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Temporal range: Late Pliocene–Recent
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Class: Mammalia
Order: Rodentia
Parvorder: Caviomorpha
Family: Myocastoridae
Genus: Myocastor
Species: M. coypus
Binomial name
Myocastor coypus
(Molina, 1782)

The coypu (from Spanish coipú, from Mapudungun kóypu;[2][3] Myocastor coypus), also known as the river rat[4] or nutria,[1][5] is a large, herbivorous, semi-aquatic rodent and the only member of the family Myocastoridae. Originally native to subtropical and temperate South America, it has since been introduced to North America, Europe, Asia, and Africa, primarily by fur ranchers.[6] 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.

Coypus live in burrows alongside stretches of water. They feed on river plant stems.[7]


Two names are commonly used in English for Myocastor coypus. The name "nutria" is generally used in North America, in Asia, and throughout countries of the former Soviet Union; however, in Spanish-speaking countries, the word "nutria" refers to the otter. To avoid this ambiguity, the name "coypu" (derived from the Mapudungun language) is used in Latin America and Europe.[8] In France, the coypu is known as a ragondin. In Dutch, it is known as beverrat (beaver rat). In German, it is known as Wasserratte (water rat). In Italy, instead, the popular name is, as in North America and Asia, "nutria", but it is also called castorino ("little beaver"), by which its fur is known in Italy. In Swedish, the animal is known as sumpbäver (marsh-/swamp beaver).

In Brazil the animal is known as ratão-do-banhado, nútria or caxingui (the latter from the Tupi language).



The coypu was first described by Juan Ignacio Molina in 1782 as Mus coypus, a member of the mouse genus.[9] The genus Myocastor, assigned in 1792 by Robert Kerr,[10] is derived from the Greek mys and kastor, or "mouse-beaver".[11] Geoffroy, independently of Kerr, named the species Myopotamus coypus,[12] and it is occasionally referred to by this name.

Four subspecies are generally recognized:[9]

  • M. c. bonariensis: northern Argentina, Bolivia, Paraguay, Uruguay, southern Brazil (RS, SC, PR, and SP)
  • M. c. coypus: central Chile, Bolivia
  • M. c. melanops: Chiloé 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.[8]


The large orange teeth are clearly visible on this coypu

The coypu somewhat resembles a very large rat, or a beaver with a small tail. Adults are typically 4–9 kg (8.8–19.8 lb) in weight, and 40–60 cm (16–24 in) in body length, with a 30- to 45-cm (12- to 18-in) tail. It is possible for coypu to weigh up to 16 to 17 kg (35 to 37 lb), although adults usually average 4.5 to 7 kg (9.9 to 15.4 lb).[13][14][15] They have coarse, darkish brown outer fur with soft dense grey under fur, also called the nutria. Three distinguishing features are a white patch on the muzzle, webbed hind feet, and large, bright orange-yellow incisors.[16] The nipples of female coypu are high on her flanks, to allow their young to feed while the female is in the water.

A coypu is often mistaken for a muskrat, another widely dispersed, semiaquatic rodent that occupies the same wetland habitats. The muskrat, however, is smaller and more tolerant of cold climates, and has a laterally flattened tail 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 very similar anatomies. However, beavers' tails are flat and paddle-like, as opposed to the round tails of coypus.

Life history

Coypu behaviours
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Coypus can live up to six years in captivity, but individuals uncommonly live past three years old; according to one study, 80% of coypus die within the first year, and less than 15% of a wild population is over three years old.[17] Male coypus reach sexual maturity as early as four months, and females as early as three months; however, both can have a prolonged adolescence, up to the age of 9 months.[18] Once a female is pregnant, gestation lasts 130 days, and she may give birth to as few as one or as many as 13 offspring. Baby coypus are born fully furred and with open eyes; they can eat vegetation with their parents within hours of birth. A female coypu can become pregnant again the day after she gives birth to her young.[18] If timed properly, a female can become pregnant three times within a year. Newborn coypus nurse for seven to eight weeks, after which they leave their mothers.[18]

Besides breeding quickly, each coypu consumes large amounts of vegetation. An individual consumes about 25% of its body weight daily, and feeds year-round.[18][19] Being one of the world's larger extant rodents, a mature, healthy coypu averages 5.4 kg (12 lb) in weight, but they can reach as much as 10 kg (22 lb).[20][21] They eat the base of the above-ground stems of plants, and often will dig through the organic soil for roots and rhizomes to eat.[22] Their creation of "eat-outs", areas where a majority of the above- and below-ground biomass has been removed, produces patches in the environment, which in turn disrupts the habitat for other animals and humans dependent on marshes.[23]

Coypus are found most commonly in freshwater marshes, but also inhabit brackish marshes and rarely salt marshes.[24][25]

Commercial and environmental issues

Myocastor coypus
Coypu with pale fur

Local extinction in their native range due to overharvesting led to the development of coypu fur farms in the late 19th and early 20th centuries. 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. The first attempt at coypu farming was in France in the early 1880s, but it was not much of a success.[26] The first efficient and extensive coypu farms were located in South America in the 1920s.[26] The South American farms were very successful, and led to the growth of similar farms in North America and Europe. Coypus from these farms often escaped, or were deliberately released into the wild to provide a game animal or to remove aquatic vegetation.[27]

Coypus were introduced to the Louisiana ecosystem in the 1930s, when they escaped from fur farms that had imported them from South America. Nutria first came to Louisiana from South America in 1937, when E. A. McIlhenny brought 13 of them to Avery Island. [28] In 1940, some of the nutria escaped during a hurricane and quickly populated coastal marshes, inland swamps and other wetland areas.[29] From Louisiana, coypus have spread across the Southern United States, wreaking havoc on marshland.

As demand for coypu fur declined, coypu have since become pests in many areas, destroying aquatic vegetation, marshes, and irrigation systems, and chewing through human-made items, such as tires and wooden house panelling in Louisiana, eroding river banks, and displacing native animals. Damage in Louisiana has been sufficiently severe since the 1950s to warrant legislative attention; in 1958, the first bounty was placed on nutria, though this effort was not funded.[30]:3 By the early 2000s, the Coastwide Nutria Control Program (CNCP) was established, which began paying bounties for nutria killed in 2002.[30]:19–20 In the Chesapeake Bay region in Maryland, where they were introduced in the 1940s, coypus are believed to have destroyed 7,000 to 8,000 acres (2,800 to 3,200 ha) of marshland in the Blackwater National Wildlife Refuge. In response, by 2003, a multimillion-dollar eradication program was underway.[31]

In the United Kingdom, coypus were introduced to East Anglia, for fur, in 1929; many escaped and damaged the drainage works, and a concerted programme by MAFF eradicated them by 1989.[32] However, in 2012, a "giant rat" was killed in County Durham, with authorities suspecting the animal was, in fact, a coypu.[33]

Coypu meat is lean and low in cholesterol. While many attempts have been made to establish markets for coypu meat, most 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 the markets for their products disappear after the promoter has left.[citation needed] Marsh Dog, a Baton Rouge, Louisiana based company, received a grant from the Barataria-Terrebonne National Estuary Program [34] to establish a company that uses nutria meat for dog food products. In 2012 the Louisiana Wildlife Federation recognized Marsh Dog with "Business Conservationist of the Year" award for finding a use for this eco-sustainable protein. [35]

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

In addition to direct environmental damage, coypus are the host for a nematode parasite (Strongyloides myopotami) that can infect the skin of humans, causing dermatitis similar to strongyloidiasis.[36] The condition is also called "nutria itch".[37]


The distribution of coypus tends to contract or expand with successive cold or mild winters. During cold winters, coypus often suffer frostbite on their tails, leading to infection or death. As a result, populations of coypus often contract and even become locally or regionally extinct as in the Scandinavian countries and such US states as Idaho, Montana, and Nebraska during the 1980s.[38] During mild winters, their ranges tend to expand northward. For example, in recent years, range expansions have been noted in Washington and Oregon,[39] as well as Delaware.[40]

According to the U.S. Geological Survey, nutria were first introduced the United States in California, in 1899. They were first brought to Louisiana in the early 1930s for the fur industry, and the population was kept in check, or at a small population size, because of trapping pressure from the fur traders.[41] The earliest account of nutria spreading freely into Louisiana wetlands from their enclosures was in the early 1940s; a hurricane hit the Louisiana coast for which many people were unprepared, and the storm destroyed the enclosures, enabling the nutria to escape into the wild.[41] According to the Louisiana Dept. of Wildlife and Fisheries, nutria were also transplanted from Port Arthur, Texas, to the Mississippi River in 1941 and then spread due to a hurricane later that year.[42]

Herbivory damage to wetlands

A coypu on logs.

Wetlands in general are a valuable resource both economically and environmentally. For instance, the U.S. Fish and Wildlife Service determined wetlands covered only 5% of the land surface of the contiguous 48 United States, but they support 31% of the nation's plant species.[43] These very biodiverse systems provide resources, shelter, nesting sites, and resting sites (particularly Louisiana’s coastal wetlands such as Grand Isle for migratory birds) to a wide array of wildlife. Human users also receive many benefits from wetlands, such as cleaner water, storm surge protection, oil and gas resources (especially on the Gulf Coast), reduced flooding, and chemical and biological waste reduction, to name a few.[43] In Louisiana, rapid wetland loss occurs due to a variety of reasons; this state loses an estimated area about the size of a football field every hour.[44]

In 1998, the Louisiana Department of Wildlife and Fisheries (LDWF) conducted the first Louisiana coast-wide survey, which was funded by the Coastal Wetlands Planning, Protection, and Restoration Act and titled the Nutria Harvest and Wetland Demonstration Program, to evaluate the condition of the marshlands.[45] The survey revealed through aerial surveys of transects that herbivory damage to wetlands totaled roughly 90,000 acres. The next year, LDWF performed the same survey and found the area damaged by herbivory increased to about 105,000 acres.[24] The LDWF has determined the wetlands affected by nutria decreased from an estimated 80,000+ acres of Louisiana wetlands in 2002-2003 season to about 6,296 acres during the 2010-2011 season.[46] The LDWF stresses that coastal wetland restoration projects will be greatly hindered without effective, sustainable nutria population control.

Nutria herbivory "severely reduces overall wetland biomass and can lead to the conversion of wetland to open water.[19] " Unlike other common disturbances in marshlands, such as fire and tropical storms, which are a once- or few-times-a-year occurrence, nutria feed year round, so their effects on the marsh are constant. Also, nutria are typically more destructive in the winter than in the growing season, due largely to the scarcity of above-ground vegetation; as nutria search of food, they dig up root networks and rhizomes for food.[22] While nutria are the most common herbivores in Louisiana marshes, they are not the only ones. Feral hogs, also known as wild boars (Sus scrofa), swamp rabbits (Sylvilagus aquaticus), and muskrats (Ondatra zibethicus) are less common, but feral hogs are increasing in number in Louisiana wetlands. On plots open to nutria herbivory, 40% less vegetation was found than in plots guarded against nutria by fences. This number may seem insignificant, and indeed herbivory alone is not a serious cause of land loss, but when herbivory was combined with an additional disturbance, such as fire, single vegetation removal, or double vegetation removal to simulate a tropical storm, the effect of the disturbances on the vegetation were greatly amplified.[19] " Essentially, this means, as different factors were added together, the result was less overall vegetation. Adding fertilizer to open plots did not promote plant growth; instead, nutria fed more in the fertilized areas. Increasing fertilizer inputs in marshes will only increase nutria biomass instead of the intended vegetation, therefore increasing nutrient input is not recommended.[19]

Control efforts

A trap for capturing nutria

Nutria herbivory "is perhaps the least studied or quantified aspect of wetland loss.[45] " Many coastal restoration projects involve planting vegetation to stabilize marshland, but if nutria are in the area, then without proper nutria control, all the money and effort put into restoration would be pointless. In the USA, the most recent program instituted to provide incentives for harvesting nutria is the Coastwide Nutria Control Program; it has proven to be the most successful in minimizing the nutria population. Starting in 2002, LDWF has performed aerial surveys just as they had done for the Nutria Harvest and Wetland Demonstration Program (mentioned previously), only it is now under a different program title. Under the Coastwide Nutria Control Program, which also receives funds from CWPPRA, 308,160 nutria were harvested the first year (2002–2003), revealing 82,080 acres damaged and totaling $1,232,640 in incentive payments paid out to those legally participating in the program.[46] Essentially, once a person receives a license to hunt or trap nutria, then that person is able to capture an unlimited number. When a nutria is captured, the tail is cut off and turned it in to a Coastal Environments Inc. official at an approved site. Each nutria tail is worth $5, which is an increase from $4 before the 2006-2007 season. Nutria harvesting increased drastically during the 2009-2010 year, with 445,963 nutria tails turned in worth $2,229,815 in incentive payments.[46] Each CEI official keeps record of how many tails have been turned in by each individual per parish, the method used in capture of the nutria, and the location of capture. All of this information is transferred to a database to calculate the density of nutria across the Louisiana coast, and the LDWF combines these data with the results from the aerial surveys to determine the number of nutria remaining in the marshes and the amount of damage they are inflicting on the ecosystem.[46]

Another program executed by LDWF involves creating a market of nutria meat for human consumption, though it is still trying to gain public notice. Nutria is a very lean, protein-rich meat,[47] low in fat and cholesterol with the taste, texture, and appearance of rabbit or dark turkey meat.[25] Few pathogens are associated with the meat, but proper heating when cooking should kill them. The quality of the meat and the minimal harmful microorganisms associated with it make nutria meat an "excellent food product for export markets".[25]

Several desirable control methods are currently ineffective for various reasons. Zinc phosphide is the only rodenticide currently registered to control nutria, but it is expensive, remains toxic for months, detoxifies in high humidity and rain, and requires construction of floating rafts (expensive) for placement of the chemical. It is not yet sure how many nontarget species are susceptible to zinc phosphide, but birds and rabbits have been known to die from ingestion.[48] Therefore, this chemical is rarely used, especially not in large-scale projects. Other potential chemicals would be required by the US Environmental Protection Agency to undergo vigorous testing before it would be acceptable to use on nutria. The LDWF has estimated costs for new chemicals to be $300,000 for laboratory, chemistry, and field studies, and $500,000 for a mandatory Environmental Impact Statement.[48] Contraception is not a common form of control, but is preferred by some wildlife managers. It also is expensive to operate - an estimated $6 million annually to drop bait laced with birth control chemicals. Testing of other potential contraceptives would take about five to eight years and $10 million, with no guarantee of FDA approval.[48] Also, an intensive environmental assessment would have to be completed to confirm or deny that any nontarget organisms were affected by the contraception chemicals. Neither of these control methods is likely to be used in the near future.[citation needed]

Coypus are classed as a "prohibited new organism" under New Zealand's Hazardous Substances and New Organisms Act 1996, preventing it from being imported into the country.[49] In the United States, an eradication program on the Delmarva Peninsula, between Chesapeake Bay and the Atlantic coast, where they once numbered in the tens of thousands and had destroyed thousands of acres of marshland, had nearly succeeded by 2012.[50]



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Further reading

  • 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. 714–72.
  • 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 (Spring, 2002), 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 0-542-60916-9
  • 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: [1]

External links