September 26, 2016

Large snakes have a well-established reputation as monsters in legend and folklore throughout the world. Monstrous snakes and serpents are common themes in the myths and iconography of many ancient cultures. Because snakes are sometimes poisonous and deadly, it is only natural that many people suffer from a general fear of snakes—so many, in fact, that the fear has a name: ophidiophobia. Small and slithery and creepy snakes can make people jump, but what about the monstrous anaconda, a snake so large it can swallow a small cow?

A giant anaconda is shown to a group of tourists in Los Llanos, Venezuela. Credit: © Vadim Petrakov, Shutterstock

Anaconda is the common name of a group of large snakes found in tropical South America. Anacondas (also called water boas) have greenish, yellowish, or brownish skin, often with many black rings or spots. The green anaconda (Eunectes murinas) may grow as long as 30 feet (9 meters) and weigh nearly 450 pounds (205 kilograms). Anacondas live near water, often swimming in rivers. Their main food is fish, but they also will eat birds, small mammals, and other reptiles. Anacondas kill by wrapping their coils tightly around prey and constricting (squeezing) it to keep it from breathing and to stop its heart.

Anacondas are top predators in their habitat, and they often prey on large animals, including capybaras, white-tailed deer, and even large caimans (reptiles closely related to the alligator). Anacondas are capable of eating such large prey because the skin and ligaments around their jaws easily stretch to fit around large objects. The two sides of an anaconda’s lower jaw are also joined by an elastic ligament, creating a mobile joint that allows the snake to move and stretch its jaws well beyond the size of its own head.

Large anacondas can be dangerous to people because of their size and strength. Fortunately, anacondas live in swampy habitats where people are unlikely to encounter them. Despite sensational stories that often circulate on the Internet, there are no known instances of anacondas eating people. In fact, there are only a couple of documented anaconda attacks on humans at all. Both were attacks on researchers trying to study the gigantic snakes. Fortunately, the scientists were rescued and the anaconda’s record remained clean. Like other snakes, anacondas defend themselves from enemies by retreating or, if cornered, by biting. Their bite is not poisonous, but their many teeth can inflict deep wounds.

Feb. 6, 2012

Pythons are battling alligators for the position of top predator in Everglades National Park in Florida, and native mammals are paying the price, according to a new study by two Florida university researchers. The study is the first to provide evidence linking a sharp decline in populations of medium- and large-sized mammals in the park to an explosion in the number and range of the large snakes.

Native to Southeast Asia, the python is classified as an invasive species in North America. From 1999 to 2004, pet exporters met a growing American demand for Burmese pythons by shipping more than 144,000 baby snakes to the United States. However, new owners were frequently unprepared or unwilling to care for the grown snakes, which can measure 23 feet (7 meters) in length and weigh 200 pounds (91 kilograms). Many owners dumped their snakes into the wild. Pythons released into the Florida Everglades, a region with a climate similar to that of the snakes’ native habitat, flourished. Pythons also have escaped into the wild during hurricanes.

The study’s researchers surveyed native mammal populations over 313 nights during an eight-year period by counting live and dead animals along a road that runs to the southern tip of the park. They then compared their tallies to population surveys done in 1996 and 1997. In areas of the Everglades where pythons have lived the longest, populations of raccoons had fallen by 99.3 percent. The number of opossums had dropped by 98.9 percent, and bobcat populations had fallen by 88.5 percent. The researchers were unable to find any rabbits or foxes. Populations of native animals were larger in areas more recently or not yet invaded by the snakes.

The U.S. Association of Reptile Keepers disputed the findings of the study. The organization contended that mercury pollution in the Everglades has played a major role in the disappearance of the mammals.

Young Indian pythons hatch from eggs outside the mother's body. The leathery shells of snake eggs expand as the young snakes grow inside. When they are ready to hatch, young snakes slash their shells with a special tooth that grows on the upper jaw. AP/Wide World

Wildlife experts agree that eliminating the secretive and hard-to-hunt snakes from the park would be impossible. They are unsure if the spread of the snakes, which have no natural predators in North America, can be halted. In January, the administration of President Barack Obama outlawed the import and interstate commerce of Burmese pythons, two other pythons, and the yellow anaconda. Reptile importers are still allowed to trade in reticulated pythons and boa constrictors.

Additional World Book articles:

• Ecology
• Invasive Species (A Special Report)
• Reptile