Eunectes is a genus of non-venomous boas found in tropical South America, commonly called anacondas. An aquatic group of snakes inhabiting swamps and rivers, its members include some of the largest snakes in the world. Despite this, little was known about them until recently. The name Eunectes is derived from the Greek word Eυνήκτης, which means "good swimmer." Three species are currently recognized.
The Wildlife Conservation Society has, since the early 20th century, offered a large cash reward (currently worth US$50,000) for live delivery of any snake of or more in length. This prize has never been claimed. In any case, measuring a snake that is stronger than a person is not an easy task. It was found that two scientists independently measuring the same plus snake showed a variation of more than 20% in their results.
A possible origin for the common is perhaps an alteration of the Sinhalese word henakandaya, meaning 'whip snake' or anaconda is the Tamil anaikondran, meaning "elephant killer", or anaikkonda, meaning "having killed an elephant". A name first used in English to name a Ceylonese python, it erroneously was applied to a large South American boa, called in Brazil "sucuri". The word is of uncertain origin, and no snake name like it now is found in Sinhalese or Tamil. Another suggestion is that it represents Tamil. It is unclear how this name originated so far from the snake's native habitat; possibly this is due to its vague similarity to the large Asian pythons.
The green anaconda, however, is carnivorous, and will prey on any vertebrate within reach and swallow it. It is especially interested in other snakes, amphibians, fish, and mammals such as capybara. The smaller side of the species have been known to climb trees to attack and consume bird nests, while the larger of the specimens may, and usually do, prey on small deer, caimans, and peccaries. Few records show that there have been attacks on humans. However, no known deaths have been recorded. As all other snakes do, the green anaconda swallows its victim whole and, because their jaws are unhingeable, they are able to swallow prey with a diameter larger than that of their mouths. Green anacondas usually swallow prey "head-first", from the fact that this is the usual way the limbs tend to fold over. The mouth muscles of the snake then contract in waves as swallowing process continues, crushing its prey with each surge forward. Their digestive system is slow-acting, meaning it usually takes either days or weeks to digest the food. After every meal, anacondas might not eat for a while: weeks or months.
Although it does not appear that it is necessary for there to be more than one male, quite frequently the snakes tend to grouping in a breeding ball. This breeding ball could potentially consist of up to twelve males wrapped around one female snake. The group could stay in this position from two to four weeks. This ball seems to be a type of a slow-motion wrestling match between the males; each one fighting for the right to mate with the female. The strongest and largest, of couse, often becomes victorious. However, the female anaconda, naturally physically much larger and stronger, may herself choose or deflect certain males. Courtship and copulation frequently take place in water. The gestation period for the green anaconda is about 6 months. A gravid female may feed during this period. However, males kept together during breeding season may refuse food.
The male uses its spurs to stimulate the female during mating. The male presses his cloacal region against the female while scratching her with his spurs. This makes a scratching sound. The end of the courtship comes when the stimulus of the males' spurs induces the female to raise her cloacal region, allowing the two cloacas to come together. The male wraps his tail around the female while they copulate.
This species is viviparous, giving birth to live young. A female anaconda can give birth to as many as a hundred young, though typically the size of the litter ranges from 20 to 40. The female may lose up to half of her pre-birthing weight after birth. The neonates are usually around 70-80 cm long at birth. Because of their small size they often fall prey to other animals. They grow rapidly until they reach sexual maturity in their first few years, after which their rate of growth continues at a slower pace.