Common name: Green Anaconda
available through www.itis.gov
Identification: The green anaconda is the largest snake in the world. Its solid, heavy body is olive-green to brown and patterned with numerous circular black markings scattered along its length. The scales are smooth and glossy (Areste and Cebrian 2003, Mattison 2006). This particular pattern and coloration provides the snake with camouflage while it lies submerges among aquatic vegetation. These snakes also exhibit the greatest sexual size dimorphism of any terrestrial vertebrate. Breeding females are at least five times the size of breeding males (Rivas 2000).
Size: Large females can reach total lengths up to 26 ft (8m)
Native Range: Green Anacondas are found throughout tropical South America, east of the Andes, mainly in the Amazon and Orinoco basins and in the Guianas, as well as the island of Trinidad (Areste and Cebrian 2003; Mattison 2006; Reed and Rodda, 2009).
Hydrologic Unit Codes (HUCs) Explained
Puerto Rico &
Interactive maps: Point Distribution Maps
Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Eunectes murinus are found here.
Table last updated 12/10/2023
† Populations may not be currently present.
Ecology: The Green Anaconda is an aquatic snake usually found submerged under the water or near the water’s edge. It can be found in deep, shallow, turbid, and clear waters, and lacustrine and riverine habitats. It often is found in seasonally flooded areas (Reed and Rodda, 2009). Because of its aquatic nature, it is able to escape extremes in temperature variation.
This species is a constrictor, nonvenomous, and an ambush predator. It immobilizes and kills its prey by using its jaws to hold on the prey while coiling its body around the animal and constricting until it dies from suffocation or other crushing injuries. The list of potential prey items of an anaconda is extensive and varied, and consists of birds, amphibians, reptiles, mammals, and fish. Small individuals may climb trees to raid bird nests. The Green Anaconda swallows its prey whole, even prey much larger than the diameter of their mouths. They are known to consume large prey such as peccaries, capybaras, tapirs, deer, and sheep. This species has a slow-acting digestive system; it often takes days or weeks to digest food. After a meal, an anaconda may not eat for weeks or months (Reed and Rodda, 2009). There are few records of attacks on humans, and no well-documented deaths (Rivas, 1998; Reed and Rodda, 2009).
Anacondas are not immune from predators. Neonates and juveniles are particularly prone to predation, and seem to suffer high mortality within their first year. Predators of small anacondas include Crab-eating Foxes, tegu lizards, Crested Caracaras, caimans, and larger Green Anacondas (Rivas et al. 1999; Rivas et al. 2001; Mattison, 2006).
The Green Anaconda reproduces sexually and has internal fertilization. Courtship often extends over several months and the mating period typically is from April to May. The female is thought to lay down a pheromone trail, which attracts the male. Often the snakes cluster in a breeding ball which may consist of up to 13 males coiled around one female. The gestation period for the Green Anaconda is 6 to 10 months. This species gives birth to live young. A female anaconda can give birth to as many as a 82 young, though typically the size of the litter ranges from 28 to 42 (Reed and Rodda, 2009).
Means of Introduction: Probable pet release or escape.
Status: Reed and Rodda (2009) cited a personal communication that, in addition to one confirmed Green Anaconda being found dead on the road in the Fakahatchee Strand area in 2004, two other medium-sized adults and one juvenile had been observed in the same area. Based on this information, Krysko et al. (2011) suggested that since Green Anacondas are cryptic and aquatic, a population in the Fakahatchee Strand area could be established; however, no Green Anacondas have been confirmed in the area since the 2004 individual was found.
Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.
References: (click for full references)
Areste, M. and R. Cebrian. 2003. Snakes of the World. Sterling Publishing Co., Inc. New York 256 pp.
Krysko, K.L., J.P. Burgess, M.R. Rochford, C.R. Gillette, D. Cueva, K.M. Enge, L.A. Somma, J.L. Stabile, D.C. Smith, J.A. Wasilewski, G.N. Kieckhefer, III, M.C. Granatosky, and S.V. Nielsen. 2011. Verified non-indigenous amphibians and reptiles in Florida from 1863 through 2010: Outlining the invasion process and identifying invasion pathways and stages. Zootaxa 3028:1-64.
Mattison, C. 1986. Snakes of the World. Facts on File Publications. New York, New York. 190 pp.
Mattison, C. 2006. Snake. D.K. Publishing, Inc. New York. 192pp.
Reed, R.N., and Rodda, G.H. 2009. Giant constrictors: biological and management profiles and an establishment risk assessment for nine large species of pythons, anacondas, and the boa constrictor: U.S. Geological Survey Open-File Report 2009–1202, 302 p. (Also available at http://pubs.usgs.gov/of/2009/1202/pdf/OF09-1202.pdf.)
Rivas, J. A. 1998. Iguana iguana (Green Iguana): Juvenile predation. Herpetological Review 29(4): 238-239.
Rivas, J.A., 1998, Predatory attacks of green anacondas (Eunectes murinus) on adult human beings: Herpetological Natural History 6:157—159.
Rivas, J. A., J. B. Thorbjarnarson, M. C. Munoz and R. Y. Owens. 1999. Eunectes murinus: Caiman predation. Herpetological Review 30(2): 101.
Rivas, J. A. 2000. Life history of the green anaconda (Eunectes murinus) with emphasis on its reproductive biology. Ph.D. thesis, University of Tennessee, Knoxville.
Rivas, J.A., Thorbjarnarson, J.B., Munoz, M.C., and Owens, R.Y. 1999. Eunectes murinus: caiman predation. Herpetological Review 30(2):101.
Rivas, J. A. and R. Y. Owens. 2000. Eunectes murinus (Green anaconda): Cannibalism. Herpetological Review 31(1): 45-46.
Rivas, J. A., R. Y. Owens and P. P. Calle. 2001. Eunectes murinus: Juvenile predation. Herpetological Review 32 (2): 107-108.
Pam Fuller, and Denise R. Gregoire
Revision Date: 7/31/2023
Pam Fuller, and Denise R. Gregoire, 2023, Eunectes murinus (Linnaeus, 1758): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=2636, Revision Date: 7/31/2023, Access Date: 12/10/2023
This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.