Food ItemsNumber ofsamples inwhich itemoccurredPercentfrequencyofoccurrenceEstimatedweightingramsEstimatedpercentagebybulkFish(7)13.218.4Esoxsp.120Lepomissp.215Unidentified4Amphibians(12)23.020.4Scaphiopus hurteri113Acris crepitans24Hyla cinerea212Hyla versicolor112Rana catesbeiana120Rana pipiens315Unidentified2Reptiles(15)28.429.9Pseudemys scripta215Anolis carolinensis16Eumeces fasciatus17Lygosoma laterale25Natrixsp.110Natrix erythrogaster210Agkistrodon piscivorus220Crotalussp.130Unidentified snakes3Birds(4)7.618.6Anhinga anhinga(juv.)160Egret (head and neck)120Passeriformes220Mammals(6)11.312.7Blarina brevicauda112Cricetinae518Unidentified(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 bonescould 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 aHyla 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-inchLepomis, and the other had hair in the intestine and the head and neck of an adult egret in the stomach.
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 byL. 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.
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 (Ochetosomasp.) 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 (Kalicephalussp.) 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 (Ophiotaeniasp.) 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.
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.
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 lateOctober or early November, at which time the daily maximum temperature is about 15° and the minimum is about 0°. Indications are that in the northern part of its range the annual activity cycle of the cottonmouth resembles that of the copperhead in northeastern Kansas. Klimstra (1959:2) captured cottonmouths from April to October in southern Illinois. Barbour (1956:36) collected large numbers of them in early April in Kentucky and stated that they migrate from swamps to wooded hillsides in late August and early September. Spring migrations begin after a few consecutive warm days in March. In northern Oklahoma cottonmouths have been found along the Verdigris River as early as March, suggesting that a few winter in crayfish holes and mammal burrows. The majority of individuals found in this area were at denning sites along cliffs above the river and emerged later than those near the river (Dundee and Burger, 1948:1-2). In Virginia cottonmouths have been seen as early as March 5 (Martin and Wood, 1955:237) and as late as December 4. They have been observed in migration from the swamps of the barrier beach to the mainland in late October and early November in southeastern Virginia (Wood, 1954a:159). According to Neill (1947:204), the cottonmouth tolerates lower temperatures than do most snakes in Georgia and is one of the last to go into hibernation. Allen and Swindell (1948:4) stated that cottonmouths usually bask during the mornings of the cooler months in Florida, but they mentioned nothing of denning such as occurs farther north. Although winter aggregations occur in the northern parts of the range, I have never seen such aggregations in the South. However, in one instance related to me by a reliable observer, seven cottonmouths were found together on a creek bank near the Gulf Coast in early spring.
During late summer and early autumn, fat is deposited in lobes in the lower abdomen in preparation for the period of winter quiescence. Gravid females usually do not feed so frequently or so much as other snakes, because they tend to become inactive as the ova develop. Whether or not females feed heavily after parturition and previous to denning is not known. Peaks of activity in autumn may be caused by final attempts to feed before denning and by the appearance of large numbers of newborn young. The young usually have from one to two months in which to feed before the advent of cold weather. According to Barbour's (op. cit.:38) findings, the young probably feed before hibernation because they grow substantially in winter. For those that do not feed, the rate of survival is perhaps much lower.
In preparation for winter, cottonmouths migrate inland, usually to dry forested hillsides where they den, commonly among rocks at the tops of bluffs, along with several other species of snakes. In such aggregations there is no hostility and each individual may derive benefit from contact with others by which favorable conditions of temperature and humidity are maintained.
Neill (1947:204) has found many specimens in winter by tearing bark from rotting pine stumps on hillsides overlooking lakes or streams. On cold days they evidently retreat below the surface, while on warm days they lie just below the bark or emerge and bask. Neill believes that the use of stumps by cottonmouths is an innate pattern of behavior, because of the large number of young-of-the-year found in such surroundings. Cottonmouths were observed in winter also under logs and stumps by Allen (1932:17). I have twice observed cottonmouths crawling into crayfish burrows along the Gulf Coast of Texas, and suppose they are used as denning sites to some extent.
The diel cycle of activity of cottonmouths is of necessity closely related to the seasonal cycle. Since optimal temperatures determine activity, the diel cycle varies greatly from time to time. It has been well established that cottonmouths, like most other crotalids and many snakes of other families, prefer nocturnal to diurnal activity, even though the temperature may be less favorable at night. This preference is correlated with increased nocturnal activity of frogs and reptiles that constitute the principal food supply.
During spring and autumn, activity is more restricted to the day and long periods of basking occur. However, as hot weather approaches, basking occurs mainly in the morning and evening and activity becomes primarily nocturnal. But, in well shaded, moist forests, cottonmouths feed actively in the daytime.
Availability of food also has an important influence upon activity. Allen and Swindell (op. cit.:5) stated that moccasins congregate around drying ponds and feed on dying fish until the moccasins can hold no more. They then usually stay nearby as long as food remains. In an area of the Stephen F. Austin Experimental Forest near Nacogdoches, Texas, many cottonmouths journey daily to and from a swamp and a dry field, evidently to feed on rodents inhabiting the area. Ten individuals captured along a snake-proof fence that was built 30 yards from the swamp were found lying coiled along the fence after 4:30 p.m., at which time the area was shaded. On another occasion, I captured a large cottonmouth that was feeding upon dying fish in a drying pool about 10:30 a.m. on August 19, 1962.
Because of the aquatic habits of the cottonmouth, relative humidity probably has little influence on the snake's activity. However, cottonmouths are more restricted to the vicinity of water in dry weather than during rains or muggy weather when many of their natural prey species also move about more freely. Increased activity on cloudy days may result from protection from long exposure to sunshine. Torrential rains and floods, such as those following hurricanes along the Gulf and Atlantic coasts of the southeastern United States, bring out quantities of snakes of all species. Rattlesnakes and cottonmouths in particular are killed by the thousands at these times because they seek shelter in human habitations. However, these are unusual circumstances and do not reflect voluntary activity as a result of preferences.
Thermal reactions of reptiles were classified by Cowles and Bogert (1944) into several categories. For each species there is a basking and normal activity range limited by the voluntary minimum and voluntary maximum at which the animal seeks shelter. Beyond this normal range are the critical thermal minimum and critical thermal maximum (C. T. M.) at which effective locomotion is prevented. The lethal minimum and maximum are those temperatures at which short exposure produces irreparable damage, and death inevitably results. These classifications are modified somewhat by seasonal or laboratory acclimation or by the physiological state of the animal. The C. T. M. of five cottonmouths was determined by placing each individual in an enclosed area and heating it with an infrared lamp. Cloacal temperatures were taken with a Schultheis quick-recording thermometer as soon as the snake could no longer right itself when placed on its back. All temperatures were in degrees Celcius. The C. T. M. averaged 39.2° (38.0° to 40.0°). A temperature of 38.0° was lethal to one individual. These cottonmouths hadbeen 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.
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.
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.
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.
The number of different opinions expressed in the literature concerning the cottonmouth's disposition is not at all surprising. As with any species there is a wide range of individual temperament, which is affected by many factors. The cottonmouth is considered by some writers to be docile while others consider it to be highly dangerous. Allen and Swindell (1948:7) described the variability in temperament, even among individuals. They wrote: "On rare occasions, moccasins are found which will attack. A perfectly docile snake will turn and bite viciously without any apparent reason." They also recounted a case in which a cottonmouth was kept as a pet for six years, being allowed the freedom of the house. Smith and List (1955:123) found them "... surprisingly docile in the gulf region [Mississippi], displaying none of the pugnacity of more northern cottonmouths." Smith (1956:310) stated: "Unlike the copperhead, cottonmouths are pugnacious; their powerful jaws, long fangs, vicious disposition and potent venom make them a very dangerous animal."
My own observations are in general agreement with the statements of Allen and Swindell (loc. cit.). In my encounters with cottonmouths, I have never found any aggressive individuals except for three juveniles that were born in captivity. In their first three days in the laboratory these juveniles were observed to strike repeatedly whenever anyone entered the room. After this short period of aggressiveness, however, they slowly became more docile. The disposition shown by the newborn young is clearly an innate behavioral pattern that undoubtedly has a direct relationship to survival. The majority of cottonmouthsthat I have approached in the field have moved swiftly to seek refuge in nearby water; a few have remained motionless as I approached, and one showed the typical threat display. Upon capture and handling, they react similarly to other pit-vipers by opening and closing the mouth and erecting the fangs in an attempt to bite. They often bite through the lower jaw and eject venom at this time as well as when the mouth is open. Of more than a dozen individuals kept in captivity, four were particularly difficult to handle whereas another was extremely docile. It was almost never found in aggregations with the other snakes and did not struggle or attempt to bite when handled. The majority remained unpredictable in disposition, usually appearing docile and lazy but capable of extremely rapid movements when disturbed.
The typical threatening posture of rattlesnakes is all but lacking in the cottonmouth, which relies primarily on concealing coloration or nearness to water for escape. When approached, it usually plunges into nearby water or remains motionless with the head held up at a 45° angle and the mouth opened widely exposing the white interior. The tail is sometimes vibrated rapidly and musk is expelled. This threat display is unique to cottonmouths; although it does not attract as much attention as the display of rattlesnakes, it is probably an effective warning to most intruders at close range.
Neill (1947:205) reported one case in which a cottonmouth used the "body blow" defense, described forCrotalusby Cowles (1938:13), when approached by a king-snake,Lampropeltis getulus. In this unusual posture the anterior and posterior portions of the body are held against the ground and the middle one-fourth to one-third of the body is lifted up and used in striking the intruder. This same defense posture also was observed in rattlesnakes when presented with the odor of the spotted skunk,Spilogale phenax. However, the "king-snake defense posture" is probably not a well-established behavioral pattern in the cottonmouth, for it sometimes feeds upon king-snakes. I observed the killing and devouring of a cottonmouth by a speckled king-snake,L. g. holbrooki; the only attempts to escape were by rapid crawling and biting.
Cottonmouths often squirt musk as a defensive action. The tail is switched back and forth, and musk is emitted from glands on each side of the base of the tail. The fine jets of musk are sprayed upward at about 45° angles for a distance of nearly five feet. How often this defense mechanism is used against other animals is not known, but the musky odor can frequently be detected in areas where cottonmouths are common. The odor is repulsive and, if concentrated, can cause nausea in some individuals. To me, the scent is indistinguishable from that of the copperhead.
"Head bobbing" in snakes has been described frequently in the literature, and many interpretations have been advanced to explain its occurrence. One of the earlier accounts was that of Corrington (1929:72) describing behavior of the corn snake,Elaphe guttata. Characteristic bobbing occurred when the snake was cornered, and seemingly the purpose was to warn or frighten foes. Neill (1949:114-115) mentioned the jerking or bobbing of the head in several species of snakes including the cottonmouth, and remarked that "it is apparentlyconnected with courtship and with the recognition of individuals." According to Munro (1950:88), "head bobbing" appears to be a sign of annoyance in some instances but is usually concerned with reproduction and individual recognition. Richmond (1952:38) thought that many types of head movements among not only reptiles but also birds and some mammals are a result of poor vision and serve "to delimit and orient an object that for lack of motion is otherwise invisible." Head movements undoubtedly occur in animals to facilitate accommodation, but it is obvious from Richmond's conclusions that he has never observed "head bobbing" in snakes. The term itself is grossly misleading and should be discarded. Mansueti (1946:98) correctly described the movements as spastic contractions of the body. I have observed numerous instances of these movements in cottonmouths, copperheads, and rat snakes (Elaphe obsoleta); and in no case has the movement resembled a head bob as is described in lizards and other animals. The movement appears to be a result of a nervous or sexually excited state and consists of highly spastic contractions confined to the anterior part of the snake most of the time but affecting the entire body on some occasions.
I found the response to be most common among cottonmouths in confinement when food was introduced to a cage containing several individuals (increasing the tendency to strike at a moving object) and when an individual was placed back in the cage after being handled. At these times the snakes that were inactive began to jerk for a few seconds. When the snake is in this seemingly nervous state, the same response is elicited by another snake crawling over it. At other times the movement of one individual causes no such response. The jerking movements appear to be released by the recognition of a nervous state in another individual and may serve to protect the jerking individual from aggressive advances of the former.
Where courtship is involved, the jerking motions are made in conjunction with writhing of the male and do not result from the same type of releaser described above.
The so-called combat dance between male snakes has long been known, but its significance is still poorly understood. It was for many years believed to be courtship behavior until the participants were examined and found to be males. Carr and Carr (1942:1-6) described one such instance in two cottonmouths as courtship. In their observations, as well as those of others, copulation was never observed following the "dance" but was assumed to be the ultimate goal. After the discovery that only males participated, it was suggested that combat involved competition for mates, but the "dance" has been observed at times other than the breeding season (Ramsey, 1948:228).
Shaw (1948:137-145) discussed the combat of crotalids in some detail but drew no conclusions as to the cause of the behavior. Lowe (1948:134) concluded with little actual evidence that combat among male snakes is solely for territorial purposes. Shaw (1951:167) stated that combat may occur as a possible defense against homosexuality. One case of homosexual mating among cottonmouths was reported (Lederer, 1931:651-653), but the incomplete description seems to be of normal courtship procedure except that the "female" tried to avoid the male. Two instances of combat observed between timber rattlesnakes (C. h. horridus) by Sutherland (1958:23-24) were definitelyinitiated because of competition for food. More observations are needed before the significance of the combat can be fully understood.
The venom and poison apparatus have developed primarily as a means of causing rapid death in small animals that are the usual prey. As a protective device against larger enemies, including man, the venom may have some value; but this was probably unimportant in the evolution of the poison mechanism. A secondary function of the venom is to begin digestion of tissues of the prey. Since food is swallowed whole, injection of digestive enzymes into the body cavity enhances digestion of the prey.
Kellogg (1925:5) described venom as a somewhat viscid fluid of a yellowish color and composed of 50 to 70 per cent proteins, the chief remaining components being water and carbohydrates, with occasional admixtures of abraded epithelial cells or saprophytic microorganisms. Salts, such as chlorides, phosphates of calcium, magnesium, and ammonium, occur in small quantities. Each of the components of snake venom has a different effect on the body of the victim. It was at first believed that there were two types of venoms: neurotoxic, which acts upon nervous tissue; and haemotoxic, which acts on blood and other tissues. It has since been found that venoms are composed of varying mixtures of both types. Fairley (1929:301) described the constituents of venom as: (1) neurotoxic elements that act on the bulbar and spinal ganglion cells of the central nervous system; (2) hemorrhagins that destroy the lining of the walls of blood vessels; (3) thrombose, producing clots within blood vessels; (4) hemolysins, destroying red blood corpuscles; (5) cytolysins that act on leucocytes and on cells of other tissues; (6) elements that retard coagulation of the blood; (7) antibactericidal substances; and (8) ferments that prepare food for pancreatic digestion. Elapid snakes tend to have more of elements 1, 4, and 6 in their venoms, while viperids and crotalids, of which the cottonmouth is one, have higher quantities of elements 2, 3, and 5. Kellogg (loc. cit.) stated that venom of cottonmouths contains more neurotoxin than that of rattlesnakes and not only breaks down the nuclei of ganglion cells but also produces granular disintegration of the myelin sheath and fragmentation of the conducting portions of nerve fibers.
Thus, venoms contain both toxic elements and non-toxic substances that promote rapid spreading of the venom through the body of the victim. Jacques (1956:291) attributed this rapid spreading to the hyaluronidase content of venoms.
One of the most important yet undeterminable factors of the gravity of snakebite is the amount of venom injected into the victim. Since this volume varies considerably in every bite, attempts have been made to determine the amount and toxicity of venom produced by each species of poisonous snake. Individual yield is so variable that a large number of snakes must be milked in order to determine the average yield. Even then there remains an uncertainty as to how this amount may compare with that injected by a biting snake.
Wolff and Githens (1939b:234) made 16 venom extractions from a groupof cottonmouths in a two-year period. The average yield per snake fluctuated between 80 and 237 milligrams (actual weight), and toxicity measured as the minimum lethal dose for pigeons varied from 0.05 to 0.16 milligrams (dry weight). No decrease in yield or toxicity was evident during this period. Another group of cottonmouths from which venom was extracted over a period of five years also showed no decrease in yield or toxicity. Of 315 individual extractions the average amount obtained from each individual was 0.55 cubic centimeters of liquid or 0.158 grams of dried venom (28.0 per cent solids). The minimum lethal dosage (M. L. D.) which was determined by injecting intravenously into 350-gram pigeons was found to be 0.09 milligrams (dry weight). Each snake carried approximately 1755 M. L. D.'s of venom.
The record venom extraction for the cottonmouth was 4.0 cubic centimeters (1.094 grams dried venom) taken from a five-foot snake which had been in captivity for 11 weeks and milked five weeks earlier (Wolff and Githens, 1939a:52). The average yield of venom of cottonmouths is about three times the average yield reported for copperheads by Fitch (1960:256), a difference correlated with the greater bulk and relatively large head of the cottonmouth.
Allen and Swindell (1948:13) stated that cottonmouth venom rates third in potency, compared drop for drop to that ofMicrurus fulviusandCrotalus adamanteus. Freshly dried cottonmouth venom tested on young white rats showed the lethal dose to be from 23 to 29 milligrams per kilogram of body weight. The venom of 11 one-week-old cottonmouths was found to be more potent than that of adult males. Githens (1935:171) ratedC. adamanteusvenom as being weaker than that of the copperhead (A. contortrix), which he rated only slightly lower than cottonmouth venom. The crotalids which he ranked more toxic than cottonmouths are: the Pacific rattlesnake (C. viridis oreganus) and the massasauga (S. catenatus). He foundA. bilineatus,C. durissus, andC. v. lutosusto have the same toxicity as cottonmouths. Minton (1953:214) found that the intraperitoneal "lethal dose 50" (the dose capable of killing half the experimental mice receiving injections of it) was 6.36 milligrams per kilogram for copperheads. However, in later publications Minton (1954:1079; 1956:146) reported that the "lethal dose 50" for copperheads was 25.65 milligrams. Approximately the same potency was determined for cottonmouths. Several rattlesnakes that he tested showed a higher toxicity than copperheads or cottonmouths.
Criley (1956:378) found the venom of copperheads to be 6.95, nearer Minton's earlier estimate, and rated cottonmouth venom as being twice as toxic as that of copperheads. The relative toxicities of other crotalids tested, considering the cottonmouth to be one unit, were:C. basiliscus, 0.3;A. contortrix, 0.5;C. viridis oreganus, 1.4;A. bilineatus, 2.2;C. adamanteus, 2.3;C. v. viridis, 3.2;C. durissus terrificus, 27.5.
It can be seen from the above examples that toxicity of venoms and the resistance of the animal receiving an injection of venom is highly variable. Possibly the venom of each species of snake has greatest effect on animals of the particular group relied on for food by the snake. If that is so, the venom of cottonmouths would be expected to be more toxic when tested on fish, reptiles, and amphibians than on birds and mammals. Likewise, the venom of most species of rattlesnakes would be expected to be more virulent when injected into mammals than when injected into lower vertebrates. But, according to Netting (1929:108), species of rattlesnakes that prey on cold-bloodedanimals, which are less susceptible to venoms than warm-blooded animals, are thought to have highly toxic venoms. This explanation accounts for the powerful venom ofSistrurus catenatus; and, in this respect, venom of cottonmouths should be highly toxic also. However, no clear-cut trends have been shown in most cases. Allen (1937) injected 250-gram guinea pigs with 4 milligrams of venom of various poisonous snakes. Survival time was recorded in order to indicate the relative potency of the venoms. Of 16 such testsC. adamanteusheld places 1, 2, 3, 12, and 16;Bothrops atroxheld places 4, 9, 10, and 13; andA. piscivorusheld places 5, 7, 8, and 15. Places 6, 11, and 14 were held by three individuals of different species. No relationship to size or sex was indicated by the results of this experiment.
Numerous experiments have been conducted to determine the susceptibility of various snakes to venom. The majority of these experiments were performed to learn whether or not venomous snakes were immune to their own poison. Conant (1934:382) reported on a 30-inch cottonmouth that killed two Pacific rattlesnakes and another cottonmouth. One rattlesnake was bitten on the tail and the other on or near the head and partially swallowed. Gloyd (1933:13-14) recorded fatal effects to a rattlesnake from the bite of a cottonmouth. He also reported on the observations of three other crotalids bitten by themselves or other snakes, from which no harmful effects were observed. Allen (1937) injected several snakes with dried cottonmouth venom which was diluted with distilled water just before each injection. Four cottonmouths receiving 9, 18, 19, and 20 milligrams of venom per ounce of body weight survived, while another receiving 18.7 milligrams per ounce died after three hours. A specimen ofS. miliariusreceiving 8.3 milligrams per ounce died in about ten hours, while aC. durissusreceiving 12.5 milligrams per ounce succumbed in 45 minutes. An alligator receiving 6 milligrams per ounce died in 14 hours. Even the snakes that survived showed some degree of swelling.
The studies of Keegan and Andrews (1942:252) show that king-snakes are sometimes killed by poisonous snakes. ALampropeltis calligasterinjected withA. contortrixvenom (0.767 milligrams per gram) died five days following the injection. This amount was more than twice the amount ofA. piscivorusvenom injected into aL. getulusby Allen (1937) in which the snake showed no ill effects. Keegan and Andrews (loc. cit.) stated that success in overpowering and eating poisonous snakes byLampropeltisandDrymarchonmay be due to the ability to avoid bites rather than to immunity to the venom. However, Rosenfeld and Glass (1940) demonstrated that the plasma ofL. g. getulushad an inhibiting effect on the hemorrhagic action on mice of the venoms of several vipers.
One of the more extensive studies on effects of venoms on snakes is that by Swanson (1946:242-249). In his studies freshly extracted liquid venom was used. His studies indicated that snakes are not immune to venom of their own kind or to closely related species. Copperhead venom killed copperheads faster than did other venoms but took more time to kill massasaugas, cottonmouths, and timber rattlers. However, most of the snakes were able to survive normal or average doses of venom although they are not necessarily immune to it.
One of the major problems in comparing the data on toxicity of venom in studies of this type is that no standard method of estimating toxicity has been used. Swanson's (loc. cit.) amount of venom equalling one minim (M.L.D.?) ranged from 0.058 to 0.065 cubic centimeters. There were no different values given for each species, but the time that elapsed from injection of the venom to death represented the toxicity. There also was no attempt in his study to convert the amount of venom used into a ratio of the volume of venom per weight of snake, making the results somewhat difficult to interpret. Additional work in this field should provide for many injections into many individuals of several size classes. The studies to date have been on far too few individuals to allow statistical analyses to be accurate.
Factors determining the outcome of snakebite are: size, health, and species of snake; individual variation of venom toxicity of the species; age and size of the victim; allergic or immune responses; location of the bite; and the amount of venom injected and the depth to which it is injected. The last factor is one of the most variable, owing to (1) character and thickness of clothing between the snake and the victim's skin, (2) accuracy of the snake's strike, and (3) size of the snake, since a large snake can deliver more venom and at a greater depth than can a small snake.
Pope and Perkins (1944) demonstrated that pit-vipers of the United States bite as effectively as most innocuous snakes and that a careful study of the bite may reveal the location of the pocket of venom, size of the snake, and possibly its generic identity (see Dentition). The bite pattern of the cottonmouth as well as the other crotalids showed the typical fang punctures plus punctures of teeth on both the pterygoid and mandible. Even so, a varying picture may be presented because from one to four fang marks may be present. At times in the fang-shedding cycle three and even four fangs can be in operation simultaneously.
Various authors have attributed death of the prey to the following causes: paralysis of the central nervous system, paralysis of the respiratory center, asphyxiation from clotting of the blood, stoppage of the heart, urine suppression due to crystallized hemoglobin in the kidney tubules, dehydration of the body following edema in the area of the bite, or tissue damage. Mouths of snakes are reservoirs for infectious bacteria, which are especially prolific in damaged tissue. Bacterial growth is aided by the venom which blocks the bactericidal power of the blood.
Three grades in the severity of snakebite (I, minimal; II, moderate; and III, severe) were described by Wood, Hoback, and Green (1955). Parrish (1959:396) added a zero classification to describe the bite of a poisonous snake in which no envenomation occurred. Grade IV (very severe) was added by McCollough and Gennaro (1963:961) to account for many bites of the eastern and western diamondback rattlesnakes.
The first symptom of poisonous snakebite is an immediate burning sensation at the site of the bite. Within a few minutes the loss of blood into the tissues causes discoloration. Swelling proceeds rapidly and can become so great as to rupture the skin. Pain is soon felt in the lymph ducts and glands. Weakness,nausea, and vomiting may ensue at a relatively early stage. Loss of blood into tissues may spread to the internal organs. In conjunction with a rapid pulse, the blood pressure and body temperature can drop. Some difficulty in breathing can occur, especially if large amounts of neurotoxin are present in the venom. In severe cases the tension due to edema obstructs venous and even arterial flow, in which case bacteria may multiply rapidly in the necrotic tissue and gangrene can occur. Blindness due to retinal hemorrhages may occur. Symptoms of shock may be present after any bite.
Perhaps one of the most important factors in the outcome of snakebite is the treatment. Because of the variable reactions to snakebite, treatment should vary accordingly. Many methods have been proposed for treating snakebite, and there is disagreement as to which is the best. The list of remedies that have been used in cases of snakebite includes many that add additional injury or that possibly increase the action of the venom. The use of poultices made by splitting open living chickens and the use of alcohol, potassium permanganate, strychnine, caffeine, or injection of ammonia have no known therapeutic value, and may cause serious complications. The most important steps in the treatment of snakebite are to prevent the spread of lethal doses of venom, to remove as much venom as possible, and to neutralize the venom as quickly as possible.
It is generally agreed that the first step in snakebite treatment should be to place a ligature above the bite to restrict the flow of venom, and also to immobilize the patient as much as possible. The ligature should be loosened at least every fifteen minutes. The next steps are sterilization of the skin and the making of an incision through the fang punctures. As pointed out by Stahnke (1954:8), the incision should be made in line with the snake's body at the time of the bite, so as to account for the rearward curvature of the fangs and possibly to reach the deposition of venom. Many instruction booklets and first-aid guides have specified the length and depth of incision to be made, but the actual size and depth of the cut should depend upon the location of the bite. An "X" cut or connection of the fang punctures is likely to facilitate the spread of the venom. No cut should be made that would sever a large blood vessel or ligament.
Extensive damage is often caused by well-meaning individuals whose attempts at first aid result in brutally deep incisions and tourniquets applied too tightly and for too long a period of time; the resultant damage in many instances exceeds that of the bite itself (Stimson and Engelhardt, 1960:165). Stimson and Engelhardt also think that time should be sacrificed to surgical cleanliness, and incisions should not be made if a hospital can be reached within an hour.
The ligature-cryotherapy (L-C) method proposed by Stahnke (1953) has been severely criticized by other workers. He stated that the ligature should be tight enough to restrict completely the flow of venom until the temperature of the area can be lowered sufficiently to prevent any action of the venom. After 10 minutes the ligature may be removed and the bitten area kept immersed in a vessel of crushed ice and water. If the envenomized member is to be treated for more than four hours (which is the case with almost allpit-viper bites), it should be protected by placing it in a plastic bag. The venom action should be tested after 12 or more hours. This consists of a brief warming period to determine whether or not the action of the venom can be felt. The patient should be kept warm at all times; and the warming at the termination of treatment should be done gradually, preferably by allowing the water to warm slowly to room temperature.
Advocates of the L-C method warn against making incisions unless they are absolutely necessary, the theory being that each cut permits additional bacterial infection and does little good in removing venom. However, McCollough and Gennaro (1963:963) demonstrated that, in bites where the fangs had only slightly penetrated the skin, more than 50 per cent of the venom was removed in some instances if suction was started within three minutes after the injection. With deeper injection the amount of venom recovered sometimes reached 20 per cent of the dose. Stahnke suggested that an incision be made at the site of the bite only after the site has been refrigerated for at least 30 minutes.
Stimson and Engelhardt (loc. cit.) stated that two constricting bands should be used between the bite and the body and that cracked ice in a cloth should be applied to the bite before reaching a hospital. In addition, they suggested the following procedure. Rings of incisions should follow the swelling, and suction should continue for several hours. After the edema has receded, the limb should be wrapped in a towel containing crushed ice. Antivenin should be given only in severe cases. Calcium gluconate and gas gangrene antitoxin as well as antibiotics are helpful.
The most recent and up-to-date summary of snakebite treatment is that by McCollough and Gennaro (1963). Following is a brief summary of their suggestions:
1. Immobilization—Systemic immobilization is effected by body rest and locally by splinting the bitten area.
2. Tourniquet—A lightly occlusive tourniquet during a 30- to 60-minute period of incision and suction would seem to possess some advantages. In severe cases where medical attention is hours away, a completely occlusive tourniquet may be necessary to prevent death. Sacrifice of the extremity may be necessary for the preservation of life.
3. Incision and suction—Suction should begin three to five minutes after injection of venom if symptoms of poisoning are present. Incisions one-fourth inch to an inch long across each fang mark should be made in order to open the wound for more efficient suction. Multiple incisions are not useful for the removal of venom but may be employed under hospital conditions to reduce subcutaneous tensions and ischemia.
4. Cryotherapy—An ice cap over the site of the bite for relief of pain would seem to be permissible, especially prior to the administration of antivenin. It must be remembered that cooling during the administration of the antivenin radically reduces the access of the antiserum to the bite area.
5. Antivenin—Antiserum is the keystone to the therapy of snakebite. Careful evaluation of the severity of the bite and the patient's sensitivity should be made before the use of antivenin. In Grade II (moderate) bites, the intramuscular injection on the side of the bite may suffice. In Grades III (severe) and IV (very severe), shock and systemic effects require intravenous injection. In bites producing symptoms of this severity, antivenin must be given inamounts large enough to produce clinical improvement. Ten to 20 units may be necessary to prevent the relapse that sometimes occurs after small doses of antivenin. Permanent remission of swelling and interruption of necrosis are the therapeutic end point in the clinical use of the antiserum.
In all cases of snakebite where there is any doubt as to the snake's identity, it should be killed if possible and taken to the hospital for positive identification. In many instances of actual bites by poisonous snakes the only treatment needed was an injection of tetanus antitoxin or toxoid and sedation, because physical examination revealed no indication of poisoning (Stimson and Engelhardt,loc. cit.).
On July 29, 1963, at 8:20 a.m., I was treating a nine-month-old cottonmouth for mites. As I dropped the snake into a sink, it twisted its head and bit the tip of my right middle finger with one fang. The fang entered just under the fingernail and was directed downward, the venom being injected about five millimeters below the site of fang penetration. After placing the snake back in its cage, I squeezed the finger once to promote bleeding, wrapped a string around the base of the finger, and drove to Watkins Memorial Hospital on the University of Kansas campus. I began to feel a burning sensation in the tip of the finger almost immediately. Upon my arrival at the hospital, an additional ligature was placed around my wrist. At 8:30 a.m. a small incision was made in the end of the finger, which by this time was beginning to darken at the point of venom deposition. I sucked on the finger until 8:35 a.m., when a pan of ice water that I had requested was brought to me. No pain was felt except that caused by the ice. Fresh ice was added as needed to keep the temperature low. By 9:30 a.m. the finger had swollen and stiffened. At 10:00 a.m. the swelling had progressed to the index finger and back of the hand. I experienced difficulty in opening and closing the hand. Blood oozed slowly from the incision. A dull ache persisted and about every two to four minutes a sharp throb could be felt until nearly 11:00 a.m., when the pain diminished. The rate and intensity of throbbing increased whenever the hand was removed from the ice bath for more than a few seconds. Although only the hand was immersed, the entire forearm was cold. Pain was felt along the lymphatics on top of the arm when it was touched, and by 1:00 p.m. a slight pain could be felt in the armpit. Since swelling and pain were almost nonexistent by 2:00 p.m., I was permitted to leave. After walking to a nearby building, I again felt a burning sensation as the hand warmed. I made another ice bath and again immersed the hand in it until 4:10 p.m., at which time it was removed from the water. The pain and swelling began anew, and the hand was placed back in an ice bath from 5:30 p.m. until about 7:30 p.m. At this time cryotherapy was discontinued. From 10:00 p.m. to 12:00 midnight my legs twitched periodically, and pain could be felt in both armpits. A slight difficulty in breathing also was experienced for a short time. The acute pain and burning sensation remained in the finger until the following morning, but swelling progressed only as far as the wrist. The only discomfort that day was in the finger. The tip was darkened, the entire first digit red and feverish, and the lymphatics still painful when touched. By the third day the swelling had regressed. The incision itself was the main cause of discomfort, and the soreness at the site of the bite persisted for at least four days.
Although the L-C method of snakebite treatment has been vigorously attacked by many, there is still need of much more data before it can be unequivocally condemned or praised. It was preferred in the treatment of this bite because: I knew that envenomation was minimal and that there would be no need for antivenin; only one fang of a snake less than one foot long had entered the tip of the finger; the snake had bitten three frogs in the previoustwo days and had possibly used up a considerable amount of its venom; the venom was deposited at such a shallow depth that at least a portion of it could be removed by suction; and the wound bled freely even before suction was applied. The ice water was uncomfortably cold but was not cold enough to cause frostbite, a major objection to the L-C method. Ideally, fresh ice should be added little by little to replace that which is melting, and the immersed area should be protected from the water by a plastic bag. Pain and swelling can be minimized by cryotherapy, but I would recommend its use only in cases of mild poisoning such as the one described herein.