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Males have paired sex organs--each called a hemipenis, or half penis--hidden in the base of the tail. Some species, such as common king snakes, deploy these alternatively in successive matings--perhaps, says Greene, to allow more frequent copulation. When Borneo's yellow-lipped sea- kraits breed, as many as half a dozen males may pile on a lone female. Copulation is usually brief but can last more than a day for Western diamondbacks (probably to reduce the female's exposure to rival males). Female snakes too deploy cunning reproductive strategies. North American pit vipers, for example, store sperm for months, until some instinct tells the cold-blooded creatures that the temperature is right for fertilization. Like birds (close kin), most species are egg layers, though some give birth to fully formed young.
The hatchlings of some species exhibit survival strategies that might seem beyond their tiny reptilian brains. Young Eastern hog-nosed snakes, for example, feign death if they sense a threat. Are they consciously aware of danger? Or, as Greene puts it, "Does a mere serpent have reflections and intentions?" To learn more about snake behavior, Greene and his colleagues are going to plant tiny radio beepers inside newborn rattlesnakes. Says he: "Radio telemetry allows us to wonder more accurately what it's like to be a snake."
Most astonishing to Greene are snakes' keen senses--of smell, temperature and touch--which make up for their lack of external ears and limited vision (except for night snakes, which have catlike eyes). That flickering forked tongue, for example, loathsome as it may seem, actually gives the snake the chemical equivalent of stereoscopic vision; by responding to the relative number of odors on either side of the tongue, the snake can pinpoint potential prey, mates or enemies. Pit vipers, for their part, are equipped with keen infrared sensors near their nostrils, so even if blinded, they can strike a mouse several feet away simply by detecting its body heat.
Greene, who wrote his book in response to a challenge from the late writer Norman Maclean (A River Runs Through It)--"Look, just tell me why you work with those damned old rattlesnakes," Maclean said--makes no excuses for them. Snakes kill more than 20,000 humans a year, he admits, mostly farmers in the tropics who are accidentally bitten by vipers, although boots and antivenom have reduced the toll in recent years. In the U.S., where 1,000 to 2,000 snakebites occur annually, mostly by rattlesnakes and copperheads, fewer than 10 result in death. The majority of victims, says Greene, who has been nailed only once ("not seriously" by a copperhead as a teen), are "macho types"--young men who handle venomous snakes carelessly. "Snakes are more afraid of us than we are of them," he insists. "They'll only bite if they perceive a threat." Of course, you'd expect to hear that from an ophidiophilic scientist whose E-mail handle is crotalus, the genus name for rattlers.