The Private Lives of Pit Vipers
New research on rattlesnakes reveals how little we really know about venomous serpents
- Michael Lipske
- Apr 01, 1995
ON THIS WARM October afternoon in the craggy Chiricahua Mountains, Kevin Costner is sunning his body on a rock. Honest, right here in lovely southeastern Arizona!
On second thought, with the sun high and hot over the desert, the handsome devil may have crawled into the cool shade of an overhang. But he is up there in the thorny hell of Silver Creek Canyon, among the cholla cactus and cat's claw acacia, and biologist Harry W. Greene will find him. Cornering Costner- - a blacktail rattlesnake- - should be a cinch, half- an- hour's work, because the snake has a radio transmitter sewn into his abdomen and Greene has a radio receiver that picks up the transmitter signal.
To Greene, a biology professor at the University of California - Berkeley and a highly regarded authority on venomous serpents, all blacktail rattlesnakes are "very, very beautiful animals," their greenish- yellow bodies crossed by dark, irregular bands, their tails the color of charcoal. But one male blacktail is special. Identified for research purposes simply as Number 9, this serpent is, in Green's eyes, such a standout that the biologist nicknamed him after a movie star.
For the past six years, the 49- year- old herpetologist has tracked a total of 19 blacktails up and down the arid flanks of the Chiricahuas, from the limestone rimrock where rattlesnakes hibernate in crevices through the cold months, to the canyon bottom where they hunt for rodents and engage in sex lives both robust and strange.
Greene's goal is to build a detailed chronicle of the life of the blacktail rattlesnake, a species found from central Texas to western Arizona. Herpetologists can then compare that information to what is being learned about other venomous snakes of the fascinating and fearsome reptile clan known as pit vipers. Greene and other scientists estimate that of the world's roughly 145 pit viper species- - including 17 in the United States- - at least 80 are threatened with extinction. Greene believes pit vipers are more victimized than vicious and that the more he can learn and then teach people about these snakes, the more likely the rest of us will be to cut them some slack.
A group that includes the New World's rattlesnakes, pit vipers range from Asia's green tree vipers to North America's copperhead and Latin America's bushmaster, which is the world's largest, sometimes exceeding 10 feet in length. All share a characteristic as technologically sophisticated as Harry Greene's radio gear. This is the heat- detecting, concave organ on each side of a pit viper's head (between its eye and nostril) with which hunting serpents home in on warm- blooded prey. Greene hypothesizes that the infrared- sensitive facial cavities developed not as aids to feeding but as defensive organs originally used to sense the size of, and thus the potential threat posed by, various creatures the snakes encounter.
Group members also share a more notorious characteristic. Folded against the roof of a pit viper's mouth are two long, curved, hollow teeth. When a pit viper strikes, the two fangs flip forward and, like dual hypodermic needles, inject the modified saliva that is viper venom. Pity the viper's prey, which for blacktails is most commonly wood rats, rabbits and rock squirrels. Propelled rapidly into shock as its dying heartbeats pump poison through its system, the small animal at the same time is internally tenderized by digestive enzymes in the venom that go to work even before the snake gets down to eating. Digestion before ingestion, snake people say.
Aside from an inquiring mind, sturdy shoes and steady nerves, the main tool that Greene, 48, brings to his searches is radio telemetry- - the transmitters implanted in snakes and the antenna and receiver wielded by himself and his partner in blacktail tracking, David L. Hardy, Sr. A Tucson anesthesiologist who never lost his teenage passion for herpetology, Hardy, now 60, is also an expert on the effects and treatment of snakebite, comforting knowledge for the novice rattlesnake tracker accompanying the pair in the field.
Almost reverently, Greene calls the radio gear and what it accomplishes for him "the trick," the technologically enhanced ability to say "how do you do" to the same rattlesnake time and again- - sometimes hundreds of times again- - over the course of years. Part science, part orienteering, the technique has revolutionized his and other studies of these elusive animals. In this first detailed study of a blacktail population, Greene and Hardy have followed male snakes that crawled three yards a minute- - as much as a quarter mile a day- - in single- minded pursuit of breeding females. They have come across blacktails courting in trees (behavior hitherto unknown in rattlesnakes), and they have identified the snakes' favorite rocks and refuges for hibernating and for hanging out.
The search for Kevin Costner has gone on for 30 minutes now, the trackers climbing through what David Hardy calls "prickly terrain," the desert's heavy helping of cactus, shin- daggers and other evil- tempered plants. Greene calls this his favorite part of the United States. In Cochise County, in the neighborhood of the study area, he and Hardy can find seven other species of rattlesnakes- - plenty of grist for students of snakes and snakebites.
The researchers' beeping radio leads them to the handsome hunk of reptile. Loosely coiled in the shadows beneath a clump of manzanita and oak, Number 9 is just under 4 feet long (about maximum for a blacktail) and perhaps 12 to 15 years old. He is in what Greene calls a hunting coil, his wide head resting on the outermost loop of his body. A hint of a ravine leads downslope toward the rattlesnake, probably a game trail that can funnel a rabbit or rock squirrel within striking distance. A rattlesnake can wait in ambush for days.
Greene guesses that blacktails get by on about 10 meals a year. Dinners are few but, in relation to a snake's size, ample. "The biggest meal I've ever recorded for any snake in the world was for a pit viper that had a lizard in it weighing 156 percent of its body weight," says Greene. "That would be like me eating a 250- pound cheeseburger without even cutting it into pieces."
Greene and Hardy go about the business of recording Number 9's location and behavior on data sheets. Greene writes the snake's number and the date on a strip of orange surveyor's ribbon, then ties it to a nearby ocotillo branch. After six years, many orange ribbons dot the canyon.
Throughout the visit, Number 9 neither blinks (snakes have no eyelids) nor rattles his trademark tail. Nervous rattlesnakes, however, can buzz their tails for hours, the 60- cycles- per- second vibration of hornlike segments powered by specialized tail- shaker muscles structurally similar to heart muscle.
To collect recruits for their study, Greene and Hardy rely on chance encounters with blacktails in the field. During mating season, they track randy, radio- equipped males to find new female blacktails. When the duo locates a new snake, they anesthetize it, and Hardy surgically implants a half- ounce radio transmitter in the abdomen. Hardy and Greene have seen the snakes preying on rodents only days after surgery, evidence, they say, that the procedure does not slow down blacktails. Each battery lasts nearly two years.
Even a radio- equipped snake can be hard to find. Signals bounce confusingly off boulders and other obstructions. And the snakes blend so well with their surroundings that Greene has come close to standing on radio- marked snakes before he actually saw them. "A big part of being a snake is to be hard to see- - to not have to expose yourself and have a direct interaction with a predator," says Greene. Red- tailed hawks eat rattlesnakes, as might cougars, coyotes and coatimundis, all at home in the Chiricahuas.
When Greene and Hardy locate a marked snake- - finally picking out a telltale patch of color in the shadows beneath a cactus clump or under a rock edge- - they often do their observing from a respectful distance with binoculars. Surgeries aside, their aim is to disturb the serpents as little as possible.
The two have come to know blacktails as individuals and as a community. Repeated radio contacts show that male snake Number 3 resides in a particular slice of canyon, even down to favoring the same boulders to hide under from one year to the next. Blacktail Number 9 is equally loyal to his stretch of the canyon. Neither Number 3 nor Number 9 have been found entering each other's activity range. Yet other male blacktails bearing transmitters do turn up in the neighborhood of Numbers 3 and 9. Number 9 has even shared a hibernaculum, or winter den, with another male.
Years of work in the Chiricahua Mountains have provided Greene and Hardy with an opportunity to observe the male blacktail rattlesnake's single- minded dedication to sex. Female pit vipers, including blacktails, breed infrequently, perhaps once every three to five years. The energy requirements of egg production are too great a drain for annual breeding. So in any mating season, sexually receptive females are in short supply.
Blacktails breed in late summer. Males use their forked tongues to detect female scent trails, which they follow with the tenacity of bloodhounds. "I've had a couple of males crawl across my boots while they were chasing females," says Hardy. "If you stand still, you're just another object to them."
When the male rattlesnake at last finds the object of his devotion, mating may occur within hours or not for several days. During courtship, the male "rubs up and down the female's back," Greene says, "and tongue- flicks her and so on, and eventually it becomes more intense, and he attempts to raise her tail and insert one of his penises." Like lizards, male snakes have two penises (the bifurcated organ is called a hemipenes). Why two? "Nobody has a clue," says Greene.
From all this may come five to ten baby blacktails, liveborn the following summer and fully loaded with tiny fangs, venom and a button rattle.
Greene has worked with vipers in the field from Costa Rica to Uganda, yet has been nipped only once, by a copperhead he handled in high school. "I was holding the snake improperly, and it bit me in the thumb," he says of the single- fanged puncture, which required no medical attention.
Severe viper bites may cause massive swelling and internal bleeding in human victims. Bites may blister and blacken tissue and, as happens about a dozen times a year in the United States, may kill. The differences in result may reflect individual human sensitivity to venom or may stem from varying amounts of venom injected by striking snakes. A snake may bite without using its venom, or its poison may be in low supply if the snake has recently emptied its venom glands into an earlier target.
Many of the 8,000 people bitten by pit vipers on average in the United States every year were courting trouble. Greene's colleague, David Hardy, has studied who gets bitten and why. For 20 years, the physician has pored over Tucson, Arizona, bite records and has found that about two out of three snake bites are what he calls "illegitimate," meaning, "You've seen the snake, you know the danger, you're still going to interact with it, and you get bitten."
None of which means pit vipers do not stab their fangs into the ankles of innocent hikers or cause other human misery. Latin America's infamous fer- de- lance, "a rather unpredictable snake," as Harry Greene says, bites from 200 to 250 people a year in Costa Rica, killing 1 percent of its victims.
On the other hand, the deadly venom of the jararaca, a pit viper of Brazil and Argentina, contains the key to medical miracles. Researchers in the 1970s were able to synthesize a compound in the venom, using it to create captopril, a potent drug widely prescribed for treating high- blood pressure and heart failure and now worth $1.3 billion in annual sales for its manufacturer, Bristol- Myers Squibb. Last year, the Food and Drug Administration approved captopril as a tool for treating diabetics with kidney disease.
The jararaca is not an isolated case. An experimental drug derived from venom of Malayan pit vipers is undergoing trials for treatment of stroke victims. For humanity, pit vipers are turning out to be one of those bad- news/good- news packages. But people have been pretty much all bad news for the vipers. In America, colonial- era rattlesnake bees- - community hunts aimed at wiping out the reptiles- - have evolved into rattlesnake roundups like the one held every year in Sweetwater, Texas.
Put on by the Sweetwater Jaycees since the 1950s to raise money for local charities, the roundup draws as many as 35,000 spectators. Thousands of snakes, mostly western diamondbacks, are killed during a single March weekend in Sweetwater. The January 1991 issue of the journal Oryx estimates that all U.S. rattlesnake roundups- - they are held in several states- - may remove from the wild as many as a half- million snakes a year.
People kill pit vipers in other ways, too. For example, the timber rattlesnake appears on state lists of endangered or threatened wildlife throughout the Northeast. It has fallen victim to rural housing construction near its dens and to illegal collecting. In Vermont, only two known timber rattler populations survive. New Hampshire has just one. In Maine and Rhode Island, the species has been extirpated.
Throughout the world, no more than a dozen pit viper species receive special protection, says Greene. Some species are particularly vulnerable because they occupy small ranges on islands or on isolated mountains. Many of these, he fears, are in danger of extinction.
Greene's blacktail rattlesnakes are a happy exception- - their populations robust, their prospects in the Chiricahuas good. Another place where pit vipers crawl with confidence is the floor of Greene's laboratory classroom.
Every spring, he has his students sit on their lab tables while he releases a western rattlesnake onto the floor. He found it years ago resting on the wall of a Berkeley day- care center. "It crawls, it doesn't get excited, it's a very mellow animal," he says of his rattlesnake's classroom demeanor. While the serpent slithers hither and thither, Greene lectures calmly about myths people have attached to pit vipers and about the snakes' splendid adaptations.
Harry Greene calls this teaching approach "leading people to the snake." He also says that by the time his pet has been returned to its cage, more than a few students seem to have made the long mental leap toward meeting a potentially dangerous, always mysterious, and perhaps ultimately unknowable other being halfway.
Writer Michael Lipske traveled to Arizona to meet with snake biologists and with the snakes themselves.