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 cottonmouths that 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.
Defense and Escape
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 deg. 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 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 deg. 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
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.
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 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 definitely initiated because
of competition 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 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.
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 oreganus_) and the massasauga (_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 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-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 relationship to size or sex 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
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. 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
Glass (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
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.
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 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.
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, 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.