nutria or coypu, aquatic rodent, Myocastor coypus, of South America, introduced in the S United States for its fur, which is similar to that of beaver but not as thick or durable. The nutria resembles a small beaver with a ratlike tail. It is up to 25 in. (64 cm) long, excluding the 15-in. (38-cm) sparsely haired, round tail; it has large reddish incisor teeth and partially webbed hind feet. The outer fur is long, coarse, and brown; it is the soft, gray undercoat that is valued commercially. Descendants of nutrias escaped from fur farms are now found in much of the United States, especially in swampy regions. They build burrows in banks, with the entrances above water level, and feed on aquatic vegetation, competing with the native muskrat for food. They have seriously damaged marshland ecosystems in southern Louisiana and, to a lesser degree, around the Chesapeake Bay. Nutrias have also established themselves successfully in Europe. They are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Capromyidae.

or coypu

Semiaquatic South American rodent (Myocastor coypus) in the hutia family (Capromyidae). The nutria has small ears, a long, rounded, scaly tail, partially webbed hind feet, and broad orange incisors. It is about 40 in. (1 m) long, including the tail, and may weigh 18 lbs (8 kg). Its reddish brown fur consists of coarse guard hairs overlying a soft undercoat. The nutria lives in a shallow burrow along a pond or river and mainly eats aquatic plants. Because their fur is valuable, nutrias were introduced into North America and Europe, and in some places have become pests that damage crops and compete with other wildlife.

Learn more about nutria with a free trial on Britannica.com.