The green anaconda is custom-made for this ecosystem, says Rivas.
The anaconda's eyes and nostrils are on the top of its head so it can breathe and see its prey while submerged under water. To find his quarry, Rivas roams the llanos in his bare feet, alternately wading and doing a modified breast stroke.
The anaconda, which is a water snake, typically grows to about 20 feet (6 meters) long, weighs several hundred pounds, and can measure more than 12 inches (30 centimeters) in diameter. The females are larger than the males.
Although anacondas might eat only once or twice a year, they eat their prey live, head first. And because their jaws unhinge, the snakes can eat prey much larger than they are.
In the "Shoes" of the Snake
Although green anacondas have a reputation as man-killers, they rarely attack humans, according to Rivas.
The anaconda kills with power, not poison, and capturing one requires at least two people and a lot of technique.
"The big thing to prevent is what we call the 'evil loop,'" says Rivas. "The snake is all muscle, and if it gets to make a loop around the prey, it's all over."
Anacondas bite, and over the years Rivas has been bitten innumerable times.
He has devised a low-tech approach to make it easier to collect dataputting a sock and duct tape over the snake's head to slow it down. "The snakes' first priority is to protect themselves, and the head is the most vulnerable," he says.
Rivas is one of a growing number of biologists and naturalists who advocate looking at animals from an animal-centered perspective rather than anthropomorphically (attributing human characteristics to them).
"Animals live in a whole world of smells and sounds and perceptions of their environment that we're not even aware of," says Rivas. "We see a snake lying in the sun for hours on endnot moving, doing nothingand based on our own experience, we would conclude that it is doing nothing. But if an alien species was to look down at us, sitting at computers all day, not moving much, what kind of conclusions would be drawn?
"We don't understand their language," he said, adding: "They're different, not better or worse."
Educating people to understand the lives of anacondas and their integral place in the llanos ecosystem is an important part of ensuring their survival, he says.
"Liking them is protecting them," says Rivas. "The more people know, the more they care, and the more they care, the more they conserve."
The anaconda's biggest enemy is man. "Wherever there are people, there are no anacondas," says Rivas.
Their habitat is shrinking and being degraded due to development. The llanos is being eyed by both the timber and oil industries. As more people move into the llanos, human-snake encounters increase, and the anacondas are often killed on sight because of their reputation as man-killers.
There are quotas under CITES (rhymes with nighties), an international treaty to protect endangered species of flora and fauna, that regulate the number of skins and live specimens that can be taken from the wild each year, but poaching is a problem.
Because of the anaconda's size and bad temper, says Rivas, it is relatively safe from the pet trade. But there is a market for their skins, and poachers favor the largest specimens, which are the females.
Rivas hopes that what he learns as he wades through the Venezuelan wetlands will contribute to the development of informed conservation guidelines to protect both the llanos and its creatures.
He hopes to eventually establish a preserve, a tourist lodge, and a market for ecotourism that will enhance the local economy, help educate people about the anaconda, and raise money for research.
"But without knowing what the anaconda eats, how it reproduces, how long it lives, where it lives, and its place in an ecosystem, the idea of protecting it or managing a population is impossible," says Rivas. And so he continues his pursuit of the green anaconda, walking in the shoes of the snake.
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