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Eunectes murinus

Eunectes murinus, Photo: Michael Lahanas

Cladus: Eukaryota
Supergroup: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Classis: Reptilia
Subclassis: Diapsida
Infraclassis: Lepidosauromorpha
Superordo: Lepidosauria
Ordo: Squamata
Subordo: Serpentes
Infraordo: Henophidia
Superfamilia: Booidea
Familia: Boidae
Subfamilia: Boinae
Genus: Eunectes
Species: Eunectes murinus


Eunectes murinus (Linnaeus, 1758)

Type locality: "America".

Holotype: N.R.S. no. Lin. 9


* Boa murina Linnaeus 1758: 215
* Boa scytale Linnaeus 1758: 214
* Eunectes barbouri Dunn & Conant 1936

Eunectes murinus , Eunectes murinus ,


* Linnaeus, C. 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Laurentii Salvii, Holmiæ. 10th Edition: 824 pp.
* Dirksen, Lutz, and Wolfgang Böhme 2005. Studies on anacondas III. A reappraisal of Eunectes beniensis Dirksen, 2002, from Bolivia, and a key to the species of the genus Eunectes Wagler, 1830 (Serpentes: Boidae). Russian Journal of Herpetology 12 (3): 223-229.
* Dirksen, L. & W Böhme 1998. Studien an Anakondas 1: Indizien für natürliche Bastardierung zwischen der Großen Anakonda (Eunectes murinus) und der Paraguay-Anakonda (Eunectes notaeus) in Bolivien, mit Anmerkungen zur Taxonomie der Gattung Eunectes (Reptilia: Squamata: Serpentes: Boid Zool. Abh. Mus. Tierkd. Dresden, 50 (4) : 45-58.
* Eunectes murinus at the New Reptile Database. Accessed on 7 Mar 2008.

Vernacular names
Català: Anaconda comuna
English: Anaconda, Green Anaconda
Português: Sucuri verde
中文: 森蚺


Eunectes murinus (derived from the Greek "Ευνήκτης" meaning "good swimmer" and the Latin "murinus" translated into "he who predates on mice") is a non-venomous boa species found in South America. It is the most massive of all known snake species. Two subspecies are currently recognized, including the nominate subspecies described here.[2] The term "anaconda" (without any further description) often refers to this species, though the term could also apply to other members of the genus.


The Green Anaconda is one of the world's longest snakes, reaching more than 5 m (17 ft) long. Reports of anacondas 35–40 feet or even longer also exist but such claims need to be regarded with caution as no specimens of such lengths have ever been deposited in a museum and hard evidence is required.[3] There is a $50,000 cash reward for anyone that can catch an anaconda 30 feet or longer, but the prize has not been claimed yet.[4] Although the reticulated python is longer, the anaconda is the heaviest snake. The longest (and heaviest) scientifically recorded specimen was a female measuring 521 cm (18.1 ft) in length and weighing 97.5 kg (214 lbs).[5]

The color pattern consists of olive green background overlaid with black blotches along the length of the body. The head is narrow compared to the body, usually with distinctive orange-yellow striping on either side. The eyes are set high on the head, allowing the snake to see out of the water while swimming without exposing its body.

Maximum size

The green anaconda is among the longest and most massive snakes in the world, along with the reticulated python Python reticulatus. However, as it has inspired many wild tales of snakes ranging from large to impossibly huge, the true maximum size of this snake has remained the subject of much dispute.

Difficulties in determining maximal size

The remote location of the snake's habitat has historically made locating, capturing, and returning specimens difficult. Transporting very large specimens to museums, especially before substantial decay, is difficult (though it should be noted that this has not prevented the return of much larger and more cumbersome crocodilian specimens).[3] Skins can stretch substantially, increasing the snake's size by more than 50% if stretched during the tanning process. Reports without physical proof are considered dubious if from non-scientists, as such individuals may at worst be more interested in promoting themselves or telling a good tale, or at the least may not be sufficiently trained in proper measurement methods. Observational reports of animals which were not captured are even more dubious, as even trained scientists often substantially overestimate the size of anacondas prior to capture.[3]

Historical Records

There are numerous historical accounts of green anacondas, often of ridiculously improbable sizes. Several zoologists (notably Henry Walter Bates and Alfred Russel Wallace, among others) note rumors of snakes beyond 30 or 40 feet long, but in each case note that their direct observations were limited to snakes of approximately 20 feet in length. Numerous estimates and second-hand accounts abound, but are generally considered unreliable. In one of the most reliable accounts, a geologist killed a large anaconda and measured it using a 4-meter rod, reporting it as 3 rods long (12 meters), however the information was not published until many years later, and the geologist later suggested he may have mis-remembered and the anaconda was only 2 rods long (8 meters).

Current estimates of maximal size

Peter Pritchard considered the statistical aspects of green anaconda size, along with many other snakes of all size ranges. In many cases, maximal size was between 1.5 to 2.5 times the minimal adult length. Based on this and an estimate of 3.2 meters (10.5 feet) for minimum adult size of the green anaconda, the largest snake expected would be 8 meters long (26.3 feet). However, in the case of the reticulated python, a captive adult female was reported to have exceeded the 2.5x rule, so it should be regarded as an estimate. Furthermore, it has been suggested that most anacondas are captured from the llanos, which is more accessible to humans and has smaller prey available, while the rainforest, which is less explored and has more plentiful large prey, may be home to larger snakes.

Common names

Green Anaconda, Anaconda, Common Anaconda, Water Boa.[6]

Local names in South America include the Spanish term "mata-toro", meaning "bull killer", and the Native American terms sucuri tupi-guarani and "yaqumama" in the Peruvian Amazon, which means "mother of the water" in the Quechua language of the jungle people Yaqurunas or "water people". In Trinidad, it has been traditionally referred to as the huille or huilla (pronounced whee-yay or whee-ya, respectively).

Geographic range

Found in South America in countries east of the Andes, including Colombia, Venezuela, the Guianas, Ecuador, Peru, Bolivia, Brazil, the island of Trinidad and as far south as northern Paraguay[7]. The type locality given is "America".[1] A small sub-population has been recorded in the Florida Everglades and this population is considered invasive. [1] In 2010, the state of Florida issued hunting licenses in a move to exterminate large non-native snakes recognized as a threat to the ecosystem, the green anaconda among them. [2]

Anacondas live in swamps, marshes, and slow-moving streams, mainly in the tropical rain forests of the Amazon and Orinoco basins. They are cumbersome on land, but stealthy and sleek in the water. Their eyes and nasal openings are on top of their heads, allowing them to lay in wait for prey while remaining nearly completely submerged.[3]
[edit] Behavior

The primarily nocturnal anaconda species tend to spend most of its life in or around water. Anacondas are also sometimes known as the "Water Boa"; they spend more time in water than any of the boas. Because of their large size, they appear rather slow and sluggish when traveling on land. Completely the opposite in water, however, anacondas are known to have the potential to reach high speeds in all depths of water. They tend to float atop the surface of the water with the snout barely poking out above the surface. When prey passes by or stops to drink, a hungry anaconda will snatch it with its jaws (without eating or swallowing it) and coil around it with its body. The snake will then constrict until it has successfully suffocated the prey.[8]


Primarily aquatic, they eat a wide variety of prey, almost anything they can manage to overpower, including fish, birds, a variety of mammals, and other reptiles. Particularly large anacondas may even consume large prey such as tapir, deer, capybara and caiman, but such large meals are not regularly consumed. There are many local stories and legends regarding the anaconda as a man-eater, but there is very little evidence to support any such activity. They employ constriction to subdue their prey. Cannibalism among green anacondas is also known, most recorded cases involving a larger female consuming a smaller male. Scientists cite several possible reasons for this, including the dramatic sexual dimorphism in the species and the possibility that female anacondas require additional food intake after breeding to sustain their long gestation period and the male simply being an opportunistic carnivore item, but the exact reason is not understood.[9]


This species is solitary until the mating season, which occurs during the rainy season, and can last for several months, usually from April to May. During this time, males must find females. Typically, female snakes will lay down a trail of pheromones for the males to follow, but it is still unclear how the males of this species track a female's scent. Another possibility is that the female releases an airborne stimulant. This theory is supported by the observation of females that remain motionless while many males move towards them from all directions. Male anacondas also frequently flick their tongues to sense chemicals that signal the presence of the female.[10]

In any case, many males often find the same female. Although it may not be necessary for there to be more than one male, this results in odd clusters, referred to as "breeding balls," in which up to 12 males wrap around the same female and attempt to copulate. The group could stay in this position from 2–4 weeks. This ball acts as a slow-motion wrestling match between the males, each one fighting for the right to mate with the female.

During mating, males make use of their spurs to arouse the female. They aggressively press their cloacal regions hard against the female body while continuously scratching her with their spurs. This can produce a scratching sound. Mating approaches its climax when the stimulus of the males' spurs induce the female snake to raise her cloacal region, allowing the cloacae of the two snakes to move together. The male then coils his tail, surrounding the female and they copulate.[11] The strongest and largest male is often the victor. However, females are physically much larger and stronger and may decide to choose from among the males. Courtship and mating occur almost exclusively in water. The female anaconda is covered or surrounded by many male anacondas to reproduce.

Mating is followed by a gestation period that lasts approximately 6–7 months. The species is ovoviviparous, with females giving birth to live young. Litters usually consists of 20–40 offspring, although as many as 100 may be produced. After giving birth, females may lose up to half their weight.

Neonates are around 70–80 cm long and receive no parental care. Because of their small size, they often fall prey to other animals. Should they survive, they grow rapidly until they reach sexual maturity in their first few years, after which their rate of growth continues at a slower pace.[12]


Anacondas, like other snakes and most other reptiles, can quite easily adapt to a change in the climate, environment, and near surroundings when necessary. The reasons for an anaconda's needing to adapt can vary. They may need to adapt to adjust to changes in the availability of food, and any diseases they may be exposed to in new surroundings. An anaconda might also have to adjust to changes in temperature and humidity. Changes in temperature could drastically affect the snake because it is ectothermal, and relies on its environment to control its temperature. If the temperature of its surroundings increases, a snake will do everything possible to prevent its body from over-heating, and if it decreases, it will attempt to lie in heated areas to help maintain its normal temperature. Anacondas, like all other snakes, control and regulate their body temperatures by changing the amount of surface of their skin that is exposed to the sun. If the terrarium, location or "tank" where a reptile is kept, is uniformly heated producing what is known as "the greenhouse effect", then the snake could possibly die from over-heating (hyperthermia). The humidity of its surroundings might also be slightly different than the humidity to which the snake was previously accustomed. This could, potentially, drastically alter its shedding cycle. The obstruction of this cycle is extremely dangerous. The hindrance of an anaconda's shedding cycle most often causes retention of eye caps.[13] Due to these conditions and emotions of the snake, anacondas are known for their aggressive disposition when being held in captivity.[14]

Environmental requirements

One may reasonably maintain an average and acceptable temperature for the snake by the use of a simple heater and infrared light bulbs. Anacondas and other snakes must be exposed to ultraviolet (UV) radiation. This is exceptionally significant because the snake needs it to produce vitamin D3 for further bone development in its body. Occasional exposure to light bulbs that emit UV radiation with proper wavelength, or better yet, the sun, is also necessary to maintain the positive health of an anaconda. Optimum humidity can be difficult to maintain and research must be done on the snake to determine the correct level. A percentage of just less than 80% humidity must be maintained for caging an anaconda species from the tropical region, while a slightly less than 30% humidity must be maintained for a species of a desert region.[13]

Subspecies[2] Taxon author[2] Common name Geographic range
E. m. gigas (Latreille, 1801)
E. m. murinus (Linnaeus, 1758)


Anacondas have been portrayed in horror literature and film, often with the ability to swallow adult humans; these traits are occasionally also attributed to other species, such as the Burmese python and the boa constrictor. Among the most popular films that feature it are the 1997 film, Anaconda, along with its three sequels Anacondas: The Hunt for the Blood Orchid, Anaconda 3: Offspring and Anacondas: Trail of Blood. This species is also the main antagonist in Mathias Bradley's novel, Anacondas: The Terror of the Amazon Rainforest, in which multiple hybrid anacondas escape from a research facility in the Amazon Rainforest and come into contact with a toxic chemical that causes them to rapidly mutate into gigantic snakes. A more positive depiction of the anaconda exists in the short stories "Anaconda" and "El Regreso de Anaconda" ("The Return of Anaconda") by Horacio Quiroga, which are told from the anaconda's point of view.


1. ^ a b McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. ISBN 1-893777-00-6 (series). ISBN 1-893777-01-4 (volume).
2. ^ a b c "Eunectes murinus". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=634802. Retrieved 3 July 2008.
3. ^ a b c Murphy JC, Henderson RW. 1997. Tales of Giant Snakes: A Historical Natural History of Anacondas and Pythons. Krieger Pub. Co. 221 pp. ISBN 0894649957.
4. ^ Rivas JA, Ascanio RE, Muñoz MDC. 2008. What is the length of a snake? Comtemporary Herpetology, Vol. 2008(2):1-3. PDF at Comtemporary Herpetology. Accessed 18 July 2008.
5. ^ Rivas, Jesús A. 2000. The life history of the green anaconda (Eunectes murinus). With emphasis on its reproductive Biology. Dissertation. University of Tennessee. PDF Accessed 10 May 2009.
6. ^ Mehrtens JM. 1987. Living Snakes of the World in Color. New York: Sterling Publishers. 480 pp. ISBN 0-8069-6460-X.
7. ^ Seven-meter-long, 90 kg anaconda "fished" In Spanish. ABC Color, 4 January 2008.
8. ^ Soomro, Adil (April 2001). "Animal Diversity Web". University of Michigan Museum of Zoology. University of Michigan Museum of Zoology. http://animaldiversity.ummz.umich.edu/site/accounts/information/Eunectes_murinus.html. Retrieved 2008-11-12.
9. ^ Eunectes murinus (Green Anaconda): Cannibalism at Prodigy. Accessed 3 July 2008.
10. ^ Burton, Maurice and Robert Burton. International Wildlife Encyclopedia, pg. 44.
11. ^ Herpetologist Jesus Rivas
12. ^ Soomro, Adil (2001). "Eunectes murinus". The University of Michigan Museum of Zoology (Animal Diversity Web). http://animaldiversity.ummz.umich.edu/site/accounts/information/Eunectes_murinus.html. Retrieved 2008-10-10.
13. ^ a b E. Fowler, Murray; Zalmir S. Cubas (2001). Biology, Medicine, and Surgery of South American Wild Animals. Blackwell Publishing. pp. 40–41. ISBN 0813828465. 14. ^ LLLReptile: Green Anaconda Captive Care at LLLReptile. Accessed 3 July 2008.

Further reading

* Dirksen L, Böhme W. 1998. Studien an Anakondas 2: Zum taxonomischen Status von Eunectes murinus gigas (Latreille, 1801) (Serpentes: Boidae), mit neuen Ergebnissen zur Gattung Eunectes Wagler, 1830.- Salamandra 34(4): 359-374.
* Dirksen L. 2002. Anakondas. Monographische Revision der Gattung Eunectes (Wagler, 1830).- Natur und Tier-Verlag Münster. ISBN 3-931587-43-6. 187 pp.

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