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Posted by W von Papineäu on December 16, 2002 at 07:16:51:
NATIONAL POST (Toronto) 16 December 02 The sweet side of serpents: Herpetologists find that snakes have a difficult time expressing how much they know (Natalie Angier, New York Times)
Around the world, people dream of snakes more than they dream of any other animal. As scientists learn more about the biology, evolution and behaviour of these earthiest and most Freudianized of creatures, snakes just keep getting cooler, a fitting fate for a cold-blooded reptile.
Lately, biologists have been particularly mesmerized by the large, ancient and wildly diverse group of snakes called the vipers, a family that includes rattlesnakes, coral snakes and black mambas and more than 200 other species dispersed across every continent, save Australia.
Many New World vipers have elaborate rattles, a posterior shingling of fingernail-like plates that can shake a warning at 50 beats a second.
All vipers, however, are equipped with their signature erectile fangs, a cleverly designed set of dagger-like venom-delivery devices that lie flat against the snake's upper palate when the mouth is closed, but that pop out to unexpectedly nightmarish dimensions when the snake is poised to strike.
The vigour of the viper calling is shown in Biology of the Vipers, a generously illustrated volume being published by Eagle Mountain Publishing.
In it, several dozen herpetologists offer an array of surprising, amusing and cautionary findings about their snakes.
They discuss vipers that seem to recognize their kin and seek out their siblings preferentially when it is time to den down and curl up for the winter; and of mothers that are anything but cold-hearted.
Harry W. Greene of Cornell University and his co-workers describe cases of parental behavior among black-tailed and pygmy rattlesnakes. "We'd expected that after giving birth the mothers would crawl one way and the babies another," Greene said." But instead, we'd find a mother basking with her young day after day or guarding the entrance to a burrow while the babies were inside."
Once, he said, he saw a little viper start to emerge from its hole, apparently against its mother's better judgment. "She put her head on him and nudged him back inside." The researchers propose that parental behaviour has evolved among some vipers, together with delayed skin shedding. While most baby snakes shed their skins as soon as they are born, viper newborns, which are comparatively larger, do not discard their birthday suits until they are about 10 days old. While they are shedding that skin, their eyes are beclouded, they are susceptible to water loss, and they are extremely vulnerable. Hence the need for a mother's watchful care.
Though snakes have long been viewed as little more than pre-programmed pinheads -- "pretty low on the totem pole in intelligence," as one herpetologist put it -- Randall S. Reiserer of Vanderbilt University in Nashville, Tenn., tenders evidence that vipers can in fact learn from experience and fine-tune their hunting strategies to suit new circumstances.
He took 10 young massasauga vipers into his laboratory, some from swampy regions of the Eastern United States and others from the Arizona deserts. As a rule, Eastern massasaugas lure fast-moving frogs by giving undulatory wiggles of their tail, which resembles a worm. But when they see a slower-moving lizard, they do not risk a tail nip and instead pursue on their bellies. Western massasaugas, by contrast, are faced with fast-darting desert lizards. So they use their tails as lures, while they ignore the few frogs in the area as too toxic.
Reiserer showed that despite their different origins Western vipers could learn to hunt like Easterners, with tail wagging for frogs and pouncing on slow lizards, and Easterners could be trained to wag for lizards and eschew frogs.
"Snakes turn out to be very complicated creatures," he said. "But they have few ways to express what they know. It's easy to underestimate a tube."
Snakes, as it happens, are sublimely inert, spending less than 5% of their lives in motion. For all their fearsome reputation, vipers do not bite unless they really have to.
Three-quarters of the rattlesnake bites in the United States are described by herpetologists as "illegitimate," a result, according to Erika Nowak of the Southwest Biological Science Center of the U.S. Geological Survey, "of people who knew what they were doing, who knew that they were dealing with a rattlesnake but just kept poking it or picking it up or bothering it repeatedly."
Nowak, whose centre is in Flagstaff, Ariz., labours mightily to persuade people that having a rattlesnake in the neighbourhood is not a menace.
Rattlesnakes go to great lengths to avoid biting people or having anything to do with them at all. Even stepping on a rattlesnake is usually a non-event, and most people have no idea when they have done it, she said.
Nowak strives to improve the rattlesnake's image to limit the number of people who call the authorities and demand that a "nuisance" snake in their vicinity be moved elsewhere. Her research has shown that moving snakes far from their homes almost never works. Much of the time, the snakes die as a result.
In other cases, they simply return, travelling many kilometres over a period of months or years, until they find their way home, where all they want to be is left alone.
