Coypu: Myocastoridae

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COYPU: Myocastoridae


The coypu, sometimes called the South American beaver or nutria, looks like a muskrat, only larger. It has a stout body that is highly arched and a large, somewhat triangular head. It has small eyes and ears on the upper part of its head. Coypus have a head and body length of 1.4 to 2.1 feet (43 to 63.6 centimeters), and a tail length of 0.8 to 1.4 feet (25.5 to 42.5 centimeters. They weigh from 11 to 37 pounds (5 to 17 kilograms).

They have short, hairless legs with the hind feet longer than the front feet. Each hind foot has five toes, four of which are connected by webbing. The fifth toe is used for grooming. The front feet have four long, flexible toes without webbing, and a non-functioning thumb. Their tails are long, round, and hairless. One of the coypu's most distinguishing features is its large, wide, bright orange incisors, the flat, sharp-edged teeth at the front of the mouth used for gnawing and cutting and tearing food. They can close their lips behind the incisors, allowing them to gnaw while underwater. Their ears, nose, and nostrils are located near the top of the head so they are above water when the coypu is swimming.

Coypus have two types of hair; soft, dense under fur, and outer fur of long, course, bristly hair, called guard hair. The undercoat is dark gray and the outer coat is various shades of red, brown and yellow. The stomach fur is soft and dense and usually a pale yellow. The fur on the chin and around the nose is usually white.


The coypu is native to southern South America, from the middle of Bolivia and southern Brazil to Tierra del Fuego at the southern tip of the continent, including Argentina, Chile, Paraguay, and Uruguay. It has been introduced into North America, Europe, northern Asia, east Africa, and the Middle East where there are populations in the wild. In the United States, it is found in fifteen states coast to coast but particularly in Louisiana, Florida, Oregon, and Maryland. In Canada, it is found in British Columbia, Ontario, and Quebec. It is found throughout continental Europe, including France, Germany, Scandinavia, Austria, Russia, and Poland. Other non-native populations include those in Israel, Zimbabwe, and Japan.


Coypus adapt well to a wide range of habitats, including rainforest, deciduous forest, coniferous forest, scrub forest, grassland, wetland such as swamps and marshes, and the banks or shores of lakes, ponds, rivers, and streams.


South American coypus are omnivores, meaning they eat both plants and flesh, although they eat mostly plant material. Coypus in other parts of the world are herbivores, meaning they eat only plants. Their diet consists of a wide variety of plants and plant material, including aquatic plants such as rushes, arrowhead, smartweed, reeds, cattail, bullwhip, alligator weed, and duckweed. They also eat plant leaves, stems, roots, bark, clover, and cultivated crops such as sugarcane, sugar beets, and soybeans. On occasion, coypus in South America will eat insects, mussels, snails, mollusks, and earthworms.


Coypus are extremely passive and rarely aggressive. They are shy and fearful; the slightest disturbance will send them scurrying to the shelter of water, burrow, or other hiding places. Depending on their habitat, coypus are nocturnal, meaning they are most active at night, or crepuscular (kri-PUS-kyuh-lur), meaning they are most active at dawn and twilight.

Coypus are semi-aquatic, meaning they live both on land and in water. On land, they walk with slow, clumsy, awkward movements but if threatened, they can run fast and jump short distances. They are excellent swimmers and can remain submerged in water for more than ten minutes. Coypus can close their nostrils and lips behind their incisors while cutting vegetation under the water. The coypu is social and territorial, meaning it is protective of an area it considers home and claims exclusively for itself and its mate or family group. They live in groups of two to thirteen individuals, usually related female adults, their offspring, and one adult male. Young adult males usually live alone. Males and females have separate territories. The average home range is 6.1 acres (2.47 hectares) for females and 13.8 acres (5.68 hectares) for males.

Coypus sleep and nest in burrows, which range from a single, short tunnel, to multiple tunnels with small nesting chambers. Tunnels are often 50 feet (15 meters) or more in length. Above ground, they make raised beds of vegetation where they feed and groom.

Breeding occurs year-round and females have two or three litters per year. The gestation period, the time the females carry their young in the womb, is 127 to 139 days. The average litter size is six babies although it can range from one to thirteen. Coypus born in the summer reach sexual maturity at three to four months of age. For those born in the fall, it is reached at six or seven months of age. The average lifespan is less than one year in the wild. In a few cases under ideal conditions, coypus have lived for three to six years in the wild. However, in captivity, they can live for ten years.


In 1938, about 20 coypus were imported into Louisiana from Argentina to be bred for their fur. But many escaped captivity and adapted well to the warm, wet climate and swampy habitat, breeding voraciously. They spread quickly to nearby states. As of 2004, there were an estimated twenty million coypus in the Louisiana. In 1998, it is estimated coypus destroyed 100,000 acres of swamp and marshland, posing a serious threat to many native species of birds, mammals, and amphibians. To combat the threat to the environment, the Louisiana Department of Wildlife and Fisheries received a $10 million, five-year federal grant to help eradicate, remove, coypus from the state. In 2002, the state began paying hunters $4 for each coypu they brought into state wildlife offices. Most are brought in dead but wildlife workers kill any that are trapped and brought in alive. In the first two weeks of the program, 9,000 coypus were killed. The goal is to kill 400,000 per year.

In the wild, coypus have many predators, including large snakes like the anaconda and boa constrictor, large cats such as ocelots and jaguars, red wolves, crocodiles, and otters.


The fur of coypus is valued for its soft, velvety texture and people in South America, North America, Europe, and Japan eat the meat. Much of the meat and fur from South American comes from captive coypu breeding farms while in the United States it comes from coypus hunted in the wild, especially in Louisiana and Maryland.

In the 1930s, coypus were introduced into southeast England and the population there quickly grew. Coypus were blamed for destroying native marsh plants along riverbanks and raiding cultivated crops. Their burrows were also believed to weaken and damage river and stream banks. In the 1980s, the British government began an intensive campaign to eradicate (remove completely) coypus from England and in 1989, the government officially declared the program a total success with the killing of the last coypu.

There are eradication efforts underway in the United States, Japan, and France.


Coypus are not currently threatened, according to the World Conservation Union (IUCN). Their numbers are declining along many rivers and lakes in Argentina due to hunting and trapping by humans. The eradication efforts in the United States, France, and Japan are likely to significantly reduce populations in those areas.



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Felipe, A. E., et al. "Characterization of the Estrous Cycle of the Myocastor coypus (Coypu) by Means of Exfoliative Colpocytology." Journal of Mastozoologia Neotropical (July–December 2001): 129–137.

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Web sites:

D'Elia, Guillermo. "Myocastor coypus." Animal Diversity Web. (accessed on July 12, 2004).