The Big Squeeze
WE ARE SLOGGING through muck up to our knees, hoping to step on anacondas. Jesús Rivas, barefooted and only a little crazier than most field biologists, offers tips for detection. “You can tell by the way the mud bounces,” he says. “Or sometimes you’ll feel the snake move. If you have any doubt, the best thing is to reach down and see if you feel scales.” Something in my face makes him add, “It won’t bite unless you grab it too near the head, and these are big snakes, so chances are that won’t happen.”
Rivas considers this playing it safe. “I used to put my arm in the water and let the snake bite me,” he continues, “because then I knew where the head was and it was easier to catch.” Now he uses that method only as last resort. For instance, he got chomped the previous day when he offered himself as bait to stop a snake fleeing toward some thorns. “I figure a bite isn’t as bad as losing a snake,” he explains, which pretty much sums the man up. Maria Muñoz sighs and chuckles. Rivas’s quieter and more sensible (relatively) research partner, she is a petite woman who seizes anacondas while wearing lipstick and pearl earrings. “If you reach down and feel big scales,” says Rivas, continuing his lesson, “it’s a caiman, but we’ve stepped on hundreds of them and never been bitten.”
Rivas and Muñoz are conducting the first field study ever done on anacondas (Eunectes murinus), a member of the non-poisonous boa family and the largest snake in the world. The two scientists are Venezuelans and doctoral candidates, he at the University of Tennesee in the U. S., she at Universidad de Simón Bolívar in Caracas. The project is funded by PROFAUNA (the Venezuelan Wildlife Department), CITES, and the Wildlife Conservation Society.
Rivas and Muñoz have been pursuing anacondas on a 52,600-hectare ranch called El Cedral, near the town of Mantecal in the Venezuelan llanos, a vast savanna in the Orinoco River basin. During wet season, from May through September, the llanos become a shallow inland sea. In the dry season, as the receding water concentrates in low spots, so do the anacondas, making them a bit easier to find.
In nine dry seasons, Rivas, Muñoz, and occasional volunteers like myself have pulled more than 800 anacondas from the ditches, bogs, and streams of El Cedral. Despite the snake’s fearsome reputation, no one has come close to being eaten, crushed, or suffocated, though bites aren’t uncommon. Much of what Rivas and Muñoz are learning about the snakes’ diet, mobility, gender differences, and mating habits is new. The project is of more than scientific consequence. PROFAUNA will use Rivas and Muñoz’s findings to develop a management plan that may include commercial hunting of the snakes for their skins.
At the moment, trade in anacondas is prohibited in most South American countries where they occur. Guyana and Suriname periodically export live anacondas for zoos, research, and the pet market. The demand for pet anacondas is low, however, because they are so pugnacious and difficult to keep. Some skins get traded illegally, but everyone I spoke to—government and conservation officials in Venezuela and the U.S., people in the llanos, Rivas and Muñoz—agrees that the skin trade is not having a significant impact on anaconda populations, for reasons of both supply and demand. The snakes are hard to find and catch. Their large scales and dark subtle patterning are perfect camouflage in a muddy slough, but don’t translate well into flashy belts, shoes, and purses. Right now the main threats to the snake are habitat destruction and ranchers who routinely kill them on sight.
SOON AFTER photographer Gary Braasch and I arrive at El Cedral, Rivas and Muñoz take us into the field. The ranch is crisscrossed by a few raised dirt roads that run like plumb lines straight to the horizon. Our truck sends dozens of iguanas and capybaras scurrying. The roads are flanked by flooded channels crowded with ducks, wading birds, and more capybaras. Beyond these channels begins a vast patchwork of hyacinth bogs and grasslands cut by runnels. Everywhere, as far as the eye can travel, the savanna is dotted with thousands of water birds and still more capybaras, plus an occasional fox, caiman, and marsh deer. Cattle graze in the deep distance. Eco-tourists who stay in El Cedral’s small lodge like the ranch for its spectacular, conspicuous wildlife. So do anacondas, which eat it.
We disembark and wade across a waist-high channel to some hyacinth flats. Two biologists who are studying capybaras join us. Rivas and Muñoz had seen a large breeding ball near here earlier in the day, and have been waiting for reinforcements to help capture all the snakes at the orgy.
A breeding ball consists of anywhere from two to 12 males coiled around a female in a very impressive tangle. They will stay knotted for two to four weeks, nearly motionless, unless science or some other force interrupts the foreplay. It’s unclear why the courting period lasts so long. It’s also unclear how the males and females find each other. The prevailing theory is that the female lays down a pheromone trail as she crawls along, but Rivas and Muñoz have noticed that males following females tend to lick the air constantly, and that even though mating females barely move, the males still flock to them from all directions. Rivas thinks the female must emanate some sort of chemical signal that the males pick up through their tongues.
He also has noticed that when he shoves his hand into a breeding ball, the males use their powers of constriction to squeeze him out, so he surmises that the ball may be a slow-motion wrestling match to see who can maneuver into mating position with the female. But the female may have her own preferences, and since she is typically three to five times bigger than the males clinging to her, she may use her superior strength to deflect some suitors and select others.
“The idea is to disturb one male at a time and not disturb the female, so we make sure to catch them all,” instructs Rivas as we approach the ball, on the edge of a muddy channel. Seconds later he and the others are clutching big, writhing, unhappy anacondas. They try to grab the snakes just behind the head. Once caught, the snakes immediately coil around their captors’ arms or legs. I jump in to help with the unraveling and am soon enwrapped with anacondas. Their squeeze is emphatic but not painful. Rivas tells me, however, that it can be. “Even small males wrapped around a forearm can make my hand turn red, then purple, then go numb.”
Soon eight males are squirming in a big plastic drum. (One escaped, to Rivas’s chagrin.) The researchers let the female go free to attract more suitors.
The next morning we wade into the small Rio Guaratarito. The water is brown, the bottom muddy. “There are stingrays here,” says Rivas. “Drag your feet to kick them ahead of you.” We carry long poles to poke into shallow caves beneath the undercut banks. Anacondas like to relax in such places. For three hours we wade and poke, poke and wade, with no luck. Rivas thinks the snakes have been dislodged by rising water.
We spend the afternoon cataloguing snakes from yesterday’s breeding ball. Sitting on the concrete floor of his living room, Rivas reaches into an old fertilizer sack and pulls out a snake. He measures its head, then Muñoz slips an old sock over its face and wraps a few loops of electrical tape around it. The sock blinds the snake, calms it down, and decommissions its teeth.
When a snake refuses to lie still, Rivas holds it down with his legs while he measures its tail and spurs (small claw-like appendages on either side of the cloaca). Big snakes, 3.5 meters or more, require at least two people to manage. Muñoz records the date, hour, and location of the find. Using a razor knife, Rivas nicks away nine scales along one side of a spur and two along the other side, leaving an uneven white V. Then he removes seven scales on the snake’s other flank, thus assigning this particular anaconda the number 792. If it’s recaptured, this numerical tattoo will identify it. The second form of ID is the pattern of scales on the black-and-yellow underside of the lower tail--as unique to each snake as a human fingerprint. Muñoz records this on the data sheet. Then Rivas takes a blood sample, which he’ll analyze for its DNA.
The most time-consuming part of cataloguing snakes is measuring their length. Rivas or Muñoz, or sometimes a lucky visitor, attempts to hold the snake still while the other person runs a piece of twine along its spine. The snake at first makes a mockery of the process by stretching, contracting, writhing, and wrapping itself around the data-gatherers. Rivas and Muñoz’s solution is to take at least three measurements. The first one, when the snake is most agitated, can vary by 15 centimeters or more from the last one. The males from yesterday’s breeding ball are typical—two to three meters long, 3.75 to 7.5 kilos.
While trying to hold down a big male for measuring, I gag on a sudden noxious smell. “He musked you,” says Rivas. The musk emerges from glands near the cloaca. It’s the consistency of creamy lotion, usually toffee-colored but sometimes reddish. As an experiment, Rivas once put some musk on the floor and watched flies taste it; they died. He put some in a glass with fresh-water shrimp; they died, too. “The snakes probably use it to prevent ticks and leeches from attaching to the cloaca, one of their few parts that aren’t scaly,” he says.
The last snake is a breeding female caught the day before I arrived. “It’s Monica!” exclaims Rivas in happy recognition. Though most of the males get only a number, the scientists often name big females after female visitors or male visitors’ wives and girlfriends. (I last saw my wife Judith’s namesake, an ornery 4.8-meter beauty with a head as big as a man’s hand, slithering towards a couple of cormorants.) Rivas and Muñoz had caught Monica in ’92 and now have found her within 100 meters of the same place. Rivas fondly pats her massive flanks. She measures 3.5 meters now, half a meter longer than in 1992, and tips the scale at 21 kilos, a gain of 5.5.
Monica isn’t nearly as happy about this reunion as Rivas. While we’re putting her back in the sack, she nips one of my fingers. It bleeds some. “Now you are in the club,” says Rivas casually. It’s a discount membership, conferred by a nick, but I immediately begin devising a story for my two young boys: “The enormous beast clamped onto me, its fangs burning my flesh like a thousand needles, and as my blood drained I wondered whether I would ever escape this horrid death-grip and see you again, oh my children.”
But try as I might, I can’t crank my imagination up to the level of many earlier South American travelers: “A penetrating, foetid odour emanated from the snake, probably its breath, which is believed to have a stupefying effect, first attacking and later paralysing its prey. . . . To venture into the haunts of the anaconda is to flirt with death. . . . Their weird cries could be heard at night.” That’s British explorer Colonel Percy Fawcett writing earlier in this century.
Stories about gargantuan anacondas—15, 25, even 30 meters long—are common in South American chronicles. In his book Snakes in Fact and Fiction, James A. Oliver, former curator of reptiles at the New York Zoological Society, cites a Brazilian news story from 1948 about a 47-meter anaconda that fought a detachment of soldiers and knocked down buildings before being subdued. Oliver and others do credit an account from the 1940s of a snake 11.43 meters long, though some herpetologists doubt it. What’s certain is that anacondas longer than 6 meters are extremely rare. So far, the longest caught by Rivas and Muñoz was 5.33 meters long. The heaviest, a roly-poly 4.5 meters, weighed 80 kilos.
Yarns also abound about the snake’s hunting methods. In Tales of Giant Snakes: A Historical Natural History of Anacondas and Pythons, Robert W. Henderson, curator of herpetology at the Milwaukee Public Museum, and his co-author John C. Murphy, relate stories about anacondas sucking in prey from 50 feet away. The llaneros firmly believe that an anaconda can bite a bull on the nose, knot itself around a tree, and stretch to the thinness of a twig until the exhausted bull finally gives up and submits to being squeezed to death. They also believe that anacondas eat children.
“I’ve been told many times that when a man sees an anaconda, he must kill it,” says Rivas. “It’s almost a duty. If he sees one passing in a flood, he must curse it and throw stones at it or he will be cursed.” This fear and antipathy has meant death for many snakes, but also may have saved the anaconda from being heavily hunted. Rivas has never seen a llanero wearing anything made from anaconda skin: “They think anacondas are creepy and evil.”
But there have been some changes. “When we first came they would not tell us anything,” says Muñoz, “but now they all help us and tell us where they have seen snakes. They also know that tourism brings in money, and that tourists like to see anacondas.”
THE NEXT MORNING we head into the bogs with our poles again. The proper technique is stomp-poke-bounce, dubbed by Muñoz “the dance of the culebras [snakes].” It’s hot tedious work, and quiet except for the crunch of dry hyacinth leaves, the suck and slurp of the muck, and occasional wheezy barks from cabybaras or cries from southern lapwings. About an hour into the search Muñoz jabs an anaconda buried in the mud and calls me over so I can learn how it feels. But the snake has another lesson in mind, suddenly making a huge commotion in the brown water. “Qué grande!” shouts Muñoz, quite accurately. “Qué bonita!” she adds, more debatably.
It’s a female that turns out to be 3.65 meters long, 22 kilos. She strikes at us, giving a vivid demonstration of the anaconda’s ability to open its jaws 180 degrees and startle the bejesus out of a reporter. She’s an unpregnant female, just what Rivas and Muñoz want to implant with a transmitter. They learned how to tell pregnant snakes from unpregnant ones with the help of a local gynecologist, who did sonograms on some large females, to the distress of several women in the waiting room.
The next morning, using the drain board on the kitchen sink as an operating table, Rivas surgically implants a transmitter in the unpregnant female. A number of males and females will receive transmitters, each on a different frequency. Rivas will track the bugged snakes by boat, horseback, and foot to collect information on their dispersal during the wet season. A big female may drop 70 live babies (82 is the largest clutch on record) weighing 250 to 300 grams. Rivas will capture the pregnant females in mid-September before they give birth, then take blood samples from every baby. He will compare these samples with those of the males he caught wooing the mother. DNA analysis will tell him whether anaconda clutches are the result of single or multiple paternity.
The researchers have learned that pregnant females in the wild don’t eat for the entire six to eight months of gestation. They discovered this when they kept a pregnant female for observation and she seemed to be starving herself to death. The scientists worried, because pregnant anacondas in zoos do eat. Then one day the snake dropped her young, whereupon she immediately devoured seven ducks and chickens. Rivas ascribes the different behavior to different conditions. “To eat in the wild,” he says, “pregnant females would have to kill their prey, and that would mean risking their body with their babies in it.”
Herpetologists knew from captive anacondas that females are larger than males, but Rivas and Muñoz have found a radical size difference in the wild. (Males in captivity can reach 33.5 kilos—four times heavier than the largest wild males—probably because of overfeeding.) Rivas has some theories about the wide discrepancy, its advantages and disadvantages. Large females can prey on a bigger range of animals, have fewer predators, and, most importantly, can produce more babies. On the other hand, large predators need more food and suffer more injuries, because they tend to prey on bigger, more dangerous animals. It may be more sensible for males to stay small in the wild, thus requiring less food and incurring fewer risks. But if bigger males get to mate more, then size does carry an important advantage. Cross-referencing his data on each male with the DNA analysis of the clutches will give Rivas a partial answer.
Late one afternoon we find another breeding ball. When Rivas loses his grip on the female, she bites him. He growls but takes the opportunity to impart another lesson. “The first thing I learned about getting bitten was not to pull my hand away,” he tells me, “because then the teeth tear your flesh. It’s better to just let the snake bite and then grab the head. If it won’t let go, I push farther into the mouth. It’s counter-intuitive but it works, because the teeth curve back, so if you push farther in, it loosens the snake’s grip.” He grins. “They hate that. When they open up to get a bitter grip, you can usually pull your hand out the side.”
Now, to illustrate an anaconda’s dental structure, he holds out his freshly-bitten hand and points to a double half-oval of small red punctures. “This is from the upper jaw—here’s the outer row of teeth and here’s the inner row.” He turns his hand over. “And here’s the single row made by the lower jaw. You can see it’s not a bad wound. It’s like needles. I’d rather be bitten by an anaconda than a cocker spaniel.”
©Steve Kemper. All rights reserved. Cannot be reproduced without consent of the author.