The private lives of pit vipers

National Wildlife, August-Sept, 1995 by Michael Lipske

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-delance, "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 suffering from kidney disease.