Nutria

The coypu (also called nutria, Myocastor coypus) is a large, plant-eating, semi-aquatic rodent. It looks a bit like a very large rat, or a beaver with a small, long, skinny, hairless round tail.

Adults are typically 4-9 kg, with a body 40-60 cm long and a tail of 30-45 cm. Most average 4.5 to 7 kg, though a few can reach 16-17 kg. Three features stand out: a white patch on the muzzle, webbed hind feet and big, bright orange-yellow front teeth. They also have long whiskers and three layers of fur. Males and females look alike in colour and weight.

Nutria live in burrows beside water, mostly in freshwater marshes and wetlands, and sometimes in brackish marshes. They eat mainly aquatic and bankside plants.

Nutria are native to subtropical and temperate South America, including Chile, Argentina, Uruguay, Paraguay and southern Brazil and Bolivia. They were long placed in a family of their own, but are now grouped with the spiny rats. Their nearest relatives include the painted tree-rats.

Overharvesting caused local extinction in their native range, which led to fur farms in the late 19th and early 20th centuries. The first were in Argentina, and others followed in Europe, North America and Asia. Many farms failed, and nutria escaped or were released.

In Britain, nutria were brought to East Anglia for fur in 1929. They were reported in the wild by 1932, damaged drainage works and farmland, and were hit by several trapping campaigns. They were assumed eradicated in 1989.

Elsewhere they spread widely. Louisiana saw escapes in the 1930s and 1940s, with a hurricane helping them break out, and Japan imported them in 1939.

Nutria are mainly active at dusk and through the night, with activity peaking around midnight. When food is scarce they also feed by day, and when it is plentiful they rest and groom.

They live in colonies. One male may share a den with three or four females and their young. They build partly underwater dens, floating rafts of vegetation and feeding platforms made from cut plants.

Nutria can be territorial and aggressive when caught or cornered, and will bite people and dogs when threatened.

A nutria eats about 25% of its body weight daily, all year round. Babies are born furred with open eyes, and can eat plants and swim within hours. Females have teats high on their flanks so the young can feed while she is in the water.

Nutria can live up to six years in captivity, but rarely pass three in the wild. One study found 80% die in their first year. Four years counts as old age.

Cold winters can cause frostbite on the tail, leading to infection or death.

They can host parasites including tapeworms, liver flukes, blood flukes, fleas, ticks and lice. A roundworm they carry can cause a skin rash in people known as nutria itch.

They can also carry zoonotic germs, including salmonella and leptospirosis bacteria, though the wider significance is described as scarce and region-specific.

This is general awareness only, not veterinary advice. If you find an injured or unwell wild animal, contact a vet or a wildlife rescue.

What is a nutria?

It is a large, semi-aquatic rodent from South America, also called a coypu. It eats plants and lives in burrows by water.

How long do nutria live?

Up to about six years in captivity. In the wild they rarely pass three years.

Were there nutria in the UK?

Yes. They escaped from fur farms in East Anglia and lived wild for decades. A long trapping campaign eradicated them, and by 1989 they were assumed gone.

Is a nutria a beaver?

No, though they look alike. A nutria has a round tail, while a beaver's is flat and paddle-like.

Do nutria carry diseases?

Some can carry parasites and germs that affect people, such as salmonella and leptospirosis bacteria. Their wider significance is described as scarce and region-specific.

Are nutria active in the day?

Mostly they are active at dusk and at night. They may feed by day when food is scarce.

The genus name Myocastor means mouse-beaver, and the name nutria comes from the Spanish word for otter.

Their orange teeth get their colour from iron in the enamel, and their four large incisors never stop growing.

A female can become pregnant again the day after giving birth, and litters average four pups.

In Louisiana, hunters are paid for each tail they hand in.

In their native wetlands, one study estimated a nutria spread about 691 plant propagules a day through its droppings.