snakes

The two-headed monsters of myth may have a basis in reality. Two-headed snakes are rare but not unheard of, and one recently found in Spain is giving scientists an opportunity to study how the anomaly affects their ability to hunt and mate. "We hear of one every several years," said Gordon Burghardt, a herpetologist at the University of Tennessee who has studied several two-headed snakes.

The snake in Spain, discovered near the village of Pinoso, is a two-month-old non-venomous ladder snake Elaphe scalaris. It is about eight inches (20 centimeters) long. It's probably lucky it was captured—its chances of surviving in the wild are nil, said Burghardt. "Just watching them feed, often fighting over which head will swallow the prey, shows that feeding takes a good deal of time, during which they would be highly vulnerable to predators," said Burghardt. "They also have a great deal of difficulty deciding which direction to go, and if they had to respond to an attack quickly they would just not be capable of it." And that's assuming that both heads are hungry at the same time, and both are interested in pursuing the same prey. "Having two heads would be a hindrance in the wild," agreed James Badman of Arizona State University. "It would be much harder to catch prey." Arizona State was home to a two-headed king snake that was found as a baby. It lived for nearly 17 years in captivity at the university. Even in captivity, there are problems. Snakes operate a good deal by smell, and if one head catches the scent of prey on the other's head, it will attack and try to swallow the second head. On the whole, though, they can do quite well in captivity, said Burghardt. Thelma and Louise, a two-headed corn snake at the San Diego Zoo that's now deceased, had 15 normal babies. Anomaly, Not Evolution Two-headed snakes typically occur in the same way that Siamese twins do. A developing embryo begins to split into identical twins but then stops part way, leaving the twins joined. Among humans, 75 percent of conjoined twins are stillborn or die within 24 hours. "Cobra! Cobra!" A woman's screams pierce the hot night in a tiny village in Myanmar, formerly Burma. An American snake expert--the first scientist ever to survey all reptiles in this isolated region--happens to be in the village in his quest for new cobra species. He races toward the cries, tailed by a throng of curious villagers. Inside a hut, the woman's family stands rooted in fear. Coiled near the back wall, a 3-foot-long cobra arches with a hiss, poised to strike. Stealthily, the American approaches the hissing creature. With a few awkward thrusts of a "grab stick"--an aluminum pole with two 6-inch fingers or tongs--he grasps at the lightning-fast, poisonous animal, and snags it. Elated villagers crowd around to shake the hand of herpetologist (snake and reptile scientist) Joe Slowinski. Now the cobra hunter has good reason to be excited. The snake he's nabbed turns out to be an unidentified species--a spitting cobra that only inhabits the arid terrain of central Myanmar. Named the "Burmese spitting cobra" (Naja mandalayensis), it's the first new cobra species to be discovered since 1922. Surprisingly, cobras are usually shy and nonaggressive--deadly only when threatened or hunting prey. "Ever since I was a kid, I've loved snakes," Slowinski says. "I got bit by a rattlesnake when I was 15, and that didn't stop me." What is it about snakes that mesmerize us? For thousands of years, these slithery creatures have inspired religious myths, fanatical fear, and endless curiosity. Streamlined to the bare essentials--mouth, belly, brain, spine--snakes manage to slink over desert sands and rocky slopes as well as swim in rivers and glide through the rainforest canopy. In more than 100 million years on Earth, they've evolved to elegant perfection

. "The way a snake moves, through sleek body curves, light shining off its scales, is one of the most impressive sights nature has to offer," says cobra expert Wolfgang Wuster at the University of Wales, who collaborated with Slowinski in naming the new cobra. PERFECT BODY Apes climb with powerful anus and hands; frogs swim with webbed feet; falcons seize prey with sharp talons. Snakes--merely with a backbone--do all these things. Sheathed in smooth or rough scales, a snake's limbless body contains a long string of 100 to 600 vertebrae (backbones), which provide spectacular flexibility without sacrificing strength. Each vertebra features a pair of ribs that curve and attach to the inner surface of a broad scale on a snake's under-belly. Essential for snaky locomotion, these belly-side scales run crosswise like bulldozer tread; a snake's skeleton and belly scales are linked by muscles in complex overlapping layers, letting snakes crawl, climb, zigzag, caterpillar creep, coil, and crush. Cruising roads at nightfall is one way Slowinski sleuths cobras, since the species he's after tend to be nocturnal, or active at night. Cobras are nocturnal because the rodents they love to eat scurry around at night; also, cobras can overheat and die in intense tropical sunlight. Since snakes are cold-blooded, or ectothermic, external sources--sunlight, air, water, or warm blacktop roads--heat their bodies. When snakes need to conserve heat, they coil into a compact mass. Some scientists think snakes bask on warm blacktops after they've eaten to heat their bodies and speed up the digestive process. DEADLY VENOM One night in rural Myanmar, Slowinski came upon a spitting cobra lying on a road. As he moved to bag the snake, the cobra reared, hissed, and spit at him. Wearing protective glasses, Slowinski didn't back off. With his grab stick he snatched the snake behind its head and wrangled it into his cloth sack, trying to avoid a vicious bite. But he miscalculated: "Suddenly it bit me right through the bag!" The fang sank into his finger, and Slowinski sat down and waited for the pain--which never came. "I got lucky. The bite was dry." In other words, the snake released no venom, a poisonous saliva used to kill prey. If the cobra had injected venom, Slowinski's finger would have swelled within minutes. His muscles would have weakened and his eyelids drooped; he would have drooled and slurred his speech. Breathing would have become laborious--then impossible. In 12 to 24 hours, he could have died. "But the last thing cobras want to do is waste venom on animals they can't swallow whole, like people," Slowinski says. Snake venom is produced by special cells in two large venom glands on each side of the head. Out of 3,000 known species of snakes, more than 500 are venomous. The 10 most lethal snakes in the world belong to the elapids--often called the cobra family. Cobra venom kills via neurotoxins, proteins that paralyze an animal's nervous system and diaphragm, abdominal muscles used to breathe. The snake metes out the exact amount of venom needed to suffocate the prey, then swallows its catch. Headfirst. SNAKE SNACKS Small animals--frogs, birds, rodents, and snakes (even other cobras!)--whet a hungry cobra's appetite. Cobras track prey using senses of smell, sight, and hearing. As the snake hunts, its forked tongue flicks in and out through a notch in the upper lip; odor particles from the air and ground stick to the extended tongue. Inside the mouth, the tongue transfers scent particles to the Jacobson's organ, two pits on the mouth roof; the organ sends complex signals to the brain, which analyzes the scent chemicals.