FOOD HABITS
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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.)
Food Item Per cent Frequency of Occurrence Per cent 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).
Food Items Number of samples in which item occurred Percent frequency of occurrence Estimated weight in grams Estimated percentage by bulk
Fish (7) 13.2 18.4
Esox sp. 1 20
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.