Nutria

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

Factsheet

Wildlife Services October 2005

APHIS
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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