Disclaimer:

The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

---

Common name: nutria

Taxonomy: available through www.itis.gov

Identification: Nutria (Myocastor coypus) are large, semi-aquatic rodents that have robust, highly arched bodies with short legs, and long tails. Their body is covered in dense fur that ranges in color from light to dark brown, except on the tail where hair is sparse. Their head is large and nearly triangular with small ears, a tapering nose with long vibrissae (whiskers), and prominent incisors. The first four toes of the hind feet are webbed for swimming, while the fifth digit is free and used for grooming (Lowery 1974; Woods et al. 1992; LeBlanc 1994; California Department of Fish and Wildlife 2021). The eyes, ears, and nostrils of M. coypus are all located superiorly (towards the top) on the cranium, reflecting their aquatic life history (Evans 1970; Woods et al. 1992; LeBlanc 1994).

Myocastor coypus strongly resemble American Beavers (Castor canadensis) and Muskrats (Ondatra zibethicus) (Evans 1970; LeBlanc 1994; California Department of Fish and Wildlife 2021); however, they are distinguished from these native species through examination of several physical features. The most conspicuous identifying features of M. coypus are their white whiskers, and large, rounded tail. The tail differs from Beavers, which have broad, flat tails that are compressed dorsoventrally (flattened top-to-bottom), and Muskrats that have short, laterally compressed (flattened side-to-side) tails. The body size of these species also differs considerably. Adult Beavers reach a larger size than M. coypus, growing to about 18 kilograms (kg) (40 pounds), while Muskrats are smaller, averaging an adult weight of only 0.9-2.27 kg (2-5 pounds). The hind feet of M. coypus can also be used to distinguish it from native Beavers and Muskrats. In M. coypus, the hind feet are partially webbed with one free digit, while Beavers have fully webbed hind feet. Muskrats have no webbing between their toes on either their front or hind legs (Evans 1970; Lowery 1974; LeBlanc 1994; California Department of Fish and Wildlife 2021). An illustrated comparison of traits, useful for M. coypus identification, is offered here https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=154118&inline through California Department of Fish and Wildlife (2021).

Size: The body length of wild adult Myocastor coypus (excluding the tail) was documented by Woods et al. (1992) to range in size from 47 to 57 centimeters (cm). The tails of M. coypus in this size range averaged a length of 37 cm (Woods et al. 1992). LeBlanc (1994) reported a slightly larger body and tail length of 61 cm and 41 cm, respectively. Male M. coypus may grow to 9.1 kg (20 pounds), while females reach a lower weight of 8.2 kg (18 pounds) (LeBlanc 1994).

Native Range: Myocastor coypus is native to South America south of the 23° latitude in the countries of Argentina, Bolivia, Brazil, Chili, Paraguay, and Uruguay (Ehrlich 1967; Banfield 1974; Kinler et al. 1987; Kinler 1992; Carter and Leonard 2002).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Myocastor coypus are semi-aquatic mammals capable of adapting to a wide variety of environmental conditions. While freshwater marshes are their preferred habitat (Holm et al. 2011), M. coypus inhabit many types of wetlands such as bayous, rivers, impoundments, farm ponds, drainage canals, and swamps, as well as brackish and saltwater marshes in coastal regions (Evans 1970; LeBlanc 1994; Bounds 2000; Holm et al. 2011). Myocastor coypus generally occupy the littoral zones of their habitat where emergent vegetation is plentiful. They are opportunistic feeders that forage on emergent, floating, and submersed plant species (LeBlanc 1994; Bounds 2000; Holm et al. 2011). Myocastor coypus use their dexterous forepaws to excavate the roots and stems of plants while grazing. Although they occasionally consume the entire plant, their primary forage are roots, rhizomes, and tubers which are especially important during winter. While they are mainly herbivorous, M. coypus incidentally consume insects as they feed on plants, and some populations occasionally eat freshwater mussels and crustaceans (LeBlanc 1994; Bounds 2000). When food is abundant, M. coypus tend to be nocturnal with peak activity occurring near midnight. Daytime feeding and general activity increases when food is limited, especially in wetlands free from frequent disturbance (Woods et al. 1992; LeBlanc 1994; Bounds 2000).

Means of Introduction: The first recorded introduction of Myocastor coypus within the United States was in 1899, in Elizabeth Lake, California, for the purpose of fur farming; however, this population failed to reproduce and establish (Evans 1970; Carter and Leonard 2002). Myocastor coypus later established populations in the wetlands of Louisiana and California through both accidental escape from captivity and intentional releases from private landowners and state agencies (Evans 1970; Lowery 1974; Woods et al. 1992; LeBlanc 1994). Dispersal of M. coypus throughout the U.S. was amplified by businesses selling them as “weed cutters” to control undesirable vegetation, through storms and hurricanes, and through transplanting by trappers and agencies seeking to establish a new species to exploit. State and federal agencies are known to have translocated M. coypus into Alabama, Arkansas, Georgia, Kentucky, Maryland, Mississippi, Oklahoma, Louisiana, and Texas, with the intent that they would control aquatic vegetation and enhance trapping opportunities (Evans 1970; Leblanc 1994; Carter and Leonard 2002).

Impact of Introduction:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Ecological	Economic	Human Health

The extensive introduction of Myocastor coypus within the United States has led to numerous ecological and economic impacts in regions where they have established at high densities (Evans 1970; Woods et al. 1992; Leblanc 1994). Myocastor coypus are opportunistic feeders that graze heavily on a variety of native emergent, floating, submersed, and woody plant species (Kuhn and Peloquin 1974; Holm et al. 2011). Their grazing has been documented to reduce the diversity and richness of plant species within the wetlands they inhabit (Shaffer et al. 1992; Evers et al. 1998). In some cases, their herbivory can cause the exclusion of native vegetation such as Broadleaf Arrowhead (Sagittaria latifolia) and Bald Cypress (Taxodium distichum) (Wentz 1971; Conner and Toliver 1987). The intense grazing of M. coypus can also hinder restoration projects through consumption of seedlings, preventing new growth and increasing overall costs (Conner and Toliver 1987; Sasser et al. 2004). Myocastor coypus reduce both the above and below ground plant biomass within their habitats (Taylor and Grace 1995; Evers et al. 1998; Ford and Grace 1998) and can negatively affect the soil building process in marshes through reducing below ground production and expansion of the root zone (Ford and Grace 1998). Additionally, the amount of carbon lost from wetland systems due to M. coypus grazing can be significant. It is estimated that the amount of carbon removed from a marsh by one M. coypus each year is approximately 15.1 kg. If it’s assumed that there are two million M. coypus in coastal Louisiana, grazing would result in a loss of carbon equivalent to that of 40,500 metric tons of coal or 12.5 million gallons of gas (Holm et al. 2011).
The economic impacts that M. coypus impose within their introduced ranges can be costly to municipalities and landowners. Nutria construct extensive burrow systems, as well as enlarge existing burrows created by native species, threatening numerous forms of public and private infrastructure (Swank and Petrides 1954; Ensminger 1956; Evans 1970; Kuhn and Peloquin 1974; Leblanc 1994; Holm et al. 2011). Burrows can weaken the structure of highway bridges, culverts, roadways, and building foundations causing considerable damage through settling and erosion (Ensminger 1956; Leblanc 1994). Levees and irrigation canals used for water control are often damaged from burrows created by M. coypus. Surface traffic or heavy rains can cause these structures destabilized by M. coypus to cave in, leaving depressions and washouts that lead to erosion, siltation, and the loss of water (Swank and Petrides 1954; Ensminger 1956; Schitoskey et al. 1972 ; Kuhn and Peloquin 1974). Myocastor coypus burrows can cut through smaller levees that serve to divide agricultural fields, resulting in the loss of water that is essential for weed control and the proper growth of crops such as rice and sugar cane. This type of damage leads to reduced crop yields, delayed or uneven growth, or the complete loss of crops (Swank and Petrides 1954; Ensminger 1956; Evans 1970; Holm et al. 2011). Myocastor coypus also threaten crop production directly through their destructive grazing habits, and can lower the yields of crops such as alfalfa, rice, wheat, barley, oats, corn, carrots, cauliflower, cucumbers, melons, and beets  (Howard 1953; Swank and Petrides 1954; Ensminger 1956; Evans 1970; Schitoskey  et al. 1972; Holm et al. 2011).
While many of the impacts imposed by M. coypus are viewed as negative, they were once considered a highly valued resource for fur and meat (Larrison 1943; Ensminger 1956; Evans 1970; Leblanc 1994; Carter and Leonard 2002; Holm et al. 2011). As the species established in high numbers within the wetlands of Louisiana during the 1940’s, M. coypus pelts became a valuable component of coastal Louisiana‘s economy, climaxing in the 1970‘s, when European processors offered luxury M. coypus products. The crash of the fur market in the 1980‘s lowered the demand and value of pelts, and in turn greatly reduced the number M. coypus harvested. This left the growth of M. coypus populations largely unchecked, and they have since emerged as a significant threat to coastal wetland sustainability (Holm et al. 2011). Myocastor coypus have also been found to be of value in marshes being managed for waterfowl production where their grazing clears stands of dense vegetation making natural ponds throughout the marsh. The newly established ponds permit the growth of plants, used as forage by waterfowl, to become established (Ensminger 1956).

References: (click for full references)

Banfield, A. W. F. 1974. The mammals of Canada. University of Toronto, Toronto, Ontario, Canada– no access

Bounds, D.L. 2000. Nutria: an invasive species of national concern. Wetland Journal 12(3):9-16.

California Department of Fish and Wildlife. 2021. California’s Invaders: Nutria Myocastor coypus. California Department of Fish and Wildlife. Sacramento, CA. https://wildlife.ca.gov/Conservation/Invasives/Species/Nutria. Accessed on 04/18/2021

Carter, J., and B.P. Leonard. 2002. A review of the literature on the worldwide distribution, spread of, and efforts to eradicate the Coypu (Myocaster coypus). Wildlife Society Bulletin 30(1):162-175.

Conner, W.H., and J.R. Toliver. 1987. The Problem of Planting Louisiana Swamplands with Nutria (Myocastor coypus) are Present. Pages 42-49 in Third Eastern Wildlife Damage Control Conference, 1987. University of Nebraska. Lincoln, NE.

Ehrlich, S. 1967. Field studies in the adaptation of Nutria to seasonal variations. Mammalia 31:347-360. – no access

Ensminger, A.B. 1956. The economic status of Nutria in Louisiana. Pages 185-188 in Proceedings of the Southeastern Association of Game and Fish Commissioners.

Evans, J. 1970. About Nutria and Their Control. Bureau of Sport Fisheries and Wildlife, Denver Wildlife Research Center.

Evers, D.E., Fuller D.A., and J.M. Visser. 1998. The Impact of Vertebrate Herbivores on Wetland Vegetation in Atchafalaya Bay, Louisiana. Estuaries 21(1):1-13.

Ford, M.A., and J.B. Grace. 1998. Effects of vertebrate herbivores on soil processes, plant biomass, litter accumulation and soil elevation changes in a coastal marsh. Journal of ecology 86(6):974-982. https://doi.org/10.1046/j.1365-2745.1998.00314.x

Holm, G.O., E. Evers, and C.E. Sasser. 2011. The Nutria in Louisiana: a current and historical perspective. Department of Oceanography and Coastal Science, School of the Coast and Environment Louisiana State University, Baton Rouge, LA. https://saveourlake.org/wp-content/uploads/PDF-Documents/our-coast/LPBF-LSU-Nutria-FINAL-11-22-11.pdf

Howard, W.E. 1953. Nutria (Myocastor coypus) in California. Journal of Mammalogy 34(4):512-513.

Kinler, N. W. 1992. Biology and ecology of Nutria. Page 75 in Proceedings of the thirteenth annual meeting of the American Society of Wetland Scientists 31 May- 6 June 1992, New Orleans, Louisiana, USA– no access

Kinler, N. W., G. Linscombe, and P R. Ramsey. 1987. Nutria. Pages 326-343 in M. Novak,J. A. Baker, M.E. Obbard, and B. Malloch, editors. Wild furbearer management and conservation in North America. The Ontario Trappers Association, Ontario – no access

Kuhn, L.W., and E.P. Peloquin. 1974. Oregon's Nutria Problem. Proceedings of the 6th Vertebrate Pest Conference:101-105. http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1026&context=vpc6

Larrison, E.J. 1943. Feral Coypus in the Pacific Northwest. The Murrelet 24(1):3-9.

LeBlanc, D.J. 1994. Nutria in S. E. Hygnstrom, R. M. Timm and G. E. Larson, eds. Prevention and control of Wildlife Damage. Pages B71-80 in Cooperative Extension Service, University of Nebraska, Lincoln.

Lowery, G.H., Jr. 1974. The Mammals of Louisiana and its Adjacent Waters. Louisiana State University Press.

Sasser, C.E., G.O. Holm, Jr., J.M. Visser, and E.M. Swenson. 2004. Thin-mat marsh enhancement demonstration project TE-36. School of the Coast and Environment, Louisiana State University, Baton Rouge, LA. https://www.researchgate.net/profile/Jenneke_Visser/publication/242118364_THIN-MAT_FLOATING_MARSH_ENHANCEMENT_DEMONSTRATION_PROJECT_TE36/links/00b7d51d1d793a1772000000/THIN-MAT-FLOATING-MARSH-ENHANCEMENT-DEMONSTRATION-PROJECT-TE36.pdf

Schitoskey, F. Jr., J. Evans, and G.K. LaVoie. 1972. Status and Control of Nutria in California. Proceedings of the 5th Vertebrate Pest Conference:15-17.

Shaffer, G.P., C.E. Sasser, J.G. Gosselink, and M. Rejmanek. 1992. Vegetation dynamics in the emerging Atchafalaya Delta, Louisiana, USA. Journal of Ecology 80(4):677-687. https://www.jstor.org/stable/2260859

Swank, W.G., and G.A. Petrides. 1954. Establishment and food habits of the Nutria in Texas. Ecology 35(2):172-176.

Taylor, K.L., and J.B. Grace. 1995. The effects of vertebrate herbivory on plant community structure in the coastal marshes of the Pearl River, Louisiana, USA. Wetlands 15(5):68-73. https://doi.org/10.1007/BF03160681

Wentz, W.A. 1971. The impact of nutria (Myocastor coypus) on marsh vegetation in the Willamette Valley, Oregon. Unpublished M.S. thesis. Oregon State University, Corvallis, OR.

Woods, C.A., L. Contreras, G. Willner-Chapman, and H.P. Whidden. 1992. Myocastor coypus. Mammalian Species 398:1-8.

Other Resources:
US Fish and Wildlife Service Ecological Risk Screening Summary for Myocastor coypus

Author: Procopio, J.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.