Myocastor coypus Molina, 1782 (Nutria )


John and Karen Hollingsworth,
US Fish and Wildlife Service




Class: Mammalia

Order: Rodentia

Family: Echimyidae

Synonym(s): coypu, nutria-rat, South American beaver, Argentine beaver,and swamp beaver

Description: The nutria (Myocastor coypus) is a large, dark-colored, semiaquatic rodent. They have short legs and a robust, highly arched body that is approximately 24 inches (61 cm) long. Their round tail is 13 to 16 inches (33 to 41 cm) long and scantily haired. Males are slightly larger than females; the average weight for each is about 12 pounds (5.4 kg). Males and females may grow to 20 pounds (9.1 kg) and 18 pounds (8.2 kg), respectively. The dense grayish underfur is overlaid by long, glossy guard hairs that vary in color from dark brown to yellowish brown. The forepaws have four well developed and clawed toes and one vestigial toe. Four of the five clawed toes on the hind foot are interconnected by webbing; the fifth outer toe is free. The hind legs are much larger than the forelegs. Like beavers, nutria have large incisors that are yellow-orange to orange-red on their outer surfaces.

History: Fur ranchers imported nutria into California, Washington, Oregon, Michigan, New Mexico, Louisiana, Ohio, and Utah between 1899 and 1940. Many of the nutria from these ranches were freed into the wild when their businesses failed in the late 1940s. State and federal agencies and individuals translocated nutria into Alabama, Arkansas, Georgia, Kentucky, Maryland, Mississippi, Oklahoma, Louisiana, and Texas, with the intention to control undesirable vegetation and enhance trapping opportunities. Nutria were also sold as weed cutters to an ignorant public throughout the Southeast. A hurricane in the late 1940s aided dispersal by scattering nutria over wide areas of coastal southwest Louisiana and southeast Texas.

Biology: Nutria breed year round throughout most of their range, and sexually active individuals are present every month of the year. Under optimal conditions, nutria reach sexual maturity at 4 months of age. The gestation period for nutria ranges from 130 to 132 days and litters average 4 to 5 young, with a range of 1 to 13.

Ecological Threat: The estimated value of sugarcane and rice damaged by nutria each year has ranged from several thousand dollars to over a million dollars. If losses of other resources are added to this amount, the estimated average loss would probably exceed $1 million annually.

US Habitat: Nutria adapt to a wide variety of environmental conditions and persist in areas previously thought to be unsuitable. In the United States, farm ponds and other freshwater impoundments, drainage canals with spoil banks, rivers and bayous, freshwater and brackish marshes, swamps, and combinations of various wetland types can provide suitable habitat to nutria. Nutria habitat, in general, is the semiaquatic environment that occurs at the boundary between land and permanent water. This zone usually has an abundance of emergent aquatic vegetation, small trees, and/or shrubs and may be interspersed with small clumps and hillocks of high ground. In the United States, all significant nutria populations are in coastal areas. However, freshwater marshes are the preferred habitat.


Native Origin: South America

US States: Nutria have been reported in at least 40 states and three Canadian provinces in North America since their introduction. See USGS NAS map

Resembles/Alternatives: Beaver (Castor canadensis)
muskrat (Ondatra zibethicus)

Protect small areas with partially buried fences. Use sheet metal shields to prevent gnawing on wooden and Styrofoam structures and trees near aquatic habitat. Install bulkheads to deter burrowing into banks.

Cultural Methods and Habitat Modification
Improve drainage to destroy travel lanes. Manage vegetation to eliminate food and cover. Contour stream banks to control burrowing.

Zinc phosphide on carrot or sweet potato baits.

Double longspring traps, Nos. 11 and 2, as preferred by trappers and wildlife damage control specialists. Body-gripping traps, for example, Conibear® Nos. 160-2 and 220-2, and locking snares are most effective when set in trails, den entrances, or culverts. Live traps should be used when leghold and body-gripping traps cannot be set. Long-handled dip nets can be used to catch unwary nutria.

Effective when environmental conditions force nutria into the open. Night hunting is illegal in many states.

Text References

Carter, J., & Leonard, B. P. 2002. A review of the literature on the worldwide distribution, spread of, and efforts to eradicate the coypu (Myocastor coypus). Wildlife Society Bulletin, 162-175

Evans, J. 1970. About nutria and their control. US Dep. Inter., Bureau Sport Fish. Wildl., Resour. Publ. No. 86. 65 pp.

Evans, J. 1983. Nutria. Pages B-61 to B-70 in R.M. Timm, ed. Prevention and control of wildlife damage, Coop. Ext. Serv., Univ. Nebraska, Lincoln.

Falke, J. 1988. Controlling nutria damage. Texas An. Damage Control Serv. Leaflet 1918. 3 pp.

LeBlanc, D.J. 1994. NUTRIA. Cooperative Extension Division Institute of Agriculture and Natural Resources University of Nebraska - Lincoln.

Willner, G. R. 1982. Nutria. Pages 1059-1076 in J. A. Chapman and G. A. Feldhamer, eds. Wild Mammals of North America: Biology, Management, and Economics. The Johns Hopkins Univ. Press, Baltimore, Maryland.

Data Source

TPWD: Texas Most Unwanted Plants and Animals
Texas A&M AgriLife Extension: Managing Nutria Damage (pdf)
USDA-APHIS Wildlife Services: Nutria, An Invasive Rodent (pdf)
USGS NAS: Nutria profile and map

Last Updated: 2011-09-07 by Amber Bartelt - Sam Houston State University