Although capable of moving over land, the bulky body of the adult green anaconda is best suited for life in the water, where it gracefully and stealthily seeks out prey (2) (3) (4). A variety of prey is taken according to the size of the anaconda, with smaller individuals taking fish and other small vertebrates, while larger specimens prey upon deer, capybara, and even full-grown caimans (4) (7). In addition, in rare cases this species has also been known to attack humans (8). Prey is taken by surprise, with a swift strike from the jaws, after which coils of the muscular body are quickly thrown around the animal, often dragging it underwater (4) (7). Lacking venom, the green anaconda relies on constriction to kill its prey, asphyxiating the animal, before swallowing it whole. Elastic ligaments allow the jaws to stretch widely, accommodating prey many times the width of the head and body. Large meals provide enough nourishment that the snake can go weeks or months without food (2).
Studies of the green anaconda in seasonally-flooded habitats show that it mates during the dry season, from around mid-February to late May. Males seek out a mate by following scent trails, and due to the greater numbers of males relative to females, several often converge on a single female. This leads to a phenomena known a “breeding ball”, in which the smaller males and the single, large female form a mass of writhing bodies, in which the males attempt push one another out the way in order to access the female’s cloaca and mate (5). This association can last for up to month, during which the female may mate multiple times. This mating system may help to explain the pronounced size difference between the sexes; as larger male specimens can be mistaken for females, it is disadvantageous for males to grow beyond a certain size (9). Interestingly, after mating the female may eat one or more of its mating partners. This behaviour may help it to survive pregnancy, during which food is not taken for up to seven months (10). After mating, in order to survive the dry season, green anacondas shelter underground in mud or caves formed in river banks, or they seek out deeper water (3) (11). The female typically gives birth to litters of 20 to 40 live young, though a record of 82 has been reported. The young measure around 60 centimetres in length, and take roughly six years to reach sexual maturity (2) (3) (4). From birth to adulthood, the green anaconda undergoes a dramatic 500-fold increase in mass, a greater increase than any other snake species (12). While the average lifespan is 10 years in the wild (2), individuals have been known to live for over 25 years (4).