Green Anaconda (Eunectes murinus): Facts, Size and Habitat

What does a green anaconda look like?

The green anaconda is a thick, heavy-bodied snake with an olive-green to dull greenish-brown back covered in large, round black blotches. Along the sides runs a row of smaller black spots with yellowish centers, and the belly is pale yellow or cream with dark markings. This pattern blends well with murky water, mud and floating plants.

The head is relatively narrow for such a massive body. A black stripe runs back from each eye toward the jaw, usually edged with orange or yellow. The eyes and the nostrils sit on top of the head, so the snake can breathe and watch the surface while almost its whole body stays hidden underwater. Like all boas, it has two small claw-like spurs beside the vent, the last traces of hind legs. Males have larger spurs than females.

The skin is soft and loose, and the scales are small and smooth. Young anacondas look like small copies of the adults, with brighter colors that darken with age.

How big is the green anaconda?

The green anaconda shows one of the largest size differences between the sexes of any land vertebrate. Adult females usually measure 3.5 to 5 m (11 to 16 ft) and weigh about 30 to 80 kg (66 to 176 lb). Males average around 3 m (10 ft) and weigh only a fraction as much. Field studies in Venezuela have found females to be several times heavier than males of the same population.

The largest wild anaconda measured by researcher Jesús Rivas, who examined hundreds of anacondas in the Venezuelan llanos, was a female 5.21 m (17 ft) long weighing 97.5 kg (215 lb). The longest verified captive specimen, a female at the Pittsburgh Zoo, reached about 6.27 m (20 ft 7 in) before she died in 1960. Reports of anacondas 9 to 12 m (30 to 40 ft) long have never been backed by a preserved specimen, a skin that was not stretched, or a scientific measurement.

For the full story of record claims, measuring problems and the famous unclaimed reward for a 30-foot snake, see how big is a green anaconda?.

Where do green anacondas live?

Green anacondas live in tropical South America east of the Andes. Their range covers the Amazon and Orinoco river basins and the Guiana Shield, including Colombia, Venezuela, Trinidad, Guyana, Suriname, French Guiana, Brazil, Ecuador, Peru, Bolivia and northern Paraguay.

They are tied to slow or still fresh water: swamps, marshes, oxbow lakes, flooded forest, slow streams and the seasonally flooded grasslands of the Venezuelan and Colombian llanos. They are clumsy on land but move smoothly and quickly in water. When pools shrink in the dry season, anacondas crowd into the remaining water, and some bury themselves in mud and stay inactive until the rains return. More detail on the range and habitats is in where do anacondas live?.

What do green anacondas eat?

The green anaconda is an apex predator that eats almost any animal it can overpower. Young snakes take fish, frogs, small birds and baby caimans. Adults catch wading birds, turtles, caimans, iguanas, agoutis, pacas, peccaries, deer and especially capybaras, the world’s largest rodent. Very large females occasionally take prey as big as a tapir.

An anaconda is an ambush hunter. It waits in shallow water, often with only its eyes and nostrils showing, and strikes when an animal comes to drink or wade. It grips with its teeth, throws coils around the prey and squeezes, which cuts off blood flow and quickly kills it. Prey caught in water may also drown. The snake then swallows its meal whole, head first.

Meals are often large, frequently 14 to 50 percent of the snake’s own weight. Because its metabolism is slow, a big anaconda can go weeks or months without eating after a large meal. Females sometimes eat males after mating. The full menu is covered in what do anacondas eat?.

Behavior

Green anacondas are solitary for most of the year and mostly active at night and around dusk. They spend much of the day resting in shallow water, under floating plants or basking on banks. They are strong swimmers and can stay submerged for long periods.

Like other snakes, anacondas find their way mainly by smell, flicking their forked tongues to pick up scent particles. They also sense vibrations through the water and ground. Adults are not great travelers on land and tend to stay in the same marsh, lagoon or stretch of river for long periods, moving mainly when water levels rise or fall with the seasons.

When threatened, an anaconda usually tries to slip away into the water. If cornered or handled, it may hiss, bite, or smear a foul-smelling musk from its vent. It is not aggressive toward people, but a large one is strong enough to cause serious injury, so wild anacondas should only be watched from a safe distance.

Breeding balls and live birth

Anacondas mate in or near water, mostly during the dry season, which in the Venezuelan llanos runs roughly from March to May. A female leaves scent trails that males follow. Often several males find the same female and wrap around her at once, forming a “breeding ball” of up to about 12 males. The ball can stay together for two to four weeks as the males push and jostle slowly for position. The female is far bigger than her suitors and has a say in which males mate with her.

The green anaconda is ovoviviparous: the eggs develop and hatch inside the mother’s body, and she gives birth to live young after six to seven months. A litter usually holds 20 to 40 babies, and large females occasionally produce more than 80. Births happen in shallow water. Newborns are about 70 to 80 cm (28 to 31 in) long and around 200 g (7 oz), and they get no parental care.

A female may lose up to half her body weight during pregnancy and birth, and she eats little or nothing while pregnant. Because of this cost, females probably do not breed every year. In 2014 a captive female in England produced young without a male, an example of parthenogenesis, or “virgin birth,” which is known in several boas and pythons.

Lifespan

In the wild, green anacondas are thought to live about 10 years on average, although exact wild lifespans are poorly known. In zoos they often live for more than 20 years and can exceed 30 years. They keep growing throughout life, quickly at first and more slowly after reaching maturity at about three to four years old.

Predators and threats

Baby anacondas have many enemies, including caimans, large wading birds, big fish, otters and other snakes, and many do not survive their first year. Adults have few natural predators. Jaguars, black caimans and Orinoco crocodiles are known to kill even large anacondas on occasion. Read more about one of those predators in our jaguar profile.

The main threats from people are habitat loss as wetlands are drained or converted to farmland, killing out of fear or to protect livestock, and collection for skins and the live animal trade.

Conservation status

The IUCN Red List classes the green anaconda as Least Concern, in an assessment published in 2021. The species has a very large range, much of it remote, and it remains common in many protected wetlands. International trade is regulated under Appendix II of CITES, which requires permits to show that exports do not harm wild populations.

Outside South America, the species is a concern as a possible invader. Florida added green anacondas to its prohibited species list in 2021 after a handful were found in the wild, although no breeding population has been confirmed.

Myths and facts

Myth: Anacondas grow to 12 m (40 ft) or more. Explorers’ tales and films describe giants of 12 m (40 ft) or more, but no such snake has ever been measured by scientists. In 1937, members of an expedition in Guyana guessed the length of a coiled anaconda at between 6 and 18 m (20 and 60 ft); when measured, it was 5.9 m (19 ft 4 in). Overestimates are the rule, not the exception.

Myth: The name “murinus” means mouse-colored. The Latin word can mean “of mice.” In the original 18th-century descriptions, it referred to a snake that lies in wait for mice and rats, not to gray coloring.

Myth: Anacondas regularly eat people. There is no verified case of a green anaconda eating a human. Large reticulated pythons in Asia have killed and swallowed people, but anacondas live mostly in remote wetlands. For a side-by-side look at the two giants, see anaconda vs python.

Is there a second green anaconda species?

In 2024, a team led by Jesús Rivas published a study proposing that northern populations, from Venezuela, Trinidad and the Guianas, belong to a separate species, the northern green anaconda (Eunectes akayima). The name comes from a Carib word meaning “the great snake.” The proposal was based mainly on genetic differences, as the two forms look almost identical.

Other herpetologists questioned the split, arguing that the genetic and physical evidence was not strong enough, and many authorities continue to treat all green anacondas as one species, Eunectes murinus. This article follows that traditional view. The genus also includes smaller relatives: the yellow anaconda (E. notaeus) of the Paraguay River basin, from the Pantanal south to northern Argentina and Uruguay, the dark-spotted anaconda (E. deschauenseei) of northern Brazil and French Guiana, and the Beni anaconda (E. beniensis) of northern Bolivia. The last two are sometimes merged with the yellow anaconda.