Field Herp Diaries: Anaconda Expedition

Anaconda. Photo credit: Fernando Flores
Anaconda. Photo credit: Fernando Flores

By J.P Dunbar, HSI Science Officer.

Ever since I was a teenager I was fascinated by giant constrictors, and in particular, the green anaconda of South America. Of all the giant snakes, the anaconda is arguably the most mysterious, perhaps due to the fact that its aquatic lifestyle in the vast flooded savannahs keeps it far from the reach of most human settlements.

Seeing a green anaconda in its natural habitat was something I have always wanted to do. In March 2007 I had the chance to do just that, when my wife Teresa and I jumped at the opportunity to join Dr Jesus Rivas and his wife Dr Sarah Corey Rivas on a research expedition to the Llanos region of Venezuela… to catch green anacondas!

As we left Caracas and drove on a straight road for several hours into the wilderness, I was struck by how quickly the landscape shifted from an urban setting, to farmland and finally to vast swamplands teeming with spectacled caiman. After several hours we reached Hato El Cedral, a cattle ranch of approximately 54,000 ha. This habitat was remote and very wild, with caimans roaming right up onto the road. The excitement was overwhelming! We arrived at the ranch just in time for dinner with the team of scientists, and we planned our anaconda hunting adventure for the days ahead.

Some of the many caiman we encountered on our trip.
Some of the many caiman we encountered on our trip.

Finally, the sun rose and the alarm calls from the local howler monkeys heralded the morning we long anticipated. Time to finally go anaconda hunting! On our first hunt, we trekked through the swamps for quite a distance without seeing a single snake. We were about to turn back for lunch when I saw, with the corner of my eye, a little black-spotted green snake on the surface of the swamp. It was very well camouflaged among the hyacinth but there could be no mistake, it was an anaconda! To my surprise it was constricting a duck! It seemed a very large prey item for

My first little anaconda!
My first little anaconda!

such a small snake. I suddenly realised, this was my first wild snake!

Occasionally we would come across capybaras, the size of sheep, partially submerged in the swamp to escape the suns’ rays. They are capable of giving a serious bite, or knocking you off your feet if you startle them. I did accidently step on one or two, but luckily they charged off in the opposite direction.

Mid-day is too hot to go searching, so we used this time to process the snakes we’d found the previous night and that morning. We recorded anatomical variables and signs of previous conflicts (we got one with a perfect circular bite mark from a Red Belly Piranha). As Dr Rivas’ research involved a mark and recapture program, we also checked each snake for identity markings to determine if they are recaptures. If it was not a recapture we then got to name it, and I am proud to say there is a green anaconda somewhere in the South American swamps named after me! (Hopefully he is still thriving and hasn’t become a meal for some other animal). Some of the larger females appeared emaciated, as they had given birth the previous season and needed a few years to regain weight. However, some large females had already recovered from previous breeding seasons and were so vigorous and feisty, they needed to be restrained.

Dr. Rivas with an emaciated animal
Dr. Rivas with the female that had been recaptured after 13 years.

This was achieved using a technique Dr Rivas described, which involves putting a sock over the anaconda’s head and then taping the sock behind the head so it doesn’t slip off. Then the jaws are taped shut between the eyes and the nostrils, firmly, but not too tight. This will help calm the snake and also prevent it from biting. It is important that the animal hasn’t had a recent meal that it might regurgitate. You must not hold the jaws closed too tightly (as you would with crocodilians) because the teeth on the upper jaw may penetrate the tissue on the lower jaw and vice versa, causing bleeding. Finally, the head and sock must not get wet, as this could cause the tape to come loose, potentially obstructing the nostrils, which could cause suffocation. Once we had finished recording data, we released the anacondas unharmed. Releasing a bag of anacondas is a very rewarding experience!

Releasing an anaconda after data collection
Releasing an anaconda after data collection

The Llanos is home to a diverse array of wildlife. We encountered many species of frogs, lizards and turtles, and birds dotted the landscape for miles. On one morning trek we found a Llanos sideneck turtle on its back. It was approaching mid-day and if it did not right itself, it risked perishing in the tropical heat. We decided to jump down and help the turtle. The bank was covered with large basking turtles and caiman, soaking up the sun’s rays and when they saw us approach, they quickly made a dash for the security of the water.

This little guy was in a spot of trouble before we found him.
This little guy was in a spot of trouble before we found him.

One morning, after a couple of hours’ searching, one of the team members, Tom Hogan, returned to the group with a large female anaconda. It was difficult to appreciate her size as she was long but emaciated. Dr Rivas surmised she had given birth the previous season and had yet to acquire a substantial enough meal to recover. Some of her wounds suggested she had tried and failed to capture prey. During data collection we realised we had recaptured an individual that had first been collected 13 years prior, offering interesting insight into this species’ longevity in the wild. Despite this female’s sorry state, Dr Rivas had observed animals in a similar condition returning to good health shortly after acquiring one or two large meals, and he was quite confident that this individual would also recover.

I was very eager to get some hands on experience with wild caiman. My first encounter came one evening when we came across a nursery of a few hundred baby caiman. The female guarding the nursery was not seen. We ventured into the muddy pond, hearts pounding with excitement as baby caiman dashed everywhere, around us! I put my two hands down and gently picked up a handful of babies. These were my first wild crocs! More encounters were to come and they only got bigger!

Who said crocodiles couldn't be cute?
Who said crocodiles couldn’t be cute?

Although I had been involved with reptiles for over a decade, I had not yet held a large crocodilian, with the exception of a large, captive, American alligator that had already been restrained. I wanted the experience of catching and securing a wild crocodilian. The opportunity came one evening when we came across a dry muddy patch with no deep water for caiman to escape to. They were bogged down in the mud. My first encounter with a large caiman came as I accidentally stood on one that was concealed beneath the mud. It was quite surreal to feel the bony scales of its back, on my bare foot. In my surprise, and excitement, I did everything I shouldn’t have. The caiman had not moved (It may have been playing dead, or was estivating) so I decided that if I could locate the tail, I could pull it from the mud. I reached down, put both hands on the caiman’s back, but I misjudged the base of its tail. As I moved my hands down the ‘tail base’ I could feel the caiman’s teeth running past both of my hands! When I realised my mistake I quickly withdrew my hands, and jumped a step back. My eagerness nearly got me into trouble. I decided next time I would not try it alone, but would wait for the supervision of Dr Rivas. Due to the location being dried up, quite a few caiman in this area were isolated from the deeper swamp and it wasn’t long before we encountered another big caiman. This time, I was following Dr. Rivas’ advice on how to approach the situation, but I rushed in too fast and grabbed the caiman by the neck, before using the weight of my body to hold it down. The caiman swung around like crazy, breaking free from my grip as I fell flat on my back. It ran off through the mud and we all had a good laugh at how terrible I was at catching crocs! However, I am quick to learn from my mistakes and that was all about to change. Later that evening we came across yet another large caiman, and this time I knew what to do. I positioned myself on its back while simultaneously holding the neck, this time I knew I had a strong hold and that my body weight would keep the caiman secured. I had done it. I’d caught my first wild adult caiman! She was a nicely sized caiman and in great shape. I let her go and she ran off into the muddy swamp. I felt very lucky to learn so much about croc handling without harming the animals, or myself. I reflected on my early mistakes and have been acutely aware of them every time I’ve had to catch one since.

JP With Caiman

One afternoon we decided to take a boat trip up the Apure River, it was a nice opportunity to relax and enjoy the habitat and the wildlife around us. We got to see amazing birds high up in the trees, some of which were quite large, and looked out of place sitting so high up on the branches. During the dry season, life is very different for the reptiles of the deep river compared to their counterparts residing in the dried up swamp. We couldn’t resist the opportunity to do a bit of piranha fishing. When we returned the fish to the water, the hungry raptors seized the opportunity of a free lunch, swooping down to grab them before the caiman got to them. We decided that this experience would be enhanced if we went at night, to observe nocturnal behaviour and so we returned a day or two later. It was quite spectacular; fish were erupting from the river, literally landing in the boat and even hitting us in the face as we cruised up the river. We never stopped to do a spot of fishing, but we still managed to return to camp with a big

Caiman are capable of explosive bursts of energy. Seeing this guy breach so dramatically was pretty special.
Caiman are capable of explosive bursts of energy. Seeing this guy breach so dramatically was pretty special.

bucket of fish! Using high powered lamps, we observed the caimans fishing!  This was an incredible sight to behold. They are very skilled; using their long bodies and tails, they trap fish in the shallow water just inches away from the river bank, and then quickly snatch any that approached their jaws.

We hit the road one evening for some nocturnal Jaguar-spotting. We got to observe some amazing nocturnal behaviour from Giant anteaters, foxes, deer and other grazing animals. We didn’t see any Jaguars but we did find fresh tracks from earlier that day, so we got close! Prior to arriving in South America, I had only ever worked with captive snakes. While some were quite large, and often temperamental, I had no idea how they would compare to wild green anacondas. I knew to expect them to be snappy, after all, they would be afraid of me so why wouldn’t they defend themselves? After a few captures I realised that my experience handling large captive snakes was a great asset, as I could anticipate their behaviour. There really wasn’t much to it, put simply: if you’re not quick enough, they will bite.

There was one particular innate behavior we could always anticipate: the infamous ‘evil loop’. This was a term coined by Dr Rivas, describing the defensive manner in which wild anacondas quickly pull their heads into their coils when grabbed. We needed to keep this in mind every time we secured one behind the head. Almost every time we did, this classic behaviour kicked in to play. The problem is, if the coil pushes your hand off you could quickly find your hands wrapped up in the snakes coils, while its head is free to bite! That being said, once you are aware of this behaviour it is not difficult to avoid losing your grip.

Collecting data from a specimen.
Collecting data from a specimen.

On our last evening, one task had yet to be achieved: Teresa had yet to catch her first anaconda! We set out on the evening’s hunt. Until now, I had spotted my anacondas ahead of me, while other team members found them by stepping on them in their bare feet (the most commonly used search technique), but Teresa showed me up and proved she was the true anaconda-hunter among us! Teresa had spotted tracks in the mud and followed them to a protrusion of mud that resembled a snake. These casts were the result of mud drying around a submerged snake, and were frequently empty when we encountered them, but occasionally they did yield a snake. This time we got lucky. We knew this was a fresh cast because we spotted two nostrils protruding above the muddy surface. Following instructions from Dr Rivas, Teresa went for the grab, securing the snake behind the head as she pulled it up from the mud. Teresa and I, both thought that maybe the mud and debris covering the snake’s eyes were calming her, but even as Teresa cleaned her off, she remained calm and pleasant. Our adventure couldn’t have ended better. This individual had not been previously captured, therefore Teresa named her ‘Medusa’ after the Greek Goddess. This was a great moment for us and was celebrated with many cheers (and later with some Venezuelan rum)! The following morning, after we collected our data, she was released back into the swamp in the same location.

Medussa up close!
Teresa getting up close and personal with Medusa!

Throughout the expedition, we captured 36 anacondas in total. The majority were moderately sized individuals 1-3 metres in length, but we also captured some juveniles and several large females in excess of 3.5 metres. I had previously seen wild lizards and turtles in Southern Europe and the Caribbean, but this was my first opportunity to see, and catch, wild snakes and crocs in their natural habitat. I was expecting this trip to be an adventure, an experience that would surpass any packaged holiday, but it became much more than that to me. It really was a life changing experience. On the plane journey home I decided I would quit my job, study biology and work with reptiles.

If you would like to learn about green anacondas, visit

If you are interested in visiting the Llanos or donating to anaconda research contact Dr Rivas at

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JPAbout the author: John is an Irish herpetologist working at the Herpetarium in the Alistair Reid Venom Research Unit, at the Liverpool School of Tropical Medicine. He is also a Science officer with the Herpetological Society of Ireland.

Photo credits:

Featured image by Fernando Flores. Used under license. View Fernando Flores’ Flickr.

All other photos supplied by JP and Teresa Dunbar.