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 deg.
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 deg. C. and the minimum is about 4 deg. C., and
become dormant in late October or early November, at which time the
daily maximum temperature is about 15 deg. and the minimum is about 0 deg..
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 deg. (38.0 deg. to 40.0 deg.). A temperature of
38.0 deg. 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."