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The loss of a single snake, or a dozen snakes, or even a hundred in one year will probably not seriously impact the balance of a particular ecosystem, at least not in the long term. Most natural changes occur slowly, over prolonged periods, like the rhythm of the seasons or the process of aging, so that their effects are usually not immediately apparent. But it is clear that over time the cumulative consequences of snake bashing, coupled with habitat destruction and environmental pollution, have taken a heavy toll of most native serpents, as probably has the insidious and sometimes equally devastating damage inflicted by the imported fire ant. Although habitat degradation and pollution are the chief causes of decline in local serpent populations statewide, it is not our intention to address these issues at length, since the resolution of such threats resides largely in the political arena and is therefore beyond the scope of this book. This is not to suggest, however, that interested persons should avoid becoming involved with local or national conservation groups to influence government policy makers in wildlife conservation matters. Indeed, doing so is often the best way to achieve significant and lasting results.
But to anyone with a clutching fear of snakes (which includes most of us), any idea of conserving these creatures will seem ludicrous or, at the very least, a misplaced priority. What is the compelling reason for this antiserpent bias? If we can accept that the great majority of snakes are incapable of causing us serious harm and that by reason of their feeding habits most of them are beneficial to our interests, by what logic do we feel obliged to destroy them on sight? The obvious answer is that a great majority of us lack even a basic understanding of these essentially timid and benign animals.
Our information about them often comes from those whose bias, like our own, is based primarily on the same myths and misconceptions that have confounded the subject since ancient times. Although erroneous, such implausible tales pique our interest, and their telling makes for lively after-dinner conversation. Unfortunately, however, by masking the truth they make more difficult the task of getting to the facts. The challenge then is to present the facts about these generally innocuous animals in such a way that even the snake haters among us will see these reptiles for what they really are—not vengeful creatures lurking in the brush to ambush the next human victim but another life form no more villainous than any of the others. Indeed, the life of a snake is basically not much different from that of other animal species. Like them it must find food, reproduce, protect itself from its enemies, and maintain a comfortable body temperature in the face of the changing seasons. How serpents fulfill these life functions can be as interesting as the bizarre snake stories we often hear and accept as fact. Only when we can cast aside such misinformation and replace it with an objective view of our subjects are we likely to entertain the idea of conserving snakes. That, it seems to us, is where the conservation ethic begins.
Texas Threatened Snakes
Texas snakes that are currently listed as threatened by the state of Texas and or the United States Fish and Wildlife Service are given below. The reason for this particular list of snakes involves human development of land, water, and timber resources. In addition, those snakes whose distribution barely enters Texas may easily be exploited by commercial and/or private collectors, as well as by the developers of natural resources mentioned above.
- Cemophora coccinea copei (northern scarlet snake)
- Cemophora coccinea lineri (Texas scarlet snake)
- Coniophanes imperialis imperialis (black-striped snake)
- Crotalus horridus atricaudatus (canebrake rattlesnake)
- Drymarchon melanurus erebennus (Texas indigo snake)
- Drymobius margaritiferus margaritiferus (speckled racer)
- Leptodeira septentrionalis septentrionalis (northern cat-eyed snake)
- Opheodrys vernalis blanchardi (smooth green snake)
- Nerodia harteri harteri (Brazos water snake)
- Nerodia harteri paucimaculata (Concho water snake)
- Pituophis ruthveni (Louisiana pine snake
- Tantilla cucullata (Trans-Pecos black-headed snake)
- Trimorphodon vilkinsoni (Texas lyre snake)
Poisonous Snakes, Venom and Bite
To a large extent, our fear of snakes is based on the knowledge that a few of them are venomous and capable of causing us serious bodily injury and sometimes even death. This fear, while logical enough when based on the facts of the matter, is usually so exaggerated that it can become unreasonable or, in the extreme, even grotesque, leaving little or no opportunity for rational dialogue. Some people have such an overwhelming fear of snakes that getting them to talk about the animals that cause them so much mental anguish may be impossible without professional help. Psychologists explain that ophidiophobia is among the more difficult fears to overcome. Such practitioners estimate that more than 50 percent of our population experience some anxiety in the presence of snakes, and another 20 percent are terrified by them. Extreme examples of the latter include those who become terror-stricken when they so much as see the picture of a snake in a magazine, a book, or on television, and others who avoid outdoor activities altogether for fear of encountering a snake, even a harmless one. Sadly, most of these people retain their morbid fear for life. But there are hopeful signs that the other 50-plus percent—those with only a moderate fear of serpents—are slowly but surely being reduced in number as both public and private institutions and organizations concerned with natural history education reach ever more people with their hands-on programs. Probably at the forefront in molding such attitudinal changes are the country's zoological parks (and aquariums), which, through live exhibits and informal teaching programs, annually expose their nearly 120 million visitors to wildlife conservation messages. Science museums, nature centers, and wildlife organizations are fulfilling a similar role. As a direct result of such efforts, one encouraging sign of the change taking place in our attitude about snakes is the phenomenal growth of the pet-snake hobby; having gained prominence only about 20 years ago, it continues to expand at an accelerated pace, with devotees nationwide numbering in the many thousands.
Despite such progress, a great deal of apprehension and misunderstanding still exist among Texans about their native serpents. In the minds of most persons, snakes are still the enemy. They are seen as mysterious and menacing, to be killed wherever and whenever they are encountered. The truth is that snakes—even the dangerous ones—are fundamentally shy and retiring, more than willing to avoid a confrontation with humans by fleeing when given the chance. Only as a last resort will they bite in self-defense.
Our native venomous serpents do not typically display overtly offensive behavior; they nevertheless pose a potential risk for those engaged in outdoor activities. This is, after all, a large state with a diverse snake fauna, consisting of 72 species (by our count), 11 of which are considered dangerous to humans. Ranking the states by raw figures, Parrish (1964) estimated that Texas suffered more venomous snakebites in a single year than any other state nationwide, although when the number of such accidents was calculated per 100,000 residents, Texas ranked third, with an incidence rate of 14.70 percent, trailing behind North Carolina at 18.79 percent and Arkansas at 17.19 percent. Moreover, based on actual and projected snakebite incidents for 1958 and 1959, he estimated that approximately 1,408 snakebite victims were treated in Texas in each of those years, consisting of 784 inpatients and 624 outpatients. An average of only 2.4 fatalities occurred annually—a mortality rate of just one-fourth of 1 percent of those bitten. Even more encouraging are the mortality figures for the years 1978 through 1995, which according the Texas Department of Health, Bureau of Vital Statistics, averaged only one death a year. These figures hardly classify venomous snakebite as a high-mortality occurrence, at least in the United States. Outdoor hazards more likely to cause human death in Texas are the stings and bites of insects and arachnids, lightning strikes, hunting accidents involving firearms, and drownings.
Among our dangerous snake species, two in particular are responsible for the greatest number of bites inflicted on humans. They are the copperhead and the western diamond-backed rattlesnake, both abundant and wide-ranging in the state. Although copperheads accounted for 22 percent of the bites reported by Parrish, they caused no fatalities, whereas the western diamondback, which was blamed for nearly all of the bites included in the rattlesnake category (47 percent of the bite total), was responsible for some human deaths. The cottonmouth ranked next in order of frequency but inflicted only 7 percent of the bites.
Reducing the risk of snakebite is largely a matter of learning to recognize the dangerous species in your part of the state, becoming familiar with their habits, and observing some commonsense safety practices, a few of which are listed here:
- The first rule should be, never handle a venomous snake unless you are qualified by training or experience to do so. This admonition, while it may seem self-evident, deserves emphasis, for an ever-increasing number of snakebites are being inflicted on inexperienced amateur herpetologists and reckless adventurers. Other bites are the result of mistaken identification. In one such incident, a Houston radio announcer encountered a coral snake on a city jogging trail. Believing the snake to be a harmless species, he picked it up and was promptly bitten on the hand, whereupon, momentarily startled by the reptile's reaction, he quickly dropped it to the ground. Still not convinced that the snake was dangerous, he handled it a second time and was bitten again. Also to be carefully avoided is a dead venomous snake, for such a creature often can bite reflexively for periods lasting up to an hour after death, as can its decapitated head, a reaction Klauber (1956) elicited many times from experimentally beheaded rattlesnakes. One of the most sobering examples of such an accident is the case reported by Kitchens and his colleagues (1987) in which a Florida man died after having been bitten by the severed head of a large canebrake rattlesnake.
- Since nearly all snakebites occur on the arms or legs of human victims, avoid placing your hands in places where you cannot see, and wear protective footwear on the lower half of your legs when venturing into areas known to harbor venomous snakes. Be particularly alert when climbing rocky ledges or when walking near old logs and decaying tree stumps, places often favored by certain venomous species. It also makes sense when crossing a log to first step onto it in order to see what is behind it, then to step down on the other side when it appears safe to do so. Never reach into mammal burrows, especially in arid habitats where aboveground shelters are scarce, for such tunnels are frequently occupied by rattlesnakes. Since one of the leading causes of snakebite is the practice of lifting or turning surface objects with the bare hands, a sensible rule to follow is to move these items (rocks, boards, logs, brush, construction debris, etc.) with a long-handled tool such as a hoe, shovel, axe, or broomstick.
- To discourage snakes from maintaining permanent residence close to a home or vacation cottage, it is advisable to keep the premises free of debris. Rock piles, trash piles, stacked lumber, and various forms of junk not only provide the serpents with shelter but also often harbor the rats and mice that constitute the principal food of most venomous species. Removing such debris helps to eliminate the snake's cover and that of its rodent prey.
- If you must kill a venomous snake that is a threat to human safety, do so out of range of the snake's strike, which ordinarily is less than its own body length. To attack the reptile with a short-handled weapon such as a knife, hatchet or hammer is simply to invite an accident. Although this word of caution may seem too obvious to bear mentioning, it is clear from our review of Texas snakebite cases that accidents from this cause happen with some frequency.
For most people, snakebite is a terrifying experience that finds the victim both emotionally and intellectually unprepared to deal with such an emergency. Usually fear and extreme apprehension result from such an accident, when what is most needed at this time is a sense of calm. Despite the rarity of human death from envenomation in the United States, convincing a fearful snakebite victim that he or she has an excellent chance to recover from such a mishap is difficult. Nevertheless, every attempt should be made to convey this information to the victim, since to do so may relieve his or her anxiety and thereby expedite their recovery.
Reaching medical aid as quickly as possible should be the first objective, but with a minimum amount of physical exertion on the part of the victim, who, if alone and on foot, should not run. If the bite is on an extremity, immobilize the bitten limb or at least avoid moving it, since muscular activity hastens the spread of venom through the lymphatic channels. Moreover, when the bite is on a hand or arm, take off any rings and tight bracelets before swelling makes their removal difficult.
Other, more aggressive first-aid measures—including incision and suction, with or without a constricting band or tourniquet; application of cold to the bite site; compression wrapping of the extremity; or stun gun electroshock—may or may not be used, depending on the knowledge and decision of the victim. However, such procedures, some of which are potentially harmful, have not been embraced with equal enthusiasm among the best-informed medical specialists, although the same experts agree that the several preliminary steps mentioned earlier (reassurance, prompt transport to medical aid without undue exertion, immobilization of the bitten limb, and removal of rings and tight bracelets) are beneficial. One expert, Dr. D. L. Hardy (1992), reviewed several commonly recommended first-aid methods for North American pit viper bites and presented his evaluation of their effectiveness. Anyone with a serious interest in snakebite first aid is encouraged to read this article.
The following is an account of Texas poisonous snakes, their behavior prior to and during a bite, and the effects of the venom on the human body.
Texas coral snake
This seemingly inoffensive snake, which may not even attempt to bite if handled carefully, usually crawls away at the first sign of danger. It should never be touched, however, for an aroused specimen becomes unpredictable, and considering the high lethal toxicity of its venom, this serpent is potentially very dangerous to humans. Sometimes merely holding the snake gently causes it to turn its head, open its mouth, and without any apparent provocation, bite the hand that supports it. Some say that because the coral snake is unable to open its mouth widely, it can effectively bite only a highly curved surface of the human body such as a finger, toe, or the loose skin between these digits. That, unfortunately, is not the case. Just as a bit of epidermis can be pinched out with the fingers, so too can a coral snake gather up a fold of skin between its biting jaws, allowing its fangs to penetrate the skin. The serpent may use other defensive tactics as well. A coral snake that is approached too closely may lash out wildly at the oncoming target, though this is not considered typical Micrurus behavior.
The snake is far more likely to bite only when touched. Most coral snake bites occur when the snake is willfully handled, usually by someone who is attracted to the reptile's bright colors and, deceived by its small slender head, considers the snake harmless. The snake usually reacts to such familiarity by abruptly swinging its forebody sideways to seize the restraining hand. Then, seeming to sense that its biting apparatus is an imperfect one, the coral snake maintains its grip as long as it can, chewing on the hand to embed its short fangs as it tries to inject as much as possible of its meager venom supply. The minute, rigidly attached fangs, barely 1/8-inch long, are incapable of deep penetration, and the primary muscles responsible for the ejection of venom from the venom glands are not well developed in this species and are unable to drive the venom forcefully from the gland, down the fang canal, and into the victim.
Despite the snake's somewhat primitive method of venom delivery, its neurotoxically active venom is undoubtedly one of the most lethally potent of any U.S. serpent. The dose needed to kill a person of average stature is estimated by Minton and Minton (1969) at only 4 or 5 mg of dry weight, which, incidentally, represents nearly the entire pool of venom contained in the glands of most specimens 20 to 24 inches long. Larger snakes, of course, can be expected to deliver a greater quantity of venom. This was demonstrated by Fix and Minton (1976), whose studies of coral snake venom extraction, using the eastern coral snake as a model, yielded 20 mg or more from each of two especially large individuals measuring between 33 1/2 and 35 1/2 inches long. (Such large coral snakes are seldom encountered in Texas.) According to Russell and Puffer (1971), the venom is nearly 11 times as lethal as that of the copperhead, 5.26 times as toxic as that of the cottonmouth, and nearly 4 times as virulent as western diamond-backed rattler venom. Because of the coral snake's highly toxic venom, it is often said that a victim bitten by this species has little or no chance to survive the experience. On the contrary, and in spite of frequently quoted mortality figures ranging anywhere from 10 to 75 percent, few human fatalities result from such poisoning. In the first place, not every bite is accompanied by the injection of venom. Although Russell (1980) found 17 human deaths among 82 published reports of coral snake bites nationwide, he could find no record of a fatality from such an accident since Wyeth coral snake antivenin was first developed and made available back in 1967. It is of particular interest to note that we are unable to find even one authentic record of a human fatality from coral snake envenomation in Texas since 2 deaths were mentioned by True in 1883, more than 120 years ago. These cases, incidentally, are the first published records of coral snake bite fatalities for the United States and, at least until now, the last for Texas.
The severity of a coral snake bite is not easy to assess. Unlike the venoms of North American pit vipers, which typically cause severe local tissue damage and extensive hemorrhaging, that of the coral snake produces only minimal early signs of envenomation or none at all. Consequently, the victim often has no reason to believe he or she has been poisoned. Pain, if present, is usually minimal at first and confined to the area of the fang punctures. In a serious bite it may be moderate to severe, depending on the amount of venom delivered. The fang punctures, so small that they may scarcely bleed, are separated from each other by 1/4 to 3/8 of an inch; the presence of only scratch marks usually indicates an imperfect bite and the probability that no venom was injected. Swelling at the bite area is usually absent as well or, if present, is hardly noticeable. It is evident that the lack of conspicuous signs or symptoms soon after a bite belies the potentially serious consequences that may follow. Unfortunately, this can give the victim a false sense of security, resulting in his or her unwillingness to seek medical aid.
In most cases of coral snake poisoning the first alarming manifestations do not appear until several hours after the bite, at which time it may be too late to save a severely envenomed patient by the administration of appropriate snakebite serum. Prognostic symptoms, when they finally appear, include apprehension, giddiness and euphoria, thickening of speech, increased salivation, and tongue tremors. Nausea and vomiting may also occur, as well as pinpoint pupils, blurred vision, and drooping eyelids. The victim may later experience weakness, drowsiness, and a feeling of impending unconsciousness. In many respects the symptoms produced by coral snake poisoning are not much different from those observed in a seriously intoxicated person. In advanced cases of envenomation there is hypertension, and the pulse weakens and becomes irregular. Convulsions may also occur. This is followed by the sudden onset of facial and bulbar-center paralysis, after which limb paralysis occurs. Finally, death comes as a result of respiratory and cardiac failure. Fatalities generally occur when the snake has been given the opportunity to inject a lethal dose of venom, either by maintaining its grip for more than just a few seconds (most when they have hung on for longer than a minute) or by inflicting multiple bites.
Although most abundant in wilderness areas, the southern copperhead is frequently encountered in certain suburban parks and woodlots of our largest East Texas cities. In such places, where it can find shelter under brush and human-made debris such as boards, rock piles, roofing paper, and other construction rubble, it is generally the most abundant local venomous snake and the one responsible for the vast majority of human envenomations in and around the cities of Houston, Beaumont, and Port Arthur. In Harris County alone the number of people bitten each year by this snake and treated in local hospitals and clinics is probably between 20 and 30, yet we can find no record of a human fatality resulting from such injuries. This is no doubt a result of the copperhead venom's relatively low lethal toxicity compared with that of most other native venomous snakes, together with the modest quantity of venom carried in its venom glands. The total amount of venom contained in both glands of a copperhead is usually 40 to 70 mg of dry weight, according to Minton and Minton (1969), and the same authors estimate the minimum lethal dose required to kill an adult human at 100 or more milligrams. Another mitigating factor is the small size of the copperhead's fangs, each of which seldom measures more than 5/16 inch long, resulting in a shallow subcutaneous bite.
According to information assembled by Karant (in Wingert et al. 1980), only a single human death was discovered in his review of 2,000 cases of copperhead bite. He explained that this solitary fatality was probably not the direct result of copperhead poisoning but most likely was caused by certain side effects of envenomation that were never clearly defined. Despite these reassuring statistics, Amaral (1927) reported a human death from a copperhead bite involving a 14-year-old bitten on a finger. Likewise, P. Wilson (1908) recorded five deaths from copperhead envenomation, three of which he believed may have been exacerbated by the large amounts of whiskey consumed by the victims in their misguided attempts at treatment.
According to Sherman A. Minton, Jr. (pers. com.), who over the years has been involved as a physician with approximately 50 copperhead bite cases, generalized symptoms of envenomation by this species include local pain and swelling, nausea, vomiting, sweating, and thirst. In addition, the victims usually experience enlargement and tenderness of local lymph nodes, and the presence of blood- or serum-filled blisters is not unusual. In only one case, involving a five- or six-year-old girl, did he note hypotension and other evidence of shock. Minton commented that tissue necrosis can be severe but corrective skin grafting is rarely necessary.
Although the bite of a large broad-banded copperhead may cause serious medical consequences in humans, especially when the victim is a small child, records of human fatalities from copperhead envenomation are rare (even though the incidence of copperhead poisoning in Texas ranks second only to the number of snakebites inflicted on humans by the more wide-ranging western diamond-backed rattlesnake). Such a low mortality rate can be attributed to the snake's relatively short fangs, its modest venom supply (40-70 mg of dry weight per snake when extracted by milking, according the Minton and Minton ), and the comparatively low lethal toxicity of its venom.
Symptoms of poisoning by this species are generally not dramatic, consisting primarily of pain and swelling. A typical case history was reported by Fitch (1960), who, after being bitten on the middle finger of his right hand, carefully observed and recorded the signs and symptoms produced by the bite. Early manifestations included twitching muscles and a dull ache at the bite location, followed in about 10 minutes by noticeable swelling and discoloration in the same area. The pain, which at first was not severe, soon became intense as the swelling moved steadily up the hand; in a short time was followed by throbbing pain in the palm at the base of the middle finger and numbness of the skin. At this point, Fitch made a 1/2-inch incision through one of the fang punctures, the one that was the primary source of venom injection. (The other fang struck a knuckle joint and apparently delivered little or no venom.) Two hours after the bite, the swelling had reached 4 inches above the wrist and the throbbing pain was still present in the palm of the hand, at which time Fitch took a quarter-grain of codeine. Approximately 15 minutes later, when respiratory congestion became evident, he took an antihistamine in an effort to relieve the symptoms. By 10:15 PM the pain had reached its peak, prompting Fitch to take a second quarter-grain of codeine. Between 30 and 45 minutes later, the victim became nauseated and subsequently regurgitated, but he experienced no further deterioration in his condition after 12:45 AM. The systemic manifestations experienced earlier were gone by morning, although the affected hand eventually swelled to almost twice its usual size, and it was nearly a month before Fitch regained full use of his hand.
According to Parrish (1964), whose study provides the most recent survey of statewide snakebite statistics, only 7 percent of Texas' 461 hospitalizations for snake envenomation during 1958 and 1959 were caused by cottonmouths, despite the serpent's local abundance in many parts of southeastern Texas. The nationwide rate of approximately 10 percent was not much higher. Such a low incidence is not surprising, considering the snake's normally unaggressive behavior. Although very young cottonmouths often are quick to strike when approached, most adults of this subspecies we encountered in the field either tried to escape or simply pulled back their heads in a defensive stance without taking any aggressive action. Not only is the bite rate from this snake relatively low, but hospital records also show that few humans die from cottonmouth envenomation. Scarcely one human fatality a year can be attributed to this species nationwide.
Although not as lethally toxic as the venoms of most rattlesnake species, cottonmouth venom causes considerable local hemorrhaging, rupturing small blood vessels and allowing the blood to seep into the surrounding tissues, resulting in dark discoloration of the bite area and the oozing of bloody fluids from the injection site. Since the venom literally dissolves the affected tissues, the area at the site of the bite can become gangrenous, and in severe cases may even liquefy, complicating an already serious medical emergency. As evidence of the deleterious effects of cottonmouth venom, Allen and Swindell (1948) reported that in Florida approximately half of all bite victims suffered gangrene-crippled fingers or toes. In spite of the high incidence of tissue necrosis in such cases, Findlay Russell, one of the country's leading snakebite practitioners, believes this condition can be largely prevented by the prompt intravenous injection (by a physician) of adequate amounts of antivenin. Sherman A. Minton (pers. com.), another of the nation's eminent snakebite experts, takes a different view. Based on the results of animal experiments he conducted in the laboratory, together with clinical evidence, he found antivenin to be of little value in preventing necrosis from pit viper venoms. Other symptoms of cottonmouth envenomation may include pain in the bite area, swelling, weakness, giddiness, rapid or reduced pulse, drop in blood pressure, some breathing difficulty, and nausea and vomiting.
Western diamond-backed rattlesnake
Most of the more than 1,400 estimated (Parrish 1964) venomous snakebites inflicted each year on Texas residents are caused by this species, as are the majority of serious envenomations and most of the fatalities. Several factors, among them a great striking distance, long fangs, and a large venom capacity, account for the negative impact this snake has made on the state's human population. Other elements contributing to the diamondback's ranking as the most dangerous of all Texas serpents include the snake's continued abundance over much of its present range and its inclination to defend itself vigorously when disturbed. In spite of its ability to injure or kill a human victim, the western diamond-backed rattlesnake, like all other snakes, venomous or not, prefers to avoid confrontation with humans.
Its venom is not as lethally toxic as that of the rock rattlers, prairie rattlesnake, Mohave rattlesnake, or coral snake, although it stores a much greater quantity of the toxic substance in its venom glands than do any of the others. Using a variety of extraction methods, from manually squeezing the glands to stimulating them electrically, the maximum yield per adult is reported to range from 600 mg to 1,145 mg of dry weight, the larger amount having been removed from a specimen measuring 5 feet, 4 inches (163 cm) long. Klauber (1956) suggests that under ideal conditions as much as 1,500 mg could be extracted from a large western diamond-backed rattlesnake. He also gives 277 mg as an average extraction for this species.
It seems logical to conclude that because of the greater quantity of venom ordinarily delivered by a large rattlesnake, its bite would produce more serious consequences in a human victim than the smaller dose administered by a shorter rattler, all other factors being equal. This, however, is not always the case.
Theakston and Reid (1978), after hearing of a human seriously poisoned by one of three two-year-old western diamond-backed rattlesnakes he kept as pets, were motivated to investigate how so small a snake could produce such dire medical consequences in a grown human. In assaying the qualitative chemical changes in the venom of these specimens over time, the researchers demonstrated that the lethal toxicity of their venom was actually greatest when the specimens were only 2 months old, declining gradually until it leveled off after the snakes reached 13 months of age. A similar result, incidentally, was noted by Minton (1957), who tested the virulence of a single western diamond-backed rattlesnake's venom over a span of 19 years and concluded that its lethal toxicity decreased by 2.4 times during this period. Theakston and Reid also found that the venom of very young C. atrox, because of its defibrinating action, can cause serious internal bleeding in a human victim. As a result, they strongly urge clinicians to monitor carefully the blood-clotting quality of patients bitten by such a snake, since nonclotting blood in this case is a good indication that the offending rattlesnake is less than a year old and, more important, that the victim probably has been injected with a potentially fatal or near-fatal amount of venom. Minton and Weinstein (1986) likewise found a clear disparity between the lethal toxicity of juvenile western diamond-backed rattlesnake venom and that of the adults. Two specimens they examined from North Texas, each less than a year old, had venoms 6.6 times as toxic as that of adults from the same area. Variability in venom lethality was also evident among adult snake populations throughout the species' range; the most toxic samples were found in adult diamond-backed rattlesnakes collected in the Big Bend region of Texas, especially those from the base of the Rosillos Mountains.
In a typical case of poisoning by this species, the victim experiences a variety of signs and symptoms, some of which appear immediately, others much later. The first to be noted is pain in the bite area, usually intense. Occasionally pain is absent. More often, a serious case of envenomation produces agonizing pain, which begins at the site of the bite and over several hours gradually follows the course of the swelling. Swelling usually appears within 10 or 15 minutes and progresses along the bitten limb, toward the body. The more venom injected, the more severe the swelling. In particularly serious cases, swelling may even reach the body cavity, and the lymph nodes nearest the bite area may become tender and painful to the touch. A bruiselike discoloration also appears at the site of the bite soon after the venom enters the tissues; it ultimately may involve the entire bitten limb. In most instances the pulse rate increases (sometimes doubling), blood pressure drops, and frequently the victim experiences weakness, sweating, faintness, and dizziness. He or she may also suffer nausea and vomiting.
Death, if it occurs, is preceded by the following scenario, as described by Russell (1980): hemoglobin drops during the first 6 to 72 hours after the bite, abdominal bleeding occurs, as well as hemorrhaging in the heart, lungs, kidneys, adrenals, and perhaps also in the brain. Finally, the victim succumbs to acute pulmonary edema. It should be mentioned that unlike the dramatic, sudden-death snakebite episodes usually depicted in motion pictures and on television, human fatalities from pit viper envenomation generally do not occur immediately. They typically take place from 6 to 24 hours after the encounter. There are, of course, reports of victims succumbing to western diamond-backed rattlesnake bites in less than an hour, but they are uncommon and often involve small children whose lesser body weight places them at greater risk than adults.
Because the canebrake rattlesnake generally lives in areas remote from centers of human population, is not abundant in our state, and is often reluctant to strike at sources of passive annoyance, it is seldom the cause of human envenomation in Texas. Nevertheless, its bite can be deadly. Several fatalities caused by this subspecies have been reported for southeastern Texas, including one documented by Guidry that involved a small child bitten near La Belle in Jefferson County. This snake's danger is in its considerable striking range, its relatively long fangs, and its substantial venom output—Glenn and Straight (1982) obtained 244 mg dry weight from one specimen—to say nothing of the unusually toxic venom of certain populations. There is, of course, a certain degree of variation in the venom toxicity within a given snake population, just as there is in venom obtained from the same snake at different times in its life, although the elevated toxicity measured by Glenn and Straight is not the result of such normal variation.
The venom of juvenile canebrakes, like that of some other pit viper young, can actually be more toxic than that of the adults. This was discovered in a study by Minton (1967), who tested the venom of several canebrakes from the time they were five days old until they reached a year of age. Although the venom of the five-day-old snakes was not even one-third as potent for mice as that of adults, its toxicity gradually increased until at six months of age it had become nearly three times as potent. When the snakes reached one year of age, their venom toxicity had dropped to 1.8 times that of the adults.
Envenomation by this subspecies produces symptoms generally similar to those observed in many other pit viper bites. The canebrake's strongly hemolytic venom, like that of most rattlesnakes, causes pain, hemorrhaging, swelling, ecchymosis, vesiculations, weakness, faintness or dizziness, weak pulse, nausea, and even paralysis. Signs and symptoms manifested in a patient bitten by one of these snakes was reported by Parrish and Thompson (1958). The victim, a 37-year-old male reptile handler working in a large Florida tourist attraction, was struck at the base of the right index finger by only one fang. Even though the offending snake had been milked of its venom only 24 hours earlier, the man experienced a moderately serious level of poisoning. Within just a few minutes there was a burning pain at the site of the bite and the beginning of local swelling. Thirty minutes later the swelling had reached the back of the hand, and in 24 hours it extended almost to the man's shoulder. Other symptoms included cold and clammy skin, facial numbness, and a blood pressure reading of 100 systolic and 76 diastolic; four days after entering the hospital the patient was discharged and suffered no further complications.
Mottled rock rattlesnake
Although no human death has been attributed to rock rattlesnake venom, several reported bites by this species show that the snake is indeed dangerous to humans and probably capable of inflicting a fatal bite. Studies of banded rock rattlesnake venoms from several widely separated points in the snake's range have revealed the presence in some local populations of a dangerous component similar to Mohave toxin (in addition to the hemorrhagic elements found in most rattlesnake venoms) that produces neurological symptoms typically observed in victims of coral snake and some Mohave rattlesnake bites. Although such rock rattlesnakes have a distinct potential to cause a human fatality, the neurotoxic element responsible for their higher lethal toxicity has not yet been found in any Texas populations of C. lepidus. Nevertheless, the mottled rock rattlesnake has the capacity to cause serious consequences in humans, and a bite from one of these serpents should be treated at a medical facility with the utmost urgency.
In one of the few documented cases of envenomation by this subspecies, A. H. Wright, a renowned herpetologist of his time, reported that after having been bitten on the thumb by a specimen he was holding, he experienced considerable swelling of the affected arm, which also affected his lymph glands (Wright and Wright 1957).
Banded rock rattlesnake
Because this snake occupies rugged and usually inaccessible terrain, visited primarily by naturalists and a few adventurous backpackers, and since it is a timid creature that easily avoids large intruders, it is infrequently encountered in its mountain habitat and rarely bites humans. Such bites, when they do occur, nearly always happen to amateur or professional herpetologists who are deliberately handling live specimens at the time of the accident. We can find no record of a human fatality resulting from the bite of either this subspecies or the mottled rock rattlesnake, but there is good reason to believe that an accident involving a banded rock rattler could be life-threatening, at least when it involves certain isolated populations within the serpent's geographic range.
Although little is known about the precise biochemical nature of the snake's toxins, studies by Glenn and Straight (1982) reveal that significant variation occurs in the venom's lethal potency among several geographically isolated populations of this wide-ranging species. The biologists discovered, for example, that banded rock rattlesnakes from the Florida Mountains of New Mexico possess venom nearly 9 times more virulent than that of the same subspecies collected in Zacatecas, Mexico. Similar results were obtained by Rael and his coworkers (1992), whose experiments indicated the presence in the more lethal venoms of a neurotoxic component corresponding to the powerful Mohave toxin found in the venoms of some Mohave rattlesnakes. Using mice as laboratory animals, their studies revealed that the venoms of rock rattlesnakes from Chihuahua, Mexico, and some parts of Arizona and New Mexico had 3 to 100 times the lethal toxicity of those from Texas and were on average about 10 times as toxic as that of the western diamond-backed rattler.
Despite the high lethal toxicity of the more virulent venom samples, the individual dry-weight yield extracted mechanically from this species has typically ranged from only 5 to 33 mg. It may be assumed that the relatively small amount of venom ordinarily delivered in a single defensive strike is insufficient to kill a grown human. No doubt the severity of a bite would also be moderated by the smallness of the serpent's fangs, which are too short to penetrate the skin deeply. Scarcely 1/4 inch (5 mm) long in the adult, they are clearly better adapted for subduing lizard prey than for inflicting a lethal bite on a large mammal such as a human. Among other native pit vipers, only the western pygmy rattlesnake has fangs so small.
Unlike Mohave rattlesnake type A venom, which causes serious neurological consequences in humans but creates only minimal hemorrhagic effects, banded rock rattlesnake venom with Mohave-like component produces both significant neurological symptoms and equally severe hemorrhagic degradation. In at least two well-documented cases of human envenomation by the banded rock rattlesnake, the victims experienced considerable swelling of the bitten extremity and suffered two of the classic neurological symptoms of coral snake poisoning: labored breathing and impaired vision. Bitten on the hand by a banded rock rattler, Robert Hubbard (pers. com.), then a reptile keeper at the Houston Zoological Gardens, was admitted to a local hospital in shock 30 minutes after the bite. His hand and forearm were significantly swollen, and his systolic blood pressure was perilously low (70 mm Hg). He also experienced nausea, chills, vomiting, and severe pain at the bite area, but he eventually recovered. Another case, reported by Klauber (1956), involved an experienced herpetologist who was struck on the middle finger of his right hand by one fang of a 16-inch-long banded rock rattlesnake. The day after the accident, the swelling extended to the forearm, and the following day it reached the shoulder. A severe and burning pain, which began at the site of the bite on the second day, became nearly unbearable the next day, but then moderated, although five weeks after the accident some swelling persisted, accompanied by numbness and tingling.
Northern black-tailed rattlesnake
Because it is a relatively shy, retiring serpent with a penchant for remote and rugged terrain, the usually mild-mannered black-tailed rattlesnake rarely bites humans. A black-tailed rattlesnake's fangs are proportionately the longest of any native rattlesnake; those of a 4-foot (122 cm) specimen measured more than 1/2 inch (1.3 cm) along the curve, or about the same size as the fangs of a western diamond-backed rattlesnake a foot longer. Add to this the substantial amount of venom that the black-tailed rattlesnake's sizable venom glands are capable of producing, and it would seem logical to conclude that this is indeed a very dangerous snake. Yet that is not the case. In spite of the high venom yield produced by the adult of this subspecies—calculated by Klauber (1956) to average about 286 mg of dry weight per specimen), the lethal toxicity of the venom when injected into laboratory mice is less than that of most other Texas rattlesnakes, being only 79 percent as potent as the venom of the western diamond-backed rattlesnake. One reason for this is the venom's limited amount of chemical components responsible for severe tissue destruction. Because such components occur in higher percentages in timber, diamond-backed, and prairie rattlesnake venoms, bites from those species ordinarily produce more widespread damage, not only to muscles and subcutaneous tissue but also to various body organs. In recent times, the black-tailed rattlesnake has not caused a single human death, at least in Texas. Not since Amaral (1927) made the first serious effort to study the incidence of venomous snakebite in Texas do we find a documented case of human poisoning caused by this locally abundant pit viper. Russell (1960), on the other hand, reported four cases of black-tailed rattlesnake poisoning that occurred outside Texas, none of which resulted in severe tissue destruction. Hardy, Jeter, and Corrigan (1982) mentioned two instances of envenomation by this snake that did produce intense swelling and ecchymosis of the bitten extremities (perhaps because the offending rattlesnakes bit with such tenacity that they had to be forcibly removed), but they observed none of the severe tissue necrosis or hemorrhaging into vital organs that would be expected in serious poisoning by certain other Texas pit vipers. In the first case, the victim was bitten at the base of his left index finger by a 21-inch (53.3 cm) specimen, receiving only a single fang puncture; the other patient was bitten on the right wrist by a captive 33-inch (83.8 cm) black-tailed rattlesnake he was holding. Both victims fully recovered, suffering no local tissue destruction, hemorrhaging of blood into vital organs, or loss of limb or digit function.
The Mohave's most noteworthy attribute is its venom. Studies conducted over the last 30 years, according to Sherman Minton (pers. com.) show that in many individuals of this species the venom is the most toxic of any North American pit viper, even exceeding that of the eastern coral snake. When introduced into mice, and depending on the route of injection, it can be 10 to more than 50 times as lethal as that of the western diamond-backed rattlesnake. Containing a powerful neurotoxic element called Mohave toxin, it targets the victim's myoneural junctions and creates severe neurological degradation that can result in double vision and interfere with the normal functions of speaking and swallowing. It also affects the cardiovascular system, yet it is described as producing only minimal local effects on the tissues. Death, when it does occur, is the result of respiratory failure. Designated as type A venom by Glenn and Straight (1978), the highly dangerous venom containing Mohave toxin is present in C. s. scutulatus populations inhabiting southern California, southwestern Utah, southeastern Nevada, parts of western and southern Arizona, and the Big Bend region of Texas. The average venom yield from an adult specimen is reported by Minton and Minton (1969) as between 50 and 90 mg; the same authors estimated that it takes only 10 to 15 mg of the highly toxic substance to kill an adult human.
But not all Mohave rattlesnakes possess such deadly venom. Most of those occupying a wide geographic zone in south-central Arizona between Phoenix and Tucson contain a much less lethal form of venom, known as type B, which lacks the virulent nerve-damaging Mohave toxin. Unlike the A type, it produces dramatic local symptoms typical of pit viper poisoning, including considerable swelling, bleb formation, ecchymosis, and necrosis.
Because the Mohave rattlesnake, one of Texas' most dangerous serpents, is easily confused with the more common western diamond-backed rattlesnake, it is important for persons residing or traveling in the southwestern part of the state to make a careful distinction between the two. If the source of a snakebite is not accurately identified, the relatively mild local effects produced by the more lethal type A Mohave venom may cause an attending physician to underestimate the gravity of a bite. What may at first be diagnosed as a minor case may later prove to be a life-threatening condition, and when critical systemic manifestations finally appear, it may be too late for the successful administration of antivenin.
Fortunately, this snake is not particularly abundant in Texas, and its distribution is restricted to a relatively small part of the state. If it were even half as common as the western diamond-backed rattler and as widely distributed, the Mohave rattlesnake would represent an extremely serious outdoor hazard for Texans.
Overall, the prairie rattlesnake's venom is estimated to be from 2 to 2 1/2 times more toxic than that of the western diamond-backed rattler, although the storage capacity of the snake's venom glands is only about one-ninth that of its larger cousin.
According to Russell, Gans, and Minton (1978), the first and most frequently reported symptoms of C. viridis poisoning are pain and swelling at the site of the bite, which typically occur immediately following the accident but may be delayed up to half an hour. An early symptom of most North American rattlesnake bites, such pain ordinarily is less severe in this species than in bites by the diamondback. Russell (1960) treated two exceptional cases of poisoning by the northern Pacific rattler (C. oreganus), in which the patients described the degree of pain as minor. Envenomation by the prairie rattlesnake and its close relatives frequently results in a tingling sensation involving the tongue, mouth and scalp and occasionally the ends of the fingers and toes as well, symptoms not usually evident following the bites of other Texas pit vipers. Additional signs and symptoms include weakness, giddiness, sweating, faintness, and nausea; in severe cases the victim may experience a weak though rapid pulse, a drop in systemic arterial pressure, respiratory difficulties, and some degree of paralysis. According to Russell, death, when it does occur in humans, results from cardiovascular failure caused by a lethal peptide component in the snake's venom.
Since neither the snake's venom yield nor lethal toxicity have been studied, and there are no recorded case histories of bites by this subspecies, we know little about the effects of desert massasauga envenomation in humans. Like its close relatives the eastern and western massasaugas, it probably has a highly toxic venom containing a potent neurotoxic component, although this is not certain. If future research reveals that the desert massasauga does indeed possess such a venom, then its bite should be regarded as potentially life-threatening to humans. Even then, the snake's relatively short fangs and modest venom supply make death from a bite unlikely, for this is the smallest of the three massasauga subspecies. Besides, it has a spotty distribution, making an encounter with one of these elusive little rattlesnakes highly improbable. See also the western massasauga account.
Endowed with a relatively toxic venom believed to contain some neurotoxic components, the western massasauga can seriously poison a human victim, but its bite rarely causes death in humans. This is partly the result of the snake's relatively short fangs (barely a 1/4 inch long in the largest specimens) and its conservative venom supply. According to Minton and Minton (1969), the venom averages 25 to 35 mg by dry weight in an adult snake, and they estimate the lethal human dose at 30 to 40 mg. Since rattlesnakes rarely exhaust their venom in one strike, it is unlikely that a massasauga will inject a lethal dose in just a single stab of its fangs.
Symptoms typically associated with massasauga poisoning include immediate, often severe pain at the bite area; some swelling at the site, though usually not extensive; discoloration; a moderate degree of ecchymosis; faintness; and nausea. According to Russell (1980), none of the seven victims of Sistrurus poisoning he treated showed any significant changes in their blood picture, and all recovered uneventfully in just a few days. This does not mean that a massasauga bite should be treated as a trivial event. On the contrary, every bite by this species, if it produces signs and symptoms of poisoning, should be seen promptly by a physician experienced in the treatment of such a medical emergency. The lethal toxicity of western massasauga venom has not yet been established, although Glenn and Straight (1982) report that for the closely related eastern race, it is greater than for the majority of other rattlesnakes.
Western pygmy rattlesnake
Over the last 35 years, in the Houston area alone, five persons have been bitten by western pygmy rattlesnakes that each intentionally handled in the belief that it was a harmless juvenile hog-nosed snake.
Even this short-tempered little rattlesnake usually crawls away from danger if permitted to do so, but if provoked, even slightly, it is apt to launch a strike with the suddenness of a coiled spring. Its striking distance is limited, however, seldom spanning more than 4 or 5 inches (10-13 cm), and its fangs (measuring only 1/8- to 3/16 inch long) are not capable of deep penetration. According to Russell (1980), the lethal potency of pygmy rattlesnake venom when administered intravenously in mice is less than that of most other Texas rattlesnake species tested. It is also evident that although the larger eastern races of S. miliarius (nearly as big as a full-grown western massasauga) produce venom quantities averaging about 30 mg of dry weight per individual, the glands of the average western pygmy rattler must contain significantly less venom (apparently the amount has not been measured). Snakebite statistics reveal that the western pygmy rattlesnake is responsible for relatively few human snakebites, and a bite from this subspecies, though capable of producing serious medical consequences in humans, rarely if ever causes human death. We can find no record of a human fatality from its bite. According to Vick (1971), envenomation usually produces moderate to somewhat severe local symptoms and, in some of the more aggravated cases, may even result in marked systemic consequences such as hemorrhaging, passing of bloody urine, and breathing difficulty. Although most victims suffer pain, swelling (generally not severe), and some nausea, seldom do they experience significant tissue degeneration, nor is there a dramatic change in their blood picture. Unless the patient is a small child or a debilitated older person (which adds to the gravity of any envenomation), most victims recover completely and uneventfully in just a few days.