Heaviest species of snake
Southern green anaconda, Eunectes murinus, Northern green anaconda, Eunectes akayima
300+ kilogram(s)
Not Applicable ()

The heaviest species of snake is the green anaconda, native to wetlands and slow-moving rainforest rivers of tropical South America and Trinidad. In February 2024, the long-recognized single species of this large constrictor was split into two based on genetic and geographic differences: the southern green anaconda (Eunectes murinus) and the northern green anaconda (Eunectes akayima). Fully grown, females of both species obtain a typical weight of between 30 and 70 kg (65–155 lb), measuring 3–5 m (9 ft 10 in–16 ft 4 in) from head to tail. Occasionally much larger specimens (almost certainly all females) have been reported, reaching between 7–8 m (22–26 ft) long with an estimated weight in excess of 300 kg (660 lb); it’s likely that the heftiest examples are either pregnant or have just consumed a large meal.

There are reports of a female green anaconda that was shot in Brazil c. 1960 that was 8.45 m (27 ft 9 in) long with a girth of 111 cm (44 in), which theoretically could have weighed between 300 and 400 kg (660–880 lb).

The latest research that determined that E. murinus actually incorporated a second species was published in the journal Diversity on 16 February 2024. The paper was authored by anaconda expert Dr Jesús A Rivas of New Mexico Highlands University (USA), in collaboration with other scientists from Universidade Estadual de Santa Cruz and Federal do Mato Grosso (both Brazil), Universidad Indoamérica (Ecuador), Universidad Mayor de San Andrés (Bolivia), Vrije Universiteit Brussel (Belgium), and the University of Queensland (Australia), as well as the Baihuaeri Waorani People of the Ecuadorian Amazon.

“Ayakima” means “The Great Snake” in the local Cariban language.

Green anacondas are distributed across northern South America and the Caribbean island of Trinidad. The two species are thought to have diverged almost 10 million years ago, and they now differ genetically by about 5.5%.

E. akayima is currently believed to be restricted to the northern Amazon/Orinoco Basin (e.g., Ecuador, Venezuela, Suriname, Guianas, Colombia and Trinidad, perhaps stretching into northern Brazil but this is as yet unconfirmed). By comparison, E. murinus is believed to occupy the southern portion of their range, e.g., including Brazil, Paraguay, Peru and Bolivia.

The longest snake species, meanwhile, is the reticulated python (Malayopython reticulatus) of south-east Asia, Indonesia and the Philippines, which regularly exceeds 6.25 m (20 ft 6 in); one giant specimen shot in Celebes (now Sulawesi), Indonesia, in 1912 was measured at 10 m (32 ft 9.5 in). Although longer than anacondas, the latter are more bulky, a characteristic perhaps enabled by the fact that they spend a lot of their time in water where their weight can be supported. They also bear live young rather than laying eggs, accounting for their greater size during pregnancy (an evolutionary feature perhaps developed to negate the risks of laying eggs in an aquatic habitat).