Anaconda (snake)

V

Hunting and Diet

Anacondas are mainly ambush predators, similar to other constrictors. However, they are more specialized for aquatic hunting. Smell and body heat help the snakes find prey. Sounds or vibrations carried through water may also help. Eyesight is probably used only for the final up-close attack. Anacondas often swim just below the surface, hidden by vegetation before they strike. They first bite to hold the prey then throw massive coils around its body.

Anacondas use constriction to squeeze prey to death. They gradually tighten their powerful coils, preventing an animal from breathing. Recent research indicates that the enormous pressure of the coils may also stop the heart from beating, quickly cutting off circulation and the blood supply to the brain. Constriction may also snap the animal's neck or spine, and break other bones. In many cases, anacondas simply drown victims by holding them underwater. Once dead, the prey is generally swallowed headfirst.

Adult anacondas feed on a range of animals, usually caught in or near water. Mammals hunted include capybaras, deer, tapirs, peccaries, and on occasion jaguars or other cats. Domestic dogs or sheep may also fall victim to anacondas. Aquatic birds and reptiles such as caimans are also commonly preyed on. Young anacondas eat fish, frogs, and small rodents. After a large meal, anacondas may not eat again for months.

Humans are the main threat to adult anacondas, which have few predators in the wild. However, female anacondas sometimes eat male anacondas. Large caimans may eat anacondas they can overpower. Young anacondas are prey for many animals, including caimans and members of the cat family.

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VI

Humans and Anacondas

Anacondas figure prominently in the religions of native peoples of the Amazon region, often as spirits that protect forests or rivers. In some legends, giant anacondas traced out the winding courses that rivers follow.

Anacondas are not generally hunted as food, but some tribal groups use anaconda fat as a folk medicine for respiratory ailments. In some regions, anacondas are routinely killed out of fear or as potential threats to livestock. Illegal trade in skins is now the biggest threat to anaconda populations. Habitat loss is also a problem when jungle areas in parts of South America are cleared for ranching. International trade in live anacondas is possible with a permit under current Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) regulations.

Anacondas are often displayed in zoos and have been bred in captivity. However, they are rarely kept as pets. Unlike the generally docile species of pythons and boas available in the pet trade, anacondas can be aggressive and difficult to handle. When agitated, they can also give off an offensive smell from musk glands in the cloaca.

Anacondas are large enough and strong enough to overpower and kill a human with their coils. In the wild such attacks appear to be rare—more rare at least than attacks by pythons on humans. There are no authenticated cases of anacondas eating humans, although tribal peoples consider the snakes a threat to children. As with pythons, anacondas would probably have difficulty swallowing an adult human victim headfirst because of the width of the shoulders.

In the popular imagination, particular fascination centers on the maximum size anacondas can reach. The largest anaconda reported by a source considered reliable was a specimen about 11 m (37 ft) long. The snake was shot and measured by scientists, but it allegedly revived and escaped before it could be preserved for further research. The British adventurer Percy H. Fawcett claimed to have shot an anaconda over 18 m (60 ft) long, a size debated by experts. Tales of even more gigantic anacondas lack scientific evidence.

Scientific understanding of anacondas has increased considerably in recent years. Field studies of the giant snakes provide important new information. Researchers working in Venezuela have captured green anacondas and force-fed them radio transmitters, allowing the snakes to be regularly tracked for the first time to fill in many details about their behavior and diet.

Scientific classification: Anacondas belong to the family Boidae. There are four species, all in the genus Eunectes. The common anaconda is classified as Eunectes murinus, and the yellow anaconda as Eunectes notaeus. The dark-spotted or de Schauensee’s anaconda is Eunectes deschauenseei. The Bolivian anaconda is Eunectes beniensis. A species once considered separate and classified as “Eunectes barbouri” is now considered the same as Eunectes murinus.

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