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Home > Resources > Extreme Scientists > Herpetologist

Herpetologist: Jesus Rivas

Hardworking Herpetologist

Dr. Rivas carrying a female anaconda he captured for studying in the field. All of the snakes captured and measured were later released back into the wild.

Dr. Jesus Rivas makes a living wrestling some of the biggest snakes in the world in the llanos of Venezuela, where some of these huge snakes live. The work involves long hours enduring the heat of the tropics slogging through the marsh weeds (riddled with leeches) in bare feet "feeling" for the unmistakable shape and texture of an anaconda with the sensitive skin of his feet and toes. Using primitive, but effective tools like cotton socks and plastic electricians' tape, he captures and restrains them to gather blood and tissue samples so we can all understand more about them.

Dr. Rivas has always been fascinated by snakes and other wildlife, ever since he was a boy growing up in Venezuela. While other boys were playing superhero he was captivated by the beautiful and exotic creatures that lived in the wild near his childhood home, even keeping a 'nature diary' with drawings of the creatures he admired. As a youngster he had been repeatedly warned by his parents not to touch snakes and other wild creatures because many of them in that part of the world are dangerous, even poisonous. He didn't really get an opportunity to get up close and personal with snakes until he was a teenager and eagerly volunteered his time at a local zoo.

Part of his responsibilities at the zoo were to clean the animals' pens and cages as well as feed them, which is where he got his first opportunity to observe large anacondas killing and devouring their prey. This early exposure to the captive reptiles inspired him to want to learn more about the way these creatures lived in the wild. When he later entered college at the Universidad Central de Venezuela he chose to study biology.

Dr. Rivas got his first real opportunity to do field research on the giant green anaconda when a project 'fell into his lap'. Because of the creative and pioneering work that he had done studying green iguanas in the field he was the first person to come to mind when the Wildlife Conservation Society began to round up some people to conduct a field study of anacondas.

Jesus Rivas holding an anacondaHis research would be the first of its kind ever performed on the green anaconda, as no one had carried out any field studies of this species before. Very little was known about the elusive green anaconda and the Wildlife Conservation Society, together with the Convention for the International Trade of endangered Species (CITES), and Profauna (the Venezuelan Fish and Wildlife Service), funded a project to study this species to understand more about it and try to develop a management plan.

During his years of field research on the anaconda, Dr. Rivas and his research team developed practical and pioneering ways to capture, subdue and measure some of the biggest snakes in the world without endangering themselves or harming the snakes.

Dr. Rivas has since spent 11 years on the llanos capturing and studying anacondas in the wild to understand more about them. Here some of the cool things he did learn from his research so far:

1) anacondas have the largest sexual size dimorphism (difference in size between the males and the females) of any vertebrate species (males are 1/5th the size of females!)

2) when anacondas mate a large number of much smaller males will wrap themselves around one large female, forming a "breeding ball", where the males compete in very close quarters for the opportunity to mate

3) anacondas also present a surprising ontogenetic change in biomass from birth to adulthood, with a 500-fold increase it is much higher than the increase found in any other species of snake

4) In his years of field research on the green anaconda, Dr. Rivas has captured and 'processed' over 900 anacondas!

Dr. Rivas and his wife and research partner Renee carrying a tired snake in to collect data.

What's it Like to Handle a Huge Green Anaconda?

According to Dr. Rivas, "It takes an average of about 15-20 minutes of fighting with a snake before it tires to the point of exhaustion. Then it becomes easier to handle and more compliant." Because of the large difference in size between males and females, all of the really large snakes he has captured are females (the "big girls" he calls them). Many of the large snakes he has captured weigh between 80 and 100 lbs. (36-45kgs). Can you imagine trying to wrestle with 100lbs/45kgs of writhing snake? And then multiply that over 900 times!

There's still a lot that is not known about them that can only be learned from long-term studies conducted by continually tracking and observing them in their native habitat. Dr. Rivas is currently looking to fund continuing research of these fascinating and enigmatic creatures by offering eco-tours of Venezuela and an "Adopt-a-snake" program. You can read about his research, see lots of great photos of anacondas, and support his research by visiting his website at: anacondas.org. Check it out!!

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