Frequently Asked Questions
People interested in contributing with anaconda research and conservation can make a tax deductible donation via New Mexico Highlands University Foundation. Specify the Designation: "fund Dr. Rivas's Research. Molecular Ecology Lab". Make sure to drop me a note telling me about your contribution so I can make sure it gets to the right account. Some contributors to my research may be able to come with me to the field and participate in hands-on anaconda research with me and my team.
Anacondas occur only on the
tropical lowland of South America to the East of the
Most reptiles grow throughout their life but towards the later years growth tend to reduced remarkably. In anacondas very large anacondas that I caught at five meters (17 feet) did not grow an inch after I caught them in 5 years. As for what is the maximum size an anacondas can reach there has been a lot of controversy mostly for the "factor of fear". I am often quoted the size of a very large snake to be (your pick) 5, 7 10 or 20 meters in length. Most of the time the true size of the animals is a lot lower and everything has to do with "how afraid the person is" when he/she the anaconda. Another problem you may find is the fact that an anacondas with a recent meal will look substantially fatter than the would be otherwise. This can bias the appreciation of the observer that know what an anaconda, say, 4 meters long should look like. If s/he were to see an 4 meters long anaconda with a recent meal this person is likely to overestimate the size of the snake judging by its girth, as one seldom has the chance of seeing the whole animal stretched.
The truth is that to measure an anaconda is a difficult challenge. There are all sort of errors when you try to measure and animal that is stronger than you, wiggly, that do not stay straight and that is decidedly not cooperating. Here is a link to a more detailed description of the problems that you may have trying to measure a snake and what is the proper way to measure it (measuring). In the last 15 years I have measured more that 1000 wild caught anacondas and I believe that I have a good sample of what the size of anacondas really is. The largest anaconda that I measure was a little short of 5.5 meters (some 18 feet). I have good reasons to believe that they do not grow much bigger in the hyper-seasonal llanos but they may grow somewhat larger in the more flooded forest.
The largest snake in the world is with out a doubt he green anaconda. The reticulated python is a close contender as for it reporter length with reported compares very well, and some times favorably, with that of anacondas. However, we discussed here a couple feet difference of a snake at this size means very little mostly if they methods of measuring them are not very scientific. So for who is larger the question of length is not that important. If I were to ask what is the largest terrestrial mammal, somebody who knows his/her animals would answer without hesitation: the African Elephant. Nobody would start wondering and calculating how much taller giraffes are. Simple elephants are larger because weigh is a better indicator of size than length. In fact the view of thinking only of the length when we think of the size of a snake is an anthropomorphic position since snakes are rather long animals for our eyes.
Anacondas are a generalist predator and they eat pretty much anything they prey they can catch and subdue. Most of the diet of the smaller animals (young females and males) is composed of birds. There is an amazing array if wading birds and rich avifauna associated to the rivers and water bodies. Just about all of them are likely to be picked up by anacondas when they are not paying attention. After females reach certain size, their diet switches to larger, more energetic prey such as mammals and reptiles. In particular deer, capybara, turtles and caimans are a big part of their diet.
Surprisingly fishes are extremely rare on the diet of anacondas. Perhaps for the difficulty to catch a fish in the water by a large and sluggish snake or because they overlap little as the anacondas live mostly on stagnant water covered with vegetation which often means anoxic water where fishes are uncommon.
Anacondas, like most other snakes, are capable of eating prey that is formidable ticker than their own girth. This due to a combination of adaptations for just such a feat. Their skin and ligaments are formidably elastic to stretch as they swallow large prey. Not having an sternum their body can change shape when the swallow something very large. Perhaps the most amazing among the adaptations for large prey is the head of the snake. Head of the snake is better described as a high tech devise which purpose is to gulp large prey. The two sides of the mandible are join by an elastic ligament (not fused as in other vertebrates) both side of the maxilla re mobile too. The joins on the jaws (the hinge of the mandible so to speak) is a mobile join that allows it to move and stretch beyond what any other vertebrate could.
There is often the mistaken impression that the snakes "dislocates" the jaws or "unhinges" it to swallow large prey. Not of this is correct. A dislocation is when a join comes out of the place where it is supposed to be and often is associated with great pain, an injury. Unhinging a jaw is pretty much a dislocation and not what happens on the snake's jaws. If a person, or a vertebrate with a different head morphology were to open the mouth the way snakes do it would have to unhinge it and it would be an extremely painful (incapacitating) injury. However, this is a regular movement on the snake head. Such flexibility does not come without a price. Snakes had to give up the crushing power that most other vertebrates have on their jaws which renders them very vulnerable when they attack a prey.
This one of the questions that I am going after for longest. Since they are long lived vertebrates there is no way to know that unless we study them as long as they live. So far I have been studied them for 15 years and they live longer than that. I have caught animals that I marked 11 years ago, and they were adults when I caught them the first time. There is a record of an anaconda that lived in captivity for 28 years and was already an adult when she arrived there but this figure is not necessarily the same in the field as wild animals suffer, diseases, parasites and so on.
Part of my plan is to continue the study long enough to be able to answer this question in a scientific manner. This on itself is not an easy task as most funding institutions are glad to fund a project for a year or too but very few are interested in committing for a real long term study of the likes that is needed to answer this question. So far I have managed to sponsor the project with a combination of research funds, contribution from film makers as well as contribution from individuals that care about the animals and the research.
Anacondas are top predators that often prey on animals stronger and tougher than humans. A medium size anaconda, say 13 feet long, can easily kill an adult person. Some people believe that anacondas would not be able to pass the shoulders of a person. This is untrue. Anacondas can swallow prey thicker than a person plus the shoulder of a human a not a very mobile joins and the snake can easily disarticulate the joins of the rotator cuff making it less bulky. The reason that there are not many records of anacondas preying on people is because anacondas live in the swamp where people do not go very often. In fact, the two records of anacondas attacking humans have been on people that were helping in my research. When we go to the field we spend inordinate amounts of time on the habitat of the anacondas and increase tremendously the chances of an encounter. The bad news is as human encroach on anacondas habitats as a result of the so called development that every time leads people's frontiers more and more into habitats of the wildlife.