Part 4

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.