IN one of the murky, hyacinth-choked pools in these vast savannas, whorls of thick spotted coils appear and disappear at the water's surface, hinting at the mass of snake hidden below. Three researchers tensely circle their submerged quarry when suddenly, cornered, the leviathan strikes, her dripping jaws shooting out of the water. Instantly they are upon her, grabbing head and tail, and she upon them, coils tightening around arms, legs, waists. For a moment it seems an even fight as the men, knotted in serpent, struggle even to remain upright. But eventually they manage to extract all 15 feet of her from the muddy lagoon. She is taken, the anaconda, the biggest snake in the world.
Here in these savannas, as elsewhere, the giant anaconda provokes both wonder and fear. Yet almost no scientific studies have been done that might dispel the colorful folklore of monstrous man-eating horned snakes that breathe poisonous gas and have the power to hypnotize human victims.
Now, in what researchers say is the first field study of the species, a team of American and Venezuelan biologists is providing a long-awaited glimpse into the life of this mysterious snake and beginning to sort anaconda fact from fiction.
"It's the only project of its kind in the world," said Dr. Robert Henderson, curator of herpetology at the Milwaukee Public Museum and co-author of the forthcoming book "Tales of Giant Snakes: A Historical Natural History of Anacondas and Pythons" (Krieger Publishing). "This is a wonderfully spectacular snake that's piqued the imagination of people for literally hundreds of years."
Researchers say that though poorly understood, the anaconda is far from untouched by humans, with thousands of skins traded each year, many illegally, for use in boots, belts and wallets. Biologists say the new work will help wildlife managers and conservationists to decide how the illegal trade might be replaced with a managed harvest aimed at conserving the species.Continue reading the main story
Almost nothing is known of anacondas' life in the wild. The snakes are secretive and often lie submerged in inaccessible rivers and lagoons. Biologists seeking to study anacondas must first catch them, one by one. No capture is routine: finding and subduing a single snake can easily require the determined efforts of three or four researchers.
The species, known as Eunectes murinus, ranges throughout South America's Orinoco and Amazon River basins. But Dr. John Thorbjarnarson, a conservation biologist at the Wildlife Conservation Society in New York, and his team chose to study the snakes here in the Venezuelan savannas, known as the llanos, at a ranch called Hato El Cedral.
"I'd kept hearing about this mythical place," said Dr. Thorbjarnarson who heads the joint effort of the Wildlife Conservation Society and Profauna, Venezuela's national wildlife department. "I'd heard these tales of El Cedral, that snakes were everywhere, hanging from the trees, that you had to push them out of the road."
A working cattle ranch, El Cedral is also a preserve rich enough in wildlife to attract a healthy ecotourism trade, particularly in the dry season. Its extensive savannas, navigable only by boat in the rainy season, turn in dry weather into a patchwork of isolated pools, where more than 500 snakes have been found and marked since the project began in 1992.
In tracking these snakes, biologists have got a first peek into the love life of anacondas. When it comes to anaconda sex, they have found, the more the merrier. In the breeding season, which has now begun in the llanos, a single female can be found entwined with as many as 12 much smaller males in a heaping mass known as a mating ball. Researchers say the females appear to hang out in a pool of water, draped in and visited by as many as 17 consorts for as long as four to six weeks.
"Talk about foreplay," said Jesus Rivas, an ecologist at the University of Tennessee in Knoxville who has carried out much of the field work along with Maria Munoz, an ecologist at Simon Bolivar University in Caracas, Venezuela.
The discovery of the mating balls raises numerous questions, including just which of the males fathers the snakes and what the snakes are doing in these heaps for so long. To begin to answer these questions, Mr. Rivas is extracting blood from females, males and newborns to determine paternity using DNA tests. Researchers are also implanting radiotransmitters in young snakes to learn their fate, which for many is probably to make a snack for a caiman, the alligator-like creature that throngs the murky waters.
Biologists have found that life is dangerous for the adult anacondas too, even though they are the top predators. For while the anacondas feed on relatively docile prey like ducks, some of their other meals can be quite dangerous. After subduing their victims in squeezing coils, asphyxiating and sometimes drowning them as well, anacondas typically swallow their prey head-first. Large females can eat giant rodents called capybara, which reach the size of a small dog, and even caimans and white-tailed deer. But it is not a simple matter to swallow a five-foot-long caiman or to fight off sharp-clawed capybara struggling to free a mate. The female anacondas often bear numerous scars as the price of lunch.
Some snakes' appetites outstrip their intellect. Dr. Thorbjarnarson said he once found a dead deer with anaconda teeth marks on its heavily antlered head: the snake had presumably tried again and again to swallow the buck headfirst until the antlers forced it to accept defeat. Dr. Thorbjarnarson said he had also heard of anacondas consuming deer from the rear only to discover at the end a pair of antlers too magnificent to swallow. One snake found by the biologists had sliced itself open by gulping down a turtle with razor sharp shell edges.
Another way of studying the anacondas' menu is by examination of the feces. Even a large capybara, after its transit through an anaconda, is reduced to little more than a few claws and some tufts of fur. With turtles there may be a bit of shell and with caiman perhaps some tell-tale scaly skin.
Anacondas are rumored to partake of humans as well. In the llanos when someone is missing, fingers are often pointed at the giant snake, but biologists say there is no real evidence so far that people are part of the anaconda diet.
For females, the half-year long pregnancy is also a tough experience. While pregnant, they eat little or nothing. Yet these fasting females, said Bill Holmstrom, another researcher on the project from the Wildlife Conservation Society, can give birth to as many as 78 or more baby snakes. After a birth, a female's weight can drop by nearly half.
Two of the biologists, Mr. Rivas and Ms. Munoz, decided to make a study of the gestating females. To make sure the snakes were indeed pregnant, they found they had to establish a kind of reptilian maternity ward, where they checked the waiting mothers with ultrasound.
Seeking to establish the range required by an anaconda, the biologists tagged the snakes with radiotransmitters. They found that during the dry season, the snakes roam a regular area to which they return each year. Researchers say males, the smaller of the sexes, and nonpregnant females seem to remain in a 50-acre area. On the other hand, pregnant females, often among the biggest and bulkiest of anacondas, barely move at all, content to keep within a mere third of an acre until the job is done, sunning their ever more hulking bodies on the water's banks.
The biologists here say they still do not know enough to judge whether anacondas can be harvested safely and profitably. In particular, because of the difficulty of taking an anaconda census, researchers are concerned that it might be easy to overharvest a population without even knowing it.
Dr. Gordon M. Burghardt, an evolutionary ethologist at the University of Tennessee in Knoxville, said the anaconda researchers had developed a handful of tricks of the trade that should be of great help to others beginning work on giant snakes. The subject of the researchers' most recent publication is the sock trick.
If a sock is pulled over an anaconda's head, it calms the snake, allowing researchers to transport it to their makeshift laboratory. But measuring even such a relaxed anaconda can be difficult. Researchers, after much experimentation, found the most reliable method was to trace the snake's long, coiled spine with a string, which is then measured.
When it comes to anacondas, questions of weight and length loom large. So far at Hato El Cedral, the heaviest snake has weighed in at 214 pounds and the longest at more than 17 1/2 feet.
While clearly the heaviest snake in the world, anacondas get competition from reticulated pythons when it comes to length. Reports of anacondas that are 60, even 150 feet long, have never been verified. Dr. Thorbjarnarson said the tallest of these tales was of a snake so long it took two days' march to get from one end to the other. He said the most frequently cited, and presumably reliable, report of an outsized anaconda is of a Colombian snake that was said to have measured 37 1/2 feet with a surveyor's tape. It subsequently escaped.
Even in the hands of biologists determined to take accurate readings, a snake that can tense and relax is hard to measure. The fear and boasting that such creatures inspire may also contribute to a general inflation in reported sizes.
So while scientific study has begun to replace legend, the anaconda still has not yielded its secrets to probe and calipers.
Sometime around 1910, Theodore Roosevelt offered a $1,000 reward to anyone presenting a live snake measuring 30 feet or more. Over the years the reward has been increased and the Wildlife Conservation Society's offer now stands at $50,000, a reward that to this day remains uncollected.
A picture caption in Science Times on Tuesday about anacondas in Venezuela carried an incorrect credit. The photographer was Maria Munoz.