Despite its fame and horror film notoriety, very little is known about the anaconda. One man who has got to grips – quite literally – with this giant serpent is Jésus A Rivas… Here he explains what you need to know about this fearsome predator
One of the most feared snakes on the planet the green anaconda is the second longest snake in the world, and the heaviest.
How big is the green anaconda?
The green anaconda is the heaviest snake in the world, with females known to exceed 100kg in weight and reaching 7-8m long. Males are smaller – in fact they are approximately half the size in length.
Where does the anaconda live?
The green anaconda lives in sultry South American ( Venezuela, Brazil, Colombia, Ecuador and northern Peru) swamps where temperatures tend to exceed 30°C year-round. Submerged underwater, it is impervious to leeches, bugs and all the other tropical invertebrates that would drive a human out of his or her mind.
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What do green anacondas look like?
Green anacondas are olive-green in colour, with dark oval spots along their spines anacondas are designed to perfectly blend into their swamp habitat. They have yellow and black scales on their belly, while there are two dark stripes from their eyes to their jaws.
Their nose and eyes are located on the top of their heads to help aid them see and breathe when swimming in the water.
Are green anacondas good swimmers?
Green anacondas are excellent swimmers, able to stay under water for 10 minutes and able to reach speeds of 16 km/h
What do anacondas eat?
Green anacondas eat mammals including wild pigs, deer and capybaras; reptiles including turtles and caimans; waterbirds.
When it comes to eating, the anaconda is capable of swallowing prey nearly as large as itself. Can we even conceive of gulping down 60kg of meat in one sitting, taking eight hours to swallow it?
Are green anacondas cannibalistic?
Green anacondas sometimes indulge in cannibalism – usually involving the larger female devouring the smaller male.
How do anaconda find their prey?
Let’s begin by considering the simple act of finding a meal. For humans, this is usually hazard-free. But not for the anaconda, particularly the larger female that hunts the biggest prey. She usually lurks in a swamp close to the shore where big mammals such as white-tailed deer come to drink.
At other times, she may lie in wait in the water beside a path through a wetland that is regularly used by animals such as caimans or capybaras to move from one area of water to another.
How do they catch their prey?
The anaconda blends in with the submerged vegetation, only her eyes and nostrils breaking the surface of the murky water. When prey comes within range, she tenses her muscles and springs, seizing it in her jaws anywhere she can get a good grip with her fangs. This is not the killer blow, however – it merely provides an anchor for her coils, which come flying out of the water and wrap around her victim at lightning speed.
The snake may have barely moved for months. Such immobility would atrophy a human’s muscles and incapacitate them. However, an anaconda has the latent strength to subdue a 3m-long crocodile after months of waiting, and squeeze it so tight that its heart can no longer fill up with blood and the victim expires.
And this is not the only challenge that arises from attacking large prey. Every time a female anaconda ambushes a caiman, she risks serious injury, as the crocodile’s jaws are far more powerful than her own. The anaconda’s jaws are best viewed as a high-tech device that is perfect for specific functions.
While a typical lizard’s head contains a system of hinges and levers that enable it to deliver a powerful bite, an anaconda has lightweight, movable joints. The level of jaw mobility that allows this snake to swallow very large prey comes with a price tag: a lack of crushing power and a vulnerable skull that offers little protection to its brain.
This lack of weaponry is also exposed when an anaconda tackles prey such as capybara. Imagine a rat the size of a Rottweiler and you have a capybara: all teeth and attitude. In the struggle for survival, these feisty rodents often inflict severe wounds on attacking anacondas, and sometimes these injuries prove fatal. Therefore, it is imperative that the snake uses all of its skills and strength to subdue its prey swiftly.
How often do anacondas eat?
When you realise that catching a meal can be very dangerous, it’s no longer surprising that anacondas don’t do it very often. Putting ourselves in their shoes helps us to understand why these reptiles wait so long between meals. My data suggests that a large female may feed as little as once a year, though three meals is more usual. She spends most of her time resting and waiting, using up as little energy as possible for movement.
Do anacondas attack and eat humans?
Are humans on an anaconda’s menu? It may surprise you to learn that there are no documented records of this snake eating a human. This doesn’t mean that it has never happened. Indeed, two of my research assistants have been attacked in the field. On the first occasion, the anaconda only failed to drag the female researcher into the water because her trousers tore at the knee, preventing it from getting a good grip. The second time, I managed to deflect the snake’s strike before any real damage was done.
Though anacondas are not man-eaters by nature, they will take any prey they can subdue and swallow. And they can certainly extend their jaws wide enough to get around an adult human’s shoulders (our widest point), so the potential exists for them to prey on people. The main reason why they don’t is because we avoid the places where they thrive. But as we encroach into their habitats, we should expect greater conflict with these snakes.
How do anacondas mate?
Looking at things from an anaconda’s point of view has helped me to unravel other mysteries surrounding the species, namely its mating behaviour. These snakes gather in breeding aggregations of one female and up to 13 males.
The resultant mating ball looks like a gigantic bowl of spaghetti, with all the males coiling around the female, trying to push each other out of the way as they compete to couple their tails with hers. Typically, the larger males use their greater strength to displace the smaller ones from pole position, and tend to be the only ones that have a realistic shot at breeding.
So, you might assume that male anacondas would grow as large as possible so they can gain the greatest advantage. But, in fact, they’re not very large at all. At 6.5kg, they weigh only a fraction of the female. So why are males this small if sexual selection favours a larger size?
During my research, I realised that it was possible reliably to identify the sex of an adult anaconda at a glance: males rarely grow heavier than 10kg and all other snakes above this weight are female. If I could use size to determine gender, could anacondas also use it to recognise the opposite sex?
These snakes have a superb sense of smell that would certainly help them to distinguish male from female. But when I imagined myself as a male anaconda in a mating ball, I realised that my head (including my chemosensory and visual organs) would probably be somewhere under the muddy water, while my tail was wrestling with the others to get hold of the female. In this scenario, I would have to rely on tactile cues to figure out who was who.
And it’s not a perfect strategy by any means. By watching breeding aggregations containing relatively big males, I discovered that some individuals mistook one of the larger males for the female and tried to mate with him. Clearly, males that choose the wrong target – and their unfortunate victim – lose precious time and waste their reproductive effort. It would appear that being big can be a problem sometimes – only males that are large and strong enough to displace rivals, but small enough not to be confused with a female can mate successfully. This explains why most males are 6–8kg, while females are much more varied in weight.
How long is the gestation period?
Eggs are incubated and hatch within the female’s body over a seven-month period. She gives birth to 20–30 live young, which are up to 90cm long at birth.
How long do anacondas live?
The lifespan of an anaconda in the wild is about 10 years
Why we should love the green anaconda
Anacondas live in a very different world to us – not only physically, but also cognitively. They inhabit stagnant water in swamps covered by aquatic vegetation: the last places on Earth we would choose to live. And their thought processes are even more difficult for us to comprehend. These differences hinder our ability to understand this snake’s life and ecology, and ultimately our capacity to protect the species. Only by doing our best to understand the anaconda on its own terms can we learn enough to live in harmony with this wonderful reptile.
Anaconda myths and legends
Large, predatory animals seem to attract tall stories. In the 18th and 19th centuries, European explorers of Amazonia often returned with tales of 30m-long man-eating anacondas. These have never been verified, but have spawned horror movies such as Anaconda, blackening the snake’s reputation.
Local folklore is kinder to these snakes, depicting them as guardians of rivers and forests. At the annual Parintins Festival in Brazil, there is a dance that tells the story of a young man who grows up to become a giant anaconda, only reverting to human form at night. His many friends try everything to break the spell, but to no avail. This poor man-snake is said to roam the rivers to this day.
Who is Jésus A Rivas?
Dr Jésus A Rivas is biologist, graduated from the Universidad Central de Venezuela, famous for his research into the green anacondas and author of the book Anaconda: The Secret Life of the World’s Largest Snake. His research interests also include natural history, tropical ecology, invasion ecology, ethology, and conservation.