Reptiles: Anaconda

Range: South America Habitat: rain forests and wetlands

South America ’s green anaconda is the largest snake species in the world.

Main squeeze

The name “anaconda” actually refers to the Eunectes species of snakes, but it is most often used to refer to one species, the green (or common) anaconda Eunectes murinus. A member of the boa family, South America’s green anaconda is the heaviest snake in the world. Like its boa brethren, the anaconda kills its prey by coiling its muscular body around the creature and squeezing until the animal can no longer breathe. Jaws attached by stretchy ligaments allow the snake to swallow its prey whole, no matter the size. Anacondas can go weeks or months without eating, following a big meal.

The green anaconda is normally some shade of brownish green, olive, or grayish green and patterned with egg-shaped black spots. The Beni or Bolivan anaconda Eunectes beniensis is similar, but is found only in a small region of Bolivia. The smaller yellow anaconda Eunectes notaeus has a pattern of blotches, saddles, spots, and streaks (usually black or dark brown) against a yellow, golden tan, or greenish yellow background. The dark-spotted anaconda Eunectes deschauenseei is about the same size as the yellow anaconda and is brown with large dark spots.

Anacondas are quite at home in the water.

The water’s fine!

Anacondas like to be in or near water, and they are excellent swimmers and divers. Their eyes and nasal openings are on top of their heads, so they can wait for prey while remaining nearly hidden by the water. Anacondas rest and sun themselves in the branches of trees that hang over water along riverbanks, so the snakes can quickly dive into the water below if needed. These snakes don’t reach their massive size by eating salads: their diet consists of wild pigs, deer, birds, turtles, capybaras, caimans, and even jaguars. At the San Diego Zoo, our anacondas eat pre-killed rodents and rabbits.

The birds and the bees and the breeding ball

Anaconda courtship often lasts several weeks during the spring season. The female is thought to leave a scent trail to attract a male, but she may also produce some sort of airborne chemical signal. Researchers have observed that adult female anacondas do not move around much during the breeding season, yet males seem to flock to them from all directions. The males also constantly taste the air with their tongues to pick up a female’s scent messages. Surprisingly, anacondas sometimes cluster in a breeding ball that may have 2 to 12 males coiled around one female—and they may stay like this for up to four weeks! This breeding ball appears to be a slow-motion wrestling match among the males for an opportunity to mate. Does the strongest male win? Not necessarily! Females are usually larger and stronger and may choose which male (or males!) they prefer. Courtship frequently takes place in water.

Stretchy ligaments in the jaws allow the anaconda to swallow its prey whole.

A snake that gives birth

Like all boas, anacondas do not lay eggs; instead, they give birth to live young. The young are attached to a yolk sac and surrounded by a clear membrane, not a shell, as they develop in their mother’s body. This ensures they are kept at a fairly constant temperature and are protected from predators. When the young are ready to be born, they are pushed out an opening called the cloaca. They are still surrounded by the protective membrane and must break it open. Then they are on their own to start protecting themselves (usually by hiding at first) and to find food. The newborn anacondas are smaller versions of the adults and instinctively know how to survive on their own.

Saving their skin

Humans are the anaconda’s most dangerous predator. Green anacondas, for example, face a number of threats that could severely reduce their population. These huge snakes are hunted, both legally and illegally, in many parts of South America for their skin and for sale in the growing illegal pet trade. Local people also frequently kill anacondas, saying they are just trying to protect their livestock, pets, and families. The sad truth is that oftentimes these snakes are killed just because people fear and dislike them.