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The coypu, or nutria (Myocastor coypus), is a large, herbivorous, semiaquatic rodent and the only member of the family Myocastoridae. Originally native to temperate South America, it has since been introduced to North America, Europe, Asia, and Africa, primarily by fur ranchers. Although it is still valued for its fur in some regions, its destructive feeding and burrowing behaviors make this invasive species a pest throughout most of its range.

There are two commonly-used names in the English language for Myocastor coypus. The name nutria (or local derivatives such as "nutria- or nutra- rat") is generally used in North America and Asia; however, in Spanish-speaking countries, the word nutria refers to the otter. To avoid this ambiguity, the name coypu (derived from the Mapudungun word koypu) is used in Latin America and Europe.Carter, Jacoby. Worldwide Distribution, Spread of, and Efforts to Eradicate the Nutria (Myocastor coypus) - South America. United States Geological Survey. January 29, 2007. Retrieved on September 4, 2007. In France, the coypu is known as a ragondin. In Dutch it is known as beverrat (beaver rat). In Italy, instead, the popular name is, like in North America and Asia, nutria, but it is also called castorino (little beaver), by which its fur is known.


The coypu was first described by Juan Ignacio Molina in 1782 as Mus coypus, a member of the mouse or (tervanis) genus. The genus Myocastor, assigned in 1792 by Robert Kerr, is derived from the Greek mys and kastor, or "mouse-beaver". Geoffroy, independently of Kerr, named the species Myopotamus coypus, and it is occasionally referred to by this name.

Four subspecies are generally recognized:

M. c. bonariensis: northern Argentina, Bolivia, Paraguay, Uruguay, southern Brazil

M. c. coypus: central Chile, Bolivia

M. c. melanops: Chiloe Island

M. c. santacruzae: Patagonia

M. c. bonariensis, the subspecies present in the northernmost (subtropical) part of the coypu's range, is believed to be the type of coypu most commonly introduced to other continents.


The coypu somewhat resembles a very large rat, or a beaver with a small tail. Adults are typically in weight, and in body length, with a tail. They have a coarse, darkish brown outer fur with a soft under-fur. Two distinguishing marks are the presence of a white patch on the muzzle, and webbed hind feet. They can also be identified by their bright orange-yellow incisor teeth . The nipples of female coypu are high on her flanks. This allows their young to feed while the female is in the water.

Coypu can also be mistaken for another widely dispersed semi-aquatic rodent that occupies the same wetland habitats, the muskrat. The muskrat, however, is smaller, more tolerant of cold climates, and has a laterally flattened tail that it uses to assist in swimming, whereas the tail of a coypu is round. It can also be mistaken for a small beaver, as beavers and coypus have a very similar body design. They can be differentiated by the tail.

They are herbivorous, feeding on river plants, and live in burrows alongside stretches of water.

Commercial and environmental issues

Local extinction in their native range due to overharvest led to the development of coypu fur farms in the late 1800s and early 1900s. The first farms were in Argentina and then later in Europe, North America, and Asia. These farms have generally not been successful long term investments and farmed coypu often are released or escape as operations become unprofitable.

As demand for coypu fur declined, coypu have since become pests in many areas, destroying aquatic vegetation, irrigation systems, chewing through human-made items, such as tires and wooden house panelling in Louisiana, eroding river banks, and displacing native animals. Coypu were introduced to Louisiana in the 1930s for fur, for example, and nutria damage in Louisiana became so severe that in 2005, a bounty program was in effect to aid in controlling the animal. In the Chesapeake Bay region in Maryland, where they were introduced in the 1940s, coypu are believed to have destroyed of marshland in the Blackwater National Wildlife Refuge. In response, by 2003, a multi-million dollar eradication program was underway.

Coypu were also introduced to East Anglia, again for fur, in 1929; many escaped and damaged the drainage works, and a concerted programme by MAFF eradicated them by 1989.

Coypu meat is lean and low in cholesterol. While there have been many attempts to establish markets for coypu meat, all documented cases have generally been unsuccessful. Unscrupulous entrepreneurs have promoted coypu and coypu farms for their value as "meat", "fur", or "aquatic weed control". In recent years they have done so in countries such as the United States, China, Taiwan and Thailand. In every documented case the entrepreneurs sell coypu "breeding stock" at very high prices. Would-be coypu farmers find that the markets for their products disappear after the promoter has dropped out of the picture.

In the former Soviet republics of Central Asia, specifically Kyrgyzstan and Uzbekistan, Nutria (Russian and local languages NUTRIYA) are farmed on private plots and sold in local markets as a poor man's meat.

In addition to direct environmental damage, coypu are the host for a nematode parasite (Strongyloides myopotami) that can infect the skin of humans causing dermatitis similar to strongyloidiasis. The condition is also called "nutria itch". Bonilla et al. "Nutria Itch" in Archives of Dermatology. Vol. 136 No. 6, June 2000

Nutria and the damage they cause, in particular the damage to the levees before Hurricane Katrina, were featured in a first season episode of the A&E Television series, [[Steven Seagal: Lawman]]. Some were shot by police officers and the dead animals were fed to alligators. Seagal, who is a practicing Buddhist, says he is opposed to personally harming another creature without cause and did not actually shoot them. However, he said that he was happy that the food chain was being respected.


The distribution of coypu tends to expand and contract with successive cold or mild winters. During cold winters, coypu often suffer frostbite on their tails leading to infection or death. As a result, populations of coypu often contract and even become locally or regionally extinct as in the Scandinavian countries and states of the United States states such as Idaho, Montana and Nebraska and during the 1980s (Carter and Leonard 2002). During mild winters, their ranges tend to expand northward. For example in recent years range expansions have been noted in Washington State and Oregon (Sheffels and Sytsma 2007).


Sandro Bertolino, Aurelio Perrone, and Laura Gola "Effectiveness of coypu control in small Italian wetland areas" Wildlife Society Bulletin Volume 33, Issue 2 (June 2005) pp. 71472.

Carter, Jacoby and Billy P. Leonard: "A Review of the Literature on the Worldwide Distribution, Spread of, and Efforts to Eradicate the Coypu (Myocastor coypus)" Wildlife Society Bulletin, Vol. 30, No. 1 , pp. 162-175.

Carter, J., A.L. Foote, and L.A. Johnson-Randall. 1999. Modeling the effects of nutria (Myocastor coypus) on wetland loss. Wetlands 19(1):209-219

Lauren E. Nolfo-Clements: Seasonal variations in habitat availability, habitat selection, and movement patterns of Myocastor coypus on a subtropical freshwater floating marsh. (Dissertation) Tulane University. New Orleans. 2006. ISBN 0542609169

Sheffels, Trevor and Mark Systma. "Report on Nutria Management and Research in the Pacific Northwest" Center for Lakes and Reservoir Environmental Sciences and Resources, Portland State University. December 2007. Available on-line: http://www.clr.pdx.edu/docs/CLR_nutria_report.pdf.

External links

Mammals of Texas - Nutria

History, distribution and spread of coypu introductions worldwide; efforts to eradicate with links to other nutria sites

Louisiana Department of Wildlife and Fisheries' coypu website

National Trappers - Nutria

Nutria Recipes developed for a nutria control program

The Effect of Nutria on Marsh Loss in the Lower Eastern Shore of Maryland undated USGS report

[*] Report on coypus in the Pacific Northwest of North America.

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