Natural History of Cottonmouth Moccasin, Agkistrodon piscovorus (Reptilia) Part 5

Neill (1947:205) reported one case in which a cottonmouth used the "body blow" defense, described for _Crotalus_ by 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"

"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 apparently connected with courts.h.i.+p 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 s.e.xually 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 courts.h.i.+p 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.

Combat Dance

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 courts.h.i.+p behavior until the partic.i.p.ants were examined and found to be males. Carr and Carr (1942:1-6) described one such instance in two cottonmouths as courts.h.i.+p. In their observations, as well as those of others, copulation was never observed following the "dance" but was a.s.sumed to be the ultimate goal. After the discovery that only males partic.i.p.ated, it was suggested that combat involved compet.i.tion 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 h.o.m.os.e.xuality. One case of h.o.m.os.e.xual mating among cottonmouths was reported (Lederer, 1931:651-653), but the incomplete description seems to be of normal courts.h.i.+p 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 definitely initiated because of compet.i.tion for food. More observations are needed before the significance of the combat can be fully understood.

THE VENOM

Properties of the Venom

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 quant.i.ties. 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 const.i.tuents 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 r.e.t.a.r.d 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 quant.i.ties 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.

Venom Yield and Toxicity

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 group of 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 of _Micrurus fulvius_ and _Crotalus 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) rated _C. adamanteus_ venom 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 orega.n.u.s_) and the ma.s.sasauga (_S.

catenatus_). He found _A. bilineatus_, _C. durissus_, and _C. v.

lutosus_ to 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 orega.n.u.s_, 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-blooded animals, which are less susceptible to venoms than warm-blooded animals, are thought to have highly toxic venoms. This explanation accounts for the powerful venom of _Sistrurus 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 tests _C. adamanteus_ held places 1, 2, 3, 12, and 16; _Bothrops atrox_ held places 4, 9, 10, and 13; and _A. piscivorus_ held places 5, 7, 8, and 15. Places 6, 11, and 14 were held by three individuals of different species. No relations.h.i.+p to size or s.e.x was indicated by the results of this experiment.

Susceptibility of Snakes

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 of _S. miliarius_ receiving 8.3 milligrams per ounce died in about ten hours, while a _C. durissus_ receiving 12.5 milligrams per ounce succ.u.mbed 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. A _Lampropeltis calligaster_ injected with _A. contortrix_ venom (0.767 milligrams per gram) died five days following the injection. This amount was more than twice the amount of _A. piscivorus_ venom injected into a _L. getulus_ by Allen (1937) in which the snake showed no ill effects. Keegan and Andrews (_loc. cit._) stated that success in overpowering and eating poisonous snakes by _Lampropeltis_ and _Drymarchon_ may be due to the ability to avoid bites rather than to immunity to the venom. However, Rosenfeld and Gla.s.s (1940) demonstrated that the plasma of _L. g. getulus_ had 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 ma.s.sasaugas, 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 cla.s.ses. The studies to date have been on far too few individuals to allow statistical a.n.a.lyses to be accurate.

THE BITE

Effects of the Bite

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 ident.i.ty (see Dent.i.tion). 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 cla.s.sification 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.

Treatment

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, pota.s.sium 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.