Nutria

Wildlife Services

October 2005

The nutria (Myocastor coypus), a large, semi-aquatic rodent native to South America, was originally brought to the United States in 1889 for its fur. When the nutria fur market collapsed in the 1940s, thousands of nutria were released into the wild by ranchers who could no longer afford to feed and house them. Entrepreneurs began selling the herbivores to control noxious weeds. Wildlife agencies further expanded the range of the nutria by introducing the species into new areas of the United States. While the nutria did devour weeds and overabundant vegetation, they also destroyed aquatic vegetation, crops, and wetland areas.

Recognized in the United States as an invasive wildlife species, nutria has been found in 22 states, and is currently established in 16 states. The nutria's relatively high reproductive rate combined with a lack of population controls have resulted in a proliferation of the species. In many regions the damage they cause is severe. Nutria are most abundant in the Gulf Coast States, but they are also a problem in other southeastern States and along the Atlantic coast. In addition to damaging vegetation and crops, nutria are known for destroying the banks of ditches, lakes, and other water bodies. Of greatest significance, however, is the permanent damage nutria can cause to marshes and other wetlands. In these areas, nutria feed on native plants that hold wetland soil together. The destruction of this vegetation exacerbates the loss of coastal marshes that has been set in motion by rising sea levels.

Identification

From a distance, nutria are sometimes mistaken for beavers. Both are semi-aquatic and dark colored, and their large incisors are yellow to orange in color. Upon closer inspection, however, the two species are easy to distinguish. Adult nutria generally weigh less than 20 pounds, while adult beavers may exceed 75 pounds. In addition, beavers generally have darker fur than nutria. The most obvious difference between the two animals is the look of their tails. While beavers have tails that are flat and broad, nutria have thin, round tails that are pointed at the tip.

Nutria are approximately 2-feet long, and have a robust, highly-arched body. Their legs are short and their color may range from yellowish to dark brown. Because nutria spend much of their time in the water, they are highly adapted for a semi-aquatic existence. Their hind feet are webbed for swimming, and their eyes, ears, and nostrils are set high on their heads, so they can stay above the waterline when swimming. In addition, valves in their nostrils and mouths can seal out water. Nutria are excellent swimmers and, when pursued, they can swim long distances underwater and see well enough to evade capture.

Nutria adapt to a wide variety of habitats, even those that may be considered unsuitable. In the United States, the largest nutria populations are located in coastal areas along Gulf Coast States, preferably in freshwater marshes. These regions have an abundance of emergent aquatic vegetation, small trees, and shrubs. Within these areas, nutria are found in farm ponds and other fresh water impoundments, drainage canals, rivers, bayous, freshwater and brackish marshes, and swamps. In cities, they can be found under buildings, in overgrown lots, on golf courses, and in storm drains.

Nutria can live in burrows and in dense vegetation or under other protective covering. In shallow water, nutria often use elevated, flattened circular platforms of dead vegetation for feeding, loafing, grooming, birthing, and escape from predators. These platforms of vegetation are frequently misidentified as muskrat houses.

Damage

Nutria damage is evident to varying degrees in every area they are found. The most noticeable damage is the result of burrowing. Nutria are notorious in Louisiana and Texas for undermining and breeching water-retention levees in flooded fields used to produce rice and crawfish. Nutria burrows can also damage flood control levees that protect low-lying areas; weaken the foundations of reservoir dams, buildings, and roadbeds; and erode the banks of streams, lakes, and ditches.

Nutria damage, however, is not limited to burrowing. Depredation on crops is well documented.
In the United States, sugarcane and rice are the primary crops damaged by the nutria. Grazing on rice plants can significantly reduce yields, and damage can be severe in localized areas. Other crops damaged by the nutria, include corn, milo, sugar and table beets, alfalfa, wheat, barley, oats, peanuts, various melons, and a variety of vegetables. This depredation can lead to significant losses, especially for small farmers.

Of critical importance, is the negative impact this invasive species has on native vegetation and associated wetlands. In Louisiana, some nutria feed on seedling baldcypress with such intensity that the trees cannot survive. Similarly, nutria can severely damage coastal marshes by decimating native plants that hold marsh soils together and support the survival of native wildlife species. The impact of nutria on disappearing marshlands along the Gulf Coast has been well documented for several years, and more recently in the Delmarva marshes along the Chesapeake Bay in Maryland. In some cases, nutria damage to marsh vegetation and soils is so severe that these resources are permanently lost. The destruction of these marshlands also increases the vulnerability of adjacent upland sites to erosion and flooding during storms.

Nutria can also impact public health and safety. The rodents can serve as hosts for several pathogens, including tuberculosis and septicemia, which are transmissible to people, pets, and livestock. In addition, nutria can carry parasites, such as nematodes, blood flukes, tapeworms, and liver flukes. Many of these organisms are found in nutria feces and urine and can contaminate drinking water supplies and swimming areas.

How Wildlife Services Manages the Damage

Wildlife Services (WS), a program within the U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service, is authorized by Congress to resolve damage caused by wildlife. A 1997 Executive Order further directs USDA, in cooperation with other Federal agencies, to provide national leadership and oversight in managing invasive species, such as the nutria. When WS is asked to provide nutria assistance, program specialists work closely with Federal, State, and local governments to develop comprehensive management plans that include provisions for protecting native vegetation, marsh soil, and other natural resources against nutria damage.

Preventative measures should be used whenever possible, especially in areas where nutria damage is prevalent. Habitat management, which involves manipulating vegetation and water sources attractive to nutria, can be effective in reducing rodent numbers. Small areas, such as gardens, can be enclosed by partially buried fences. Wire tubes can also be used to protect baldcypress and other tree seedlings from nutria damage, and bulkheads can be used to deter burrowing into banks. These methods, however, are not always effective or practical, and can be expensive to implement.

When damage cannot be resolved by nonlethal measures, WS has the expertise to remove nutria populations in problem areas. Relocation is not a viable option because nutria are an invasive species that threaten both native wildlife species and vegetation. Relocating nutria to a new area just relocates the problem, and can lead to the establishment of new nutria colonies and new damage concerns.

Additional Information

For more information about this and other WS programs, contact WS Operational Support Staff at (301) 734-7921 or write to:
USDA, APHIS, WS
4700 River Road, Unit 87
Riverdale, MD 20737

For additional information about WS, visit the program's Web site at http://www.aphis.usda.gov/ws.

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