Nutria

Identification | Biology | Damage ID | Management | Resources

Figure 1. Nutria (Myocastor coypus). Photo by Christine Eustis of USDI-Fish and Wildlife Service (USFWS). 

Learning Objectives 

  1. Explain how the biology of nutria determines the techniques for control. 
  2. Determine the signs of an infestation of nutria. 
  3. Explain the techniques for managing nutria. 

Identification 

Nutria (Myocastor coypus, Figure 1) are large, dark-colored, semi-aquatic rodents native to South America. They are members of the family Myocastoridae. Nutria may be misidentified as beavers or muskrats, especially when swimming, but the resemblances are superficial. Other names used for nutria include coypu, nutria-rat, South American beaver, Argentine beaver, and swamp beaver. 

Legal Status 

Nutria are protected as furbearers in some localities due to the economic importance of their fur. Permits may be necessary to control individuals that are damaging property. In other areas, nutria are considered an invasive species, have no legal protection, and can be taken at any time by any legal means. Always be familiar with local laws and regulations governing wildlife and obtain the necessary permits and expertise to do the job correctly.  

Physical Description 

Nutria have short legs and a robust, highly arched body approximately 24 inches long. The round tail is 13 to 16 inches long and scantily haired. Males are slightly larger than females, but the average weight for both sexes is 12 pounds. Males and females may grow to 20 pounds and 18 pounds, respectively.  

Nutria have several adaptations for living a semi-aquatic life. The eyes, ears, and nostrils are set high on the head. The nostrils and mouth have valves that seal out water. The mammae, or teats, of the female are high on the sides, which allows young to suckle while in water. Nutria can swim long distances underwater and see well enough to evade capture. The dense, gray underfur of nutria is overlaid by long, glossy guard hairs that vary in color from dark brown to yellow-brown. The forepaws have 4 well-developed, clawed toes and 1 vestigial toe. Four of the 5 clawed toes on the hind foot are interconnected by webbing; the fifth outer toe is not. The hind legs are much larger than the forelegs. When moving on land, nutria may drag their chests and appear to hunch their backs. Nutria have large incisors that are yellow-orange to orange-red on the outer surface. 

Species Range 

The original range of nutria was south of the equator in temperate South America.  

Figure 2. Distribution of the nutria in North America. Image by Prevention and Control of Wildlife Damage . 

They have been introduced into other areas, primarily for their fur, and populations now are found in North America, Europe, the former Soviet Union, the Middle East, Africa, and Japan. Nutria were sold to the public to control weeds in the southeast US. A hurricane in the late 1940s aided in dispersal by scattering nutria over wide areas of southwest Louisiana and southeast Texas, where populations now are the densest in the US (Figure 2). 

Nutria have been reported in at least 40 states and 3 Canadian provinces, and at least ⅓ of those states currently have viable populations, some of which are important economically to the fur industry. Adverse climatic conditions, particularly extreme cold limit the expansion of the range of nutria in North America. 

Voice and Sounds 

Nutria emit a low octave, nasal “moo” and a nasal-sounding “nan-cy.” 

Tracks and Signs 

On-site observations of nutria and their burrows are the best indicators of presence. Tracks often can be found near crawl-outs, slides, trails, and exposed entrances to burrows (Figure 3). A drag-mark left by the tail may be evident between the footprints.  

Figure 3. Tracks of nutria. Image by Dee Ebbeka.

Droppings may be found floating in the water, along trails, or where nutria feed. Droppings are dark green or black in color, cylindrical, 2 inches long, and ½ inch in diameter. Each dropping usually has deep, parallel grooves along its entire length (Figure 4).  

Figure 4. Droppings of nutria. Photo by John Consolini.