Reptiles
Anaconda
Eunectes · also called anacondas, water boa
An anaconda is a boa that took to the water and grew enormous. The green anaconda is the heaviest snake alive — a big female is as thick as a person’s thigh and can weigh more than 70 kg — and it hunts by lying almost submerged in a swamp, eyes and nostrils just above the surface, then seizing capybara, caiman, or deer, dragging them under, and squeezing.
Overview
Anacondas are the genus Eunectes, four species in the wetlands of tropical South America east of the Andes. The green anaconda of the Amazon and Orinoco is the giant; the yellow, dark-spotted, and Bolivian anacondas are all around 3 m. All are semi-aquatic constrictors with eyes and nostrils set high on the head for lying submerged, and all move far more easily in water than on land.
Heaviest, not longest
A big female green anaconda exceeds 5 m and 70–100 kg, by a wide margin the most massive living snake — but the reticulated python grows longer and more slender. Reliable anacondas top out near 6 m; the explorer stories of 10- and 30-metre snakes come from stretched skins, eye estimates, and fear, and a long-standing cash reward for a verified giant skin has never been claimed.
Breeding balls and giant females
Female green anacondas are several times the weight of males — one of the most extreme size gaps of any land vertebrate. In the breeding season, several males coil around one female in a slow breeding ball that can last weeks, after which she gives birth to 20–40 live young.
Status
All four species are Least Concern and stable, widespread across South America’s wetlands. The green anaconda is hunted for skins and killed out of fear near settlements; the yellow anaconda is harvested for skins in Argentina under a management programme. Verified fatal attacks on humans are essentially absent from the record.
Anaconda: common questions
What is the biggest snake in the world, the anaconda or the python?
It depends on whether you mean heaviest or longest. The green anaconda is the heaviest and bulkiest snake by a large margin, with big females weighing 70 to 100 kg or more and reaching around 5 to 6 metres, with a girth far greater than any other snake. The reticulated python of Southeast Asia is the longest, with well-documented individuals over 6 metres and a small number of reliable records approaching 7 metres, but it is a much more slender animal and a large one weighs perhaps half what a comparable anaconda does. So the anaconda wins on mass and the reticulated python wins on length.
How big do anacondas really get?
Much smaller than the legends claim. The green anaconda is the only species that reaches giant size, and carefully measured wild individuals rarely exceed 5 metres, with a few verified animals close to 6 metres and body masses around 70 to 100 kilograms in the largest females. Explorer accounts of anacondas of 12, 18, or even 30 metres go back centuries, and a reward offered by the Wildlife Conservation Society for a verified skin over about 9 metres has stood unclaimed for decades. The exaggerations come from the difficulty of measuring a thick, muscular, uncooperative snake, from skins that stretch by a third or more when removed, and from fear.
Do anacondas eat people?
Verified fatal attacks on humans by wild anacondas are essentially absent from the scientific record, despite the animal being large enough in principle to kill and swallow a person and despite people sharing its wetlands for thousands of years. Large anacondas can be dangerous if cornered, trodden on, or handled, and a serious bite followed by coils is a genuine risk to someone alone in the water, but the snake is not a habitual predator of people and generally retreats. The film image of anacondas hunting humans through the jungle has no basis in observed behaviour. Caimans and capybaras are the more typical large prey.
What is the difference between an anaconda and a boa constrictor?
They are both members of the boa family and both kill by constriction, but they differ in size, build, and lifestyle. The boa constrictor is a mostly terrestrial and semi-arboreal snake of forests and scrub across Central and South America, usually 2 to 3 metres long, relatively slender, and patterned with bold saddle markings, often kept as a pet. The anaconda is a genus of much heavier, water-bound snakes restricted to South American wetlands, with the green anaconda several times the mass of any boa constrictor. Put simply, a boa constrictor is a medium-sized snake that climbs, and an anaconda is a giant snake that swims.