Nutria (Myocastor coypus) are large nocturnal rodents native to southern South America. They were first introduced into several states in the early 1900s for fur farming, but they have since been widely spread intentionally and unintentionally, and currently there are believed to be populations in over a dozen states. They tend to do better in milder climates.
Nutria can generally reach weights of 25 pounds or more, and will eat almost any green plant and roots. Voracious eaters, they can consume up to 25% of their weight per day. Although they will eat large quantities of undesirable aquatic and shoreline vegetation, they also eat large amounts of desirable aquatic vegetation, and a large nutria population will rapidly reduce productive wetland and marsh areas to denuded tunnels of open water having little wildlife habitat value. They also eat farm crops, compete with muskrats and waterfowl, and are also vectors for a variety of parasites and wildlife diseases. They are burrowers, creating extensive tunnels in pond and canal banks. They may also enlarge muskrat burrows around levees, or cut directly into the levees themselves, eventually causing them to break and flood adjacent croplands. Nutria occasionally damage highway bridges and culverts by burrowing around them. In the south, millions of dollars are being spent on nutria control.
Nutria reproduce rapidly; they breed year-round, reach sexual maturity quickly, and produce several litters per year, of up to 11 offspring per litter (although 4-6 is more normal). Nutria were eradicated in California by 1978, and are now assumed to be extinct in Idaho and Montana, but thanks to the mild climate of the Pacific Northwest, they are rapidly becoming a problem, particularly in Washington and Oregon. A nutria workgroup has now been established to develop a regional nutria control plan.
The links provided may be outside the EPA.gov domain.
Marsh Loss & Exclosure Study
National management plan (expected on website late 2008)