Green Anaconda

Green anacondas are ambush predators. They lie nearly submerged with eyes and nostrils above the surface, then strike, coil around prey, and constrict until it suffocates. Curved teeth hold the animal, and prey is swallowed headfirst. Death comes from respiratory and circulatory failure, and drowning is common. Flexible jaw ligaments let them swallow prey wider than their head. Adults take prey equal to 14 to 50 percent of their own body mass, including capybaras, caimans, collared peccaries, turtles, and birds. Juveniles start smaller, eating birds and young caimans weighing about 40 to 70 g (1.4 to 2.5 oz). Hunters detect prey through scent, vibrations, and heat-sensing pit organs on the upper lip. After a big meal, a green anaconda can go weeks to months without eating, thanks to its low metabolism.

Green anacondas live in swamps, marshes, and slow rivers east of the Andes. They are clumsy on land but agile in water, and most active at night and around dusk. Eyes and nostrils on top of the head let them breathe and watch while the body stays hidden. Savanna populations can bury themselves in mud to wait out dry periods. When threatened, they retreat to water or mud, or coil with the head protected, and glands near the cloaca release a foul-smelling musk. They also hang from branches to dry off. Camouflage helps them blend into vegetation, and they can drop from trees onto prey. Adults face few predators: Orinoco crocodiles, black caimans, and jaguars. Juveniles and small adults die at much higher rates, and even larger anacondas may eat them.

Female green anacondas are far larger than males. Females average about 4.6 m (15 ft), often reaching 5 m (16 ft), while males average about 3 m (9.8 ft). The longest verified green anaconda measured 6.32 m (20.7 ft). Weights are less studied, but the heaviest verified wild female, at 5.21 m (17.1 ft), weighed 97.5 kg (215 lb). A captive at Pittsburgh Zoo reached 6.27 m (20.6 ft). Claims of 9 to 12 m (30 to 40 ft) lack museum specimens, and tanned skins can stretch by more than 50 percent. One researcher reports that body mass grows about 500-fold from birth to adulthood, higher than in any other snake. Wild green anacondas live about 10 years, but captives can live much longer, with the oldest on record reaching 37 years.

Mating season runs for several months, roughly March to May. Males track females by flicking their tongues to pick up pheromone trails. Up to 12 males (some sources say 13) may coil around a single female in a breeding ball that lasts 2 to 4 weeks. Males rarely fight. Instead they mainly push rivals away from the mating position, and large males may even be courted by other males who mistake them for females. Females can mate several times. After mating, larger females sometimes eat smaller males, possibly to help survive the seven-month fast of pregnancy. Males also have cloacal spurs of about 7.5 mm (0.3 in), larger than those of females. One researcher recorded 51 breeding aggregations during a long-term field study. Females breed about every other year.

Outside the breeding season, green anacondas live mostly alone. Each snake stays within its own hunting area, averaging about 0.25 sq km (0.1 sq mi) in the dry season and 0.35 sq km (0.14 sq mi) in the wet season. They move farther in dry periods and while searching for mates, usually during cooler hours. They are not inherently aggressive, but can turn aggressive when provoked, and smaller individuals tend to be more defensive. Males compete for females by coiling around them instead of fighting. Cannibalism occurs, mostly with larger females eating smaller males. They use their tongue and Jacobson’s organ to read chemical signals, and pit organs and vibration sensing help them locate neighbors and prey. They are cold-blooded and regulate temperature by basking. Vision and hearing are less developed.

Green anacondas give birth to live young. Females carry their litters for about 7 months, during which they fast and may lose up to half their body weight. Births take place in shallow water in the late afternoon or evening at the end of the wet season. Litters usually hold 20 to 40 young, with up to 82 recorded, and larger females tend to have larger litters. Each newborn weighs about 200 g (7 oz), measures roughly 70 cm (28 in), and makes up about 1 percent of its mother’s mass. There is no parental care, and females feed more heavily afterward. The young can swim and hunt almost immediately. Both sexes mature at around 3 to 4 years old, and reproduction without a male may be possible when none are present.