Distance betweenbase of fangsDistance betweenfang puncturesSnout-ventlength7.713.04008.714.057510.022.552611.018.0-19.059012.018.079313.017.0, 20.0558, 61215.523.580016.024.0800
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 ofthe 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 (includingNatrix cyclopion,N. erythrogaster,N. rhombifera, andN. 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.)
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.
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.
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 ofA. p. leucostomain 50 Millimeter Size Classes.
Snout-ventlengthNumber ofgravid femalesTotal numberin size classPercentagegravid450-49931421.4500-54971741.2550-59981747.1600-6495771.4650-6992922.2700-7492366.7750-79911100.0850-89911100.0Totals296942.0
Increase in length of testes appears to be correlated with length of the individual rather than cyclic reproductive periods (Fig. 4).
Fig. 4. Length of testes in cottonmouths of various sizesFig. 4. Length of testes in cottonmouths of various sizes(·—left;°—right ). The right testis is always longer than the left.
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 ofA. p. piscivorus, from Florida, that produced broods of 14 and 12 young in two consecutive years.
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.
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.
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 embryosper 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 lengthin millimetersNumberin sampleNumber of ova,average and extremes450-549104.1 (2 to 7)550-649114.9 (1 to 8)650-74946.3 (4 to 8)750-84915850-949114
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.
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.
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 centof 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.
Fig. 5. Composition of a group of cottonmouthsFig. 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.
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 ofA. p. piscivorusreported by Wharton (1960:127) that averaged 338 millimeters total length and 28.7 grams. The yolk of one youngpiscivoruswas 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.
Agein daysSnout-vent length / tail length—weight in gramsFemale No. 1Female No. 2Male2185/40—11.1185/40—10.1185/40—10.07192/40—190/40—189/40—22195/40—10.3200/41.5—10.6197/40—80204/40—11.7203/42—10.4218/48—14.388....204/44—....143215/40.5—13.3....225/48—15.1
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 inHeterodon.
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 innatesize 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 ofindividualsTotal lengthin millimetersEstimated agein monthsEstimated growthfrom preceding yearin millimeters19260-2987-82511312-33719-204540355-48531-3295±83500-100043-44+?
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.) inA. p. piscivorusand 54 inches (1370 mm.) inA. p. leucostoma.
Fig. 6. Head length ( ? ) and head width ( ? )Fig. 6. Head length (°) 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 venomto 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).
Fig. 7. Tail length expressed as a percentage of snout-vent lengthFig. 7. Tail length expressed as a percentage of snout-vent length of living and preserved cottonmouths (·—males;°—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 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 oldstratum corneumfrom 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 inthis 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 ofcloudinessof eyesTime betweenclearing andsheddingTime from beginningof cloudinessuntil shedding56117310--6--65384610731056115387--7310X5.4X3.8X9.0
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.
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 exuviationsin 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 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-millimeterRana pipiensthat 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.
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]."
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 grownRana catesbeiana, several foot-long pickerel ... dead fish if placed in a pan of water....Natrix sipedon fasciataandMasticophis flagellum... rats.... Toads and largeEumeces laticepswere 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 intermediawas the most abundant food item in both volume and occurrence. Frogs of the genusRanaranked second. Together, these two items comprised almost2/3of the food of the snakes. The other food items were distributed among the fishes, reptiles, and other amphibians [oneRanatadpole included]." (Based on 42 samples—Barbour, 1956:37.)Illinois: (Based on 84 samples—Klimstra, 1959:5.)Food ItemPer cent Frequencyof OccurrencePer centVolumePisces39.331.9Amphibia36.926.0Reptilia25.018.2Mammalia30.917.9Gastropoda17.81.0Miscellaneous25.05.0(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; 25Rana pipiens; 16Rana clamitans; 7Acris; 4Natrix 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, mostlyRana 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.)
Georgia: "... full grownRana catesbeiana, several foot-long pickerel ... dead fish if placed in a pan of water....Natrix sipedon fasciataandMasticophis flagellum... rats.... Toads and largeEumeces laticepswere 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 intermediawas the most abundant food item in both volume and occurrence. Frogs of the genusRanaranked second. Together, these two items comprised almost2/3of the food of the snakes. The other food items were distributed among the fishes, reptiles, and other amphibians [oneRanatadpole included]." (Based on 42 samples—Barbour, 1956:37.)
Illinois: (Based on 84 samples—Klimstra, 1959:5.)
Food ItemPer cent Frequencyof OccurrencePer centVolumePisces39.331.9Amphibia36.926.0Reptilia25.018.2Mammalia30.917.9Gastropoda17.81.0Miscellaneous25.05.0(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; 25Rana pipiens; 16Rana clamitans; 7Acris; 4Natrix 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, mostlyRana 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 severaldistinct 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 ofLepomiseach 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).