to other detrimental factors,
it is difficult to attribute death to the effect of any particular kind
of parasite. Miscellaneous causes of death of some captive snakes also
were discussed.
The maximal body temperatures tolerated by four cottonmouths were
between 38° and 40° C., but a temperature of 38° was lethal to a fifth
individual. Cottonmouths have been found on occasion when other snakes
were inactive because of low temperatures, but minimal temperatures
tolerated by this species are not known. The annual cycle of activity is
dependent upon temperature and thus varies from north to south.
Cottonmouths generally migrate inland in autumn, usually to dry forested
hillsides, where they den along with other species of snakes. After a
few warm days in spring they migrate back to the water's edge. The diel
activity cycle likewise depends upon temperatures but is influenced by
other factors as well. In spring and autumn, the snakes are active
mostly on warm, sunny days, whereas in summer they are active mostly at
night. In order to maintain adequate internal temperatures, much time is
spent basking mostly in a characteristic flat, resting coil either
beside a body of water or above water on limbs of dead trees. In this
position the snake is ready either for a short strike or a hasty
getaway.
Juveniles appear particularly aggressive and strike repeatedly when
approached, a behavioral pattern definitely favoring survival. Adults
vary in disposition, usually appearing sluggish and lazy, but they are
capable of striking rapidly when disturbed. The typical threat display
consists of lying in a coiled position with the mouth opened widely,
exposing the white interior, and with the tail vibrating rapidly. The
striking posture resembles the resting coil except that the anterior
part of the body is raised off the ground and the mouth is sometimes
opened. Musk is often ejected in a fine spray from glands in the tail as
a further defensive action.
"Head bobbing," more properly described as spastic contractions of the
body, was observed in captives when food was introduced into a cage
containing several individuals or when one of the snakes was returned to
the cage after being handled. Reports in the literature also have
connected these jerking movements with courtship. The response appears
to be elicited whenever a nervous state is recognized in another
individual and may serve to protect the jerking individual from
aggressive advances of the former.
The relatively heavy appearance of the body, sluggish habits, and
cryptic coloration are correlated with the development of venom and
fangs. The poison apparatus has developed primarily as a means of
causing rapid death in prey and secondarily, perhaps, to begin the
digestion of small animals that are the usual prey, but it is also
important as a defensive device. The venom contains at least eight
constituents that aid in its action on prey. Toxicity of the venom is
difficult to determine because of numerous variables, but cottonmouth
venom is generally believed to be less potent than that of most
rattlesnakes and more potent than that of the copperhead. Snakes in
general are more resistant to snake venoms than other vertebrates of
similar size, but there is no immunity even to their own venom.
About ten per cent of the approximately 5000 bites of poisonous snakes
per year in the United States are attributable to cottonmouths, and
about seven per cent of the approximately 14 deaths per year are caused
by cottonmouths.
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1954. Polyvalent antivenin in the treatment of experimental snake
venom poisoning. Amer. Jour. Trop. Med. and Hyg., 3:1077-1082.
1956. Some properties of North American pit viper venoms and their
correlation with phylogeny. Pp. 145-151 _in_ Venoms (ed. Buckley,
E. E., and Porges, N., Amer. Assoc. Adv. Sci., Publ. No. 44).
MUNRO, D. F.
1949. Effect of DDT powder on small cottonmouths. Herpetologica,
5:71-72.
1950. Additional observations on head bobbing by snakes.
Herpetologica, 6:88.
NEILL, W. T.
1947. Size and habits of the cottonmouth moccasin. Herpetologica,
3:203-205.
1949. Head bobbing, a widespread habit of snakes. Herpetologica,
5:114-115.
1960. The caudal lure of various juvenile snakes. Quart. Jour.
Florida Acad. Sci., 23(3):173-200, 2 figs.
NEILL, W. T., and ALLEN, E. R.
1955. Metachrosis in snakes. Quart. Jour. Florida Acad. Sci.,
18(3):207-215.
NETTING, M. G.
1929. The venom of _Sistrurus catenatus_. Bull. Antivenin Inst.
Amer., 2(4):108-109.
PARRISH, H. M.
1959. Poisonous snakebites resulting in lack of venom poisoning.
Virginia Med. Month, 86:396-401.
1963. Analysis of 460 fatalities from venomous animals in the
United States. Amer. Jour. Med. Sci., 245(2):35-47.
PARRISH, H. M., and POLLARD, C. B.
1959. Effects of repeated poisonous snakebite in man. Amer. Jour.
Med. Sci., 237(3):277-286.
PENN, G. H.
1943. Herpetological notes from Cameron Parish, Louisiana. Copeia,
1943(1):58-59.
PERKINS, C. B.
1955. Longevity of snakes in captivity in the United States.
Copeia, 1955(3):262.
POPE, C. H., and PERKINS, R. M.
1944. Differences in the patterns of bites of venomous and of
harmless snakes. Archives of Surgery, 49:331-336.
RAHN, H.
1942. The reproductive cycle of the prairie rattler. Copeia,
1942(4):233-240.
RAMSEY, L. W.
1948. Combat dance and range extension of _Agkistrodon
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RICHMOND, M. D.
1952. Head bobbing in reptiles. Herpetologica, 8:38.
ROSENFELD, S., and GLASS, S.
1940. The inhibiting effect of snake bloods upon the hemorrhagic
action of viper venoms on mice. Amer. Jour. Med. Sci.,
199:482-486.
SCHMIDT, K. P.
1946. On the zoogeography of the Holarctic region. Copeia,
1946:144-152.
SHAW, C. E.
1948. The male combat "dance" of some crotalid snakes.
Herpetologica, 4:137-145.
1951. Male combat in American colubrid snakes with remarks on
combat in other colubrid and elapid snakes. Herpetologica,
7(4):149-168.
SMITH, H. M.
1956. Handbook of amphibians and reptiles of Kansas. 2nd
Edition. Univ. Kansas Mus. Nat. Hist., Misc. Publ., 9:1-356, 253
figs.
SMITH, H. M., and BUECHNER, H. K.
1947. The influence of the Balcones Escarpment on the
distribution of amphibians and reptiles in Texas. Bull. Chicago
Acad. Sci., pp. 1-16.
SMITH, P. W.
1961. The amphibians and reptiles of Illinois. Illinois Nat.
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SMITH, P. W., and LIST, J. C.
1955. Notes on Mississippi amphibians and reptiles. Amer. Midl.
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SOWDER, W. T., and GEHRES, G. W.
1963. Snakebites in Florida. Jour. Florida Med. Assn.,
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STABLER, R. M.
1951. Some observations on two cottonmouth moccasins made during
12 and 14 years of captivity. Herpetologica, 7:89-92.
STAHNKE, H. M.
1953. The L-C treatment of venomous bites and stings. Amer. Jour.
Trop. Med. and Hyg., 2(1):142-143.
1954. The L-C method of treating venomous bites and stings. Pois.
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1960. The treatment of snakebite. Jour. Occ. Med., 2(4):163-168.
SUTHERLAND, I. D.
1958. The "combat dance" of the timber rattlesnake. Herpetologica,
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1946. Effects of snake venoms on snakes. Copeia, 1946(4):242-249.
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1950. Snake-bite accidents in Louisiana with data on 306 cases.
Amer. Jour. Trop. Med., 30(4):575-589.
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1962. Reproductive potential and cycles in female _Crotalus atrox_
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1937. Ecological observations on amphibians and reptiles collected
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1939a. Record venom extraction from water moccasin. Copeia,
1939(1):52.
1939b. Yield and toxicity of venom from snakes extracted over a
period of two years. Copeia, 1939(4):234.
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1954a. The distribution of poisonous snakes in Virginia. Virginia
Jour. Sci., 5(3):152-167, 4 maps.
1954b. A survey of 200 cases of snake-bite in Virginia. Amer. Jour.
Trop. Med. and Hyg., 3(5):936-943.
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1958. Systema helminthum. Interscience Publ., Inc., New York, 3
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YERGER, R. W.
1953. Yellow bullhead preyed upon by cottonmouth moccasin. Copeia,
1953(2):115.
_Transmitted June 20, 1966._
UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY
Institutional libraries interested in publications exchange may obtain
this series by addressing the Exchange Librarian, University of Kansas
Library, Lawrence, Kansas. Copies for individuals, persons working in a
particular field of study, may be obtained by addressing instead the
Museum of Natural History, University of Kansas, Lawrence, Kansas. When
copies are requested from the Museum, 25 cents should be included (for
each 100 pages or part thereof) for the purpose of defraying the costs
of wrapping and mailing. For certain longer papers an additional amount
indicated below, toward the cost of production, is to be included.
Materials published to date in this series are as follows.
* An asterisk designates those numbers of which the Museum's
supply (not necessarily the Library's supply) is exhausted.
Materials published to date, in this series, are as follows:
Vol. 1.
Nos. 1-26 and index. Pp. 1-638, 1946-1950.
*Vol. 2.
(Complete) Mammals of Washington. By Walter W. Dalquest. Pp.
1-444, 140 figures in text. April 9, 1948.
*Vol. 3.
Nos. 1-4 and index. Pp. 1-681. 1951.
*Vol. 4.
(Complete) American weasels. By E. Raymond Hall. Pp. 1-466, 41
plates, 31 figures in text. December 27, 1951.
Vol. 5.
Nos. 1-37 and index. Pp. 1-676, 1951-1953.
*Vol. 6.
(Complete) Mammals of Utah, _taxonomy and distribution_. By
Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables.
August 10, 1952.
Vol. 7.
Nos. 1-15 and index. Pp. 1-651, 1952-1955.
Vol. 8.
Nos. 1-10 and index. Pp. 1-675, 1954-1956.
Vol. 9.
Nos. 1-23 and index. Pp. 1-690, 1955-1960.
Vol. 10.
Nos. 1-10 and index. Pp. 1-626, 1956-1960.
Vol. 11.
Nos. 1-10 and index. Pp. 1-703, 1958-1960.
Vol. 12.
*1. Functional morphology of three bats: Eumops, Myotis,
Macrotus. By Terry A. Vaughan. Pp. 1-153, 4 plates, 24 figures
in text. July 8, 1959.
*2. The ancestry of modern Amphibia: a review of the evidence.
By Theodore H. Eaton, Jr. Pp. 155-180, 10 figures in text. July
10, 1959.
3. The baculum in microtine rodents. By Sydney Anderson. Pp.
181-216, 49 figures in text. February 19, 1960.
*4. A new order of fishlike Amphibia from the Pennsylvanian of
Kansas. By Theodore H. Eaton, Jr., and Peggy Lou Stewart. Pp.
217-240, 12 figures in text. May 2, 1960.
5. Natural history of the Bell Vireo. By Jon C. Barlow. Pp.
241-296, 6 figures in text. March 7, 1962.
6. Two new pelycosaurs from the lower Permian of Oklahoma. By
Richard C. Fox. Pp. 297-307, 6 figures in text. May 21, 1962.
7. Vertebrates from the barrier island of Tamaulipas, México.
By Robert K. Selander, Richard F. Johnston, B. J. Wilks, and
Gerald G. Raun. Pp. 309-345, plates 5-8. June 18, 1962.
8. Teeth of edestid sharks. By Theodore H. Eaton, Jr. Pp.
347-362, 10 figures in text. October 1, 1962.
9. Variation in the muscles and nerves of the leg in two genera
of grouse (Tympanuchus and Pedioecetes). By E. Bruce Holmes.
Pp. 363-474, 20 figures. October 25, 1962. $1.00.
10. A new genus of Pennsylvanian fish (Crossopterygii,
Coelacanthiformes) from Kansas. By Joan Echols. Pp. 475-501, 7
figures. October 25, 1963.
11. Observations on the Mississippi Kite in southwestern
Kansas. By Henry S. Fitch. Pp. 503-519. October 25, 1963.
12. Jaw musculature of the Mourning and White-winged doves. By
Robert L. Merz. Pp. 521-551, 22 figures. October 25, 1963.
13. Thoracic and coracoid arteries in two families of birds,
Columbidae and Hirundinidae. By Marion Anne Jenkinson. Pp.
553-573, 7 figures. March 2, 1964.
14. The breeding birds of Kansas. By Richard F. Johnston. Pp.
575-655, 10 figures. May 18, 1964. 75 cents.
15. The adductor muscles of the jaw in some primitive reptiles.
By Richard C. Fox. Pp. 657-680, 11 figures in text. May 18,
1964.
Index. Pp. 681-694.
Vol. 13.
1. Five natural hybrid combinations in minnows (Cyprinidae). By
Frank B. Cross and W. L. Minckley. Pp. 1-18. June 1, 1960.
2. A distributional study of the amphibians of the Isthmus of
Tehuantepec, México. By William E. Duellman. Pp. 19-72, plates
1-8, 3 figures in text. August 16, 1960. 50 cents.
3. A new subspecies of the slider turtle (Pseudemys scripta)
from Coahuila, México. By John M. Legler. Pp. 73-84, plates
9-12, 3 figures in text. August 16, 1960.
*4. Autecology of the copperhead. By Henry S. Fitch. Pp.
85-288, plates 13-20, 26 figures in text. November 30, 1960.
5. Occurrence of the garter snake, Thamnophis sirtalis, in the
Great Plains and Rocky Mountains. By Henry S. Fitch and T. Paul
Maslin. Pp. 289-308, 4 figures in text. February 10, 1961.
6. Fishes of the Wakarusa River in Kansas. By James E. Deacon
and Artie L. Metcalf. Pp. 309-322, 1 figure in text. February
10, 1961.
7. Geographic variation in the North American cyprinid fish,
Hybopsis gracilis. By Leonard J. Olund and Frank B. Cross. Pp.
323-348, plates 21-24, 2 figures in text. February 10, 1961.
8. Descriptions of two species of frogs, genus Ptychohyla;
studies of American hylid frogs, V. By William E. Duellman. Pp.
349-357, plate 25, 2 figures in text. April 27, 1961.
9. Fish populations, following a drought, in the Neosho and
Marais des Cygnes rivers of Kansas. By James Everett Deacon.
Pp. 359-427, plates 26-30, 3 figures. August 11, 1961. 75
cents.
10. Recent soft-shelled turtles of North America (family
Trionychidae). By Robert G. Webb. Pp. 429-611, plates 31-54, 24
figures in text. February 16, 1962. $2.00.
Index. Pp. 613-624.
Vol. 14.
1. Neotropical bats from western México. By Sydney Anderson.
Pp. 1-8. October 24, 1960.
2. Geographic variation in the harvest mouse, Reithrodontomys
megalotis, on the central Great Plains and in adjacent regions.
By J. Knox Jones, Jr., and B. Mursaloglu. Pp. 9-27, 1 figure in
text. July 24, 1961.
3. Mammals of Mesa Verde National Pork, Colorado. By Sydney
Anderson. Pp. 29-67, plates 1 and 2, 3 figures in text. July
24, 1961.
4. A new subspecies of the black myotis (bat) from eastern
Mexico. By E. Raymond Hall and Ticul Alvarez. Pp. 69-72, 1
figure in text. December 29, 1961.
5. North American yellow bats, "Dasypterus," and a list of the
named kinds of the genus Lasiurus Gray. By E. Raymond Hall and
J. Knox Jones, Jr. Pp. 73-98, 4 figures in text. December 29,
1961.
6. Natural history of the brush mouse (Peromyscus boylii) in
Kansas with description of a new subspecies. By Charles A.
Long. Pp. 99-111, 1 figure in text. December 29, 1961.
7. Taxonomic status of some mice of the Peromyscus boylii group
in eastern Mexico, with description of a new subspecies. By
Ticul Alvarez. Pp. 113-120, 1 figure in text. December 29,
1961.
8. A new subspecies of ground squirrel (Spermophilus spilosoma)
from Tamaulipas, Mexico. By Ticul Alvarez. Pp. 121-124. March
7, 1962.
9. Taxonomic status of the free-tailed bat, Tadarida yucatanica
Miller. By J. Knox Jones, Jr., and Ticul Alvarez. Pp. 125-133,
1 figure in text. March 7, 1962.
10. A new doglike carnivore, genus Cynaretus, from the
Clarendonian Pliocene, of Texas. By E. Raymond Hall and Walter
W. Dalquest. Pp. 135-138, 2 figures in text. April 30, 1962.
11. A new subspecies of wood rat (Neotoma) from northeastern
Mexico. By Ticul Alvarez. Pp. 139-143, April 30, 1962.
12. Noteworthy mammals from Sinaloa, Mexico. By J. Knox Jones,
Jr., Ticul Alvarez, and M. Raymond Lee. Pp. 145-159. 1 figure
in text. May 18, 1962.
13. A new bat (Myotis) from Mexico. By E. Raymond Hall. Pp.
161-164, 1 figure in text. May 21, 1962.
*14. The mammals of Veracruz. By E. Raymond Hall and Walter W.
Dalquest. Pp. 165-362, 2 figures. May 20, 1963. $2.00.
15. The recent mammals of Tamaulipas, México. By Ticul Alvarez.
Pp. 363-473, 5 figures in text. May 20, 1963. $1.00.
16. A new subspecies of the fruit-eating bat, Sturnira
ludovici, from western Mexico. By J. Knox Jones, Jr., and Gary
L. Phillips. Pp. 475-481, 1 figure in text. March 2, 1964.
17. Records of the fossil mammal Sinclairella, Family
Apatemyidae, from the Chadronian and Orellan. By William A.
Clemens. Pp. 483-491. 2 figures in text. March 2, 1964.
18. The mammals of Wyoming. By Charles A. Long. Pp. 493-758, 82
figs. July 6, 1965. $3.00.
Index. Pp. 759-784.
Vol. 15.
1. The amphibians and reptiles of Michoacán, México. By William
E. Duellman. Pp. 1-148, plates 1-6, 11 figures in text.
December 20, 1961. $1.50.
2. Some reptiles and amphibians from Korea. By Robert G. Webb,
J. Knox Jones, Jr., and George W. Byers. Pp. 149-173. January
31, 1962.
3. A new species of frog (Genus Tomodactylus) from western
México. By Robert G. Webb. Pp. 175-181, 1 figure in text. March
7, 1962. 4. Type specimens of amphibians and reptiles in the
Museum of Natural History, the University of Kansas. By William
E. Duellman and Barbara Berg. Pp. 183-204. October 26, 1962.
5. Amphibians and Reptiles of the Rainforests of Southern El
Petén, Guatemala. By William E. Duellman. Pp. 205-249, plates
7-10, 6 figures in text. October 4, 1963.
6. A revision of snakes of the genus Conophis (Family
Colubridae, from Middle America). By John Wellman. Pp. 251-295,
9 figures in text. October 4, 1963.
7. A review of the Middle American tree frogs of the genus
Ptychohyla. By William E. Duellman. Pp. 297-349, plates 11-18,
7 figures in text. October 18, 1963. 50 cents.
*8. Natural history of the racer Coluber constrictor. By Henry
S. Fitch. Pp. 351-468, plates 19-22, 20 figures in text.
December 30, 1963. $1.00.
9. A review of the frogs of the Hyla bistincta group. By
William E. Duellman. Pp. 469-491, 4 figures in text. March 2,
1964.
10. An ecological study of the garter snake, Thamnophis
sirtalis. By Henry S. Fitch. Pp. 493-564, plates 23-25, 14
figures in text. May 17, 1965.
11. Breeding cycle in the ground skink, Lygosoma laterale. By
Henry S. Fitch and Harry W. Greene. Pp. 565-575, 3 figures in
text. May 17, 1965.
12. Amphibians and reptiles from the Yucatan Peninsula, México.
By William E. Duellman. Pp. 577-614, 1 figure in text. June 22,
1965.
13. A new species of turtle, Genus Kinosternon, from Central
America, by John M. Legler. Pp. 615-625, pls. 26-28, 2 figures
in text. July 20, 1965.
14. A biogeographic account of the herpetofauna of Michoacán,
México. By William E. Duellman. Pp. 627-709, pls. 29-36, 5
figures in text. December 30, 1965.
15. Amphibians and reptiles of Mesa Verde National Park,
Colorado. By Charles L. Douglas. Pp. 711-744, pls. 37, 38, 6
figures in text. March 7, 1966.
Index. Pp. 745-770.
Vol. 16.
1. Distribution and taxonomy of Mammals of Nebraska. By J. Knox
Jones, Jr. Pp. 1-356, pls. 1-4, 82 figures in text. October 1,
1964. $3.50.
2. Synopsis of the lagomorphs and rodents of Korea. By J. Knox
Jones, Jr., and David H. Johnson. Pp. 357-407. February 12,
1965.
3. Mammals from Isla Cozumel, Mexico, with description of a new
species of harvest mouse. By J. Knox Jones, Jr., and Timothy E.
Lawlor. Pp. 409-419, 1 figure in text. April 13, 1965.
4. The Yucatan deer mouse, Peromyscus yucatanicus. By Timothy
E. Lawlor. Pp. 421-438, 2 figures in text. July 20, 1965.
5. Bats from Guatemala. By J. Knox Jones, Jr. Pp. 439-472.
April 18, 1966.
More numbers will appear in volume 16.
Vol. 17.
1. Localities of fossil vertebrates obtained from the Niobrara
Formation (Cretaceous) of Kansas. By David Bardack. Pp. 1-14.
January 22, 1965.
2. Chorda tympani branch of the facial nerve in the middle ear
of tetrapods. By Richard C. Fox. Pp. 15-21, May 22, 1965.
3. Fishes of the Kansas River System in relation to
zoogeography of the Great Plains. By Artie L. Metcalf. Pp.
23-189, 4 figures in text, 51 maps. March 24, 1966.
4. Factors affecting growth and reproduction of channel
catfish, Ictalurus punctatus. By Bill A. Simco and Frank B.
Cross. Pp. 191-256, 13 figures in text. June 6, 1966.
5. A new species of fringe-limbed tree frog, genus Hyla, from
Darién, Panamá. By William E. Duellman. Pp. 257-262, 1 figure
in text. June 17, 1966.
6. Taxonomic notes on some Mexican and Central American hylid
frogs. By William E. Duellman. Pp. 263-279. June 17, 1966.
7. Neotropical hylid frogs, genus Smilisca. By William E.
Duellman and Linda Trueb. Pp. 281-375, pls. 1-12, 17 figures in
text. July 14, 1966.
8. Birds from North Borneo. By Max C. Thompson. Pp. 377-433, 1
figure in text. October 27, 1966.
9. Natural history of cottonmouth moccasin, Agkistrodon
piscivorus (Reptilia). By Ray D. Burkett. Pp. 435-491, 7
figures in text. October 27, 1966.
More numbers will appear in volume 17.
*** End of this LibraryBlog Digital Book "Natural History of Cottonmouth Moccasin, Agkistrodon piscovorus (Reptilia)" ***
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