Green anaconda

Identification

The green anaconda is a very thick, heavy snake, and it is considered the heaviest snake species in the world². It is dark olive with large black spots; the spots on the sides have paler centres, a pattern that blends in with water plants². Its eyes and nostrils sit on top of the head, and males have longer spurs beside the vent than females².

Females grow much larger than males: across 780 wild anacondas caught over seven years in the Venezuelan llanos, females averaged 3.1 m and 20 kg, and no male was longer than 3.39 m². The largest was a female of 5.21 m and 97.5 kg². Reports of anacondas 9–11 m long have long been debated, and none near that size was found².

Distribution

The Reptile Database lists the green anaconda from Venezuela, Colombia, Ecuador, north-eastern Peru, northern Bolivia, eastern Paraguay, Brazil, Guyana, French Guiana and Trinidad, and a 2024 study also includes Suriname^1,3. It lives in the lowlands of tropical South America east of the Andes².

In 2024, researchers proposed that anacondas of the Orinoco basin, the Guianas, Trinidad and Amazonian Ecuador form a separate species, the northern green anaconda (Eunectes akayima), based mainly on genetic differences³. The Reptile Database does not yet accept this split: it treats E. akayima as a synonym of E. murinus, because the two cannot be told apart by their appearance¹.

Habitat

The green anaconda is semi-aquatic, and much of its body shape is adapted to life in water². In the Venezuelan llanos it lives in seasonally flooded savanna, marshes and rivers². As the savanna dries out, anacondas shelter in drying mud, in caves in river banks, in cracks in the dry ground and under bushes beside the remaining water².

Behaviour

Anacondas are sometimes called nocturnal, but in the llanos they were seen moving, hunting and mating at all hours, with the most activity late in the day and early in the evening². They use quite small home ranges in each season, but make long moves between their wet-season and dry-season areas². Pregnant females spend much of their time basking on banks, floating plants or termite mounds².

Many young anacondas die in their first years, and adult males face a high risk of being killed by caimans².

Diet

The green anaconda is an ambush hunter that kills its prey by constriction². Young snakes eat mostly wading birds, then switch to larger prey as they grow². In the Venezuelan study, about half of the prey were birds such as jacanas, ibises and whistling ducks, and the rest were large mammals and reptiles, including capybaras, white-tailed deer, spectacled caimans, river turtles and other anacondas².

A review of published records found that birds are the prey taken most often, followed by mammals, and anacondas sometimes eat other anacondas^2,4. The review found no record of an anaconda eating a human in the scientific literature⁴.

Reproduction

The green anaconda gives birth to live young². In the breeding season, one female may be courted by 1 to 13 males at once, forming a “breeding ball” that can last up to four weeks². Pregnancy lasts about 200 days, and pregnant females do not feed².

In the Venezuelan study, litters had 5 to 74 young, with an average of about 29². Newborns were about 79 cm long and weighed about 220 g². There is also evidence that females can occasionally produce young without mating (facultative parthenogenesis)¹.

Venom and medical significance

The green anaconda has no venom; like other boas, it has no venom glands or venom-injecting fangs⁵. It kills its prey by constriction². Large anacondas are very strong, and even researchers had to develop special methods to restrain and measure them². Despite its reputation, a review of the scientific literature found no recorded case of an anaconda eating a person⁴. Anyone bitten should get the wound checked by a doctor.

Conservation

The green anaconda is listed as Least Concern on the IUCN Red List (published 2021)⁶. That assessment was made before the 2024 proposal to split the species^3,6. International trade is controlled under Appendix II of CITES⁷.

Large females are especially important to populations: in the llanos, females over 3.4 m produced about 60% of the young born each year, so hunting the biggest snakes could cause sharp declines².

Similar species

The boa constrictor (Boa constrictor) is the other large constrictor of tropical South America that people may mistake for an anaconda; both are harmless to people who leave them alone^5,9. The boa is cream or brown with dark saddle-shaped bands that turn reddish towards the tail, and has three dark stripes on the head⁹. The anaconda is dark olive with round black spots, and its eyes and nostrils sit on top of the head². These differences are not a safe basis for handling any snake. Keep your distance from every snake you cannot identify.

In captivity

The green anaconda is not a suitable pet: it grows very large and is so strong that even researchers needed special methods to handle it². In captivity, anacondas have been reported to live more than 20 years². In the United States it has been listed as injurious wildlife since 2015, so live animals cannot be imported without a special permit⁸. International trade needs CITES permits⁷.