Damage by nutria occurs throughout their range. The ranges of nutria, beavers, and muskrats overlap in many areas and damage caused by each may be similar. Therefore, careful examination of sign left at the site is necessary to identify the species that is responsible. Most damage is from feeding or burrowing. In the US, most damage occurs along the Gulf Coast of Louisiana and Texas and around Chesapeake Bay.
Damage to Structures
Most damage caused by nutria is due to their burrowing activity. Nutria are notorious for undermining and breaking through water-retaining levees in flooded fields used to produce rice and crawfish. Burrows of nutria may weaken flood-control levees in low-lying areas. In some cases, tunneling in levees is so extensive that water will flow unobstructed, necessitating complete reconstruction of the structure.
Nutria sometimes burrow into Styrofoam® floats under boat docks and wharves, causing the structures to lean and sink. They burrow under buildings, which may lead to uneven settling or failure of foundations. Burrows can weaken roadbeds, banks, levees (Figure 5), dams, and dikes, which may collapse when soil is saturated by rain or high water, or when subjected to the weight of vehicles, farm machinery, or livestock on the surface. The action of rain and waves can wash out and enlarge collapsed burrows and compound the damage.
Damage to Livestock and Pets
Nutria present an indirect threat to pets and livestock. The feeding and digging of nutria impact sources of food for other species and the integrity of levees and embankments.
Damage to Landscapes
Damage caused by nutria, muskrats, and Norway rats often is confused in fields of rice. Nutria and muskrats damage rice plants by clipping stems at the water line in flooded fields. Norway rats clip stems above the surface of the water.
In the US, sugarcane and rice are the primary crops damaged by nutria. Grazing by nutria on rice plants may reduce yields significantly and damage can be locally severe. Stalks of sugarcane often are gnawed or cut during the growing season, with only the basal internodes of the cut plants that are eaten. Other crops that may be damaged include corn, grain sorghum, beets, alfalfa, wheat, barley, oats, peanuts, melons, and a variety of vegetables from home gardens and farms.
Trees girdled by nutria often have no marks from their teeth, as bark may be peeled from the trunk. The crowns of seedling trees usually are clipped, similar to damage by rabbits and discarded along with other woody portions of the plant. Nutria girdle fruit, nut, and shade trees and ornamental shrubs. They dig in lawns and golf courses when feeding on sod grasses. Damage from gnawing on wooden structures is common. Nutria gnaw on Styrofoam® floats used in commercial crawfish ponds.
At high densities and under certain adverse environmental conditions, foraging of nutria can substantially impact plant communities. In Louisiana, nutria often feed on seedling baldcypress and can cause the complete failure of stands. Excessive use of emergent marsh plants can damage vegetation that is desirable and aggravate coastal erosion problems by destroying vegetation that holds marsh soils together. Nutria are fond of tubers of grassy arrowhead and may destroy stands that have been propagated as food for waterfowl.
Health and Safety Concerns
Nutria can be infected with several pathogens and parasites that can be transmitted to humans, livestock, and pets. The role of nutria in the spread of diseases such as equine protozoal myeloencephalitis, leptospirosis, hemorrhagic septicemia, paratyphoid, and salmonellosis is not well documented. They may host several parasites, including the nematodes and blood flukes that cause “nutria itch” or “swimmer’s itch,” the protozoan responsible for giardiasis, tapeworms, and common liver flukes. The threat of disease may be an important consideration when livestock drink water that is contaminated by feces and urine of nutria. Nutria play a role in spreading tuberculosis, false tuberculosis, and septicemia. People should exercise caution when handling nutria to avoid being scratched and bitten. Feeding should be avoided also as bites have occurred where nutria were being fed by the public.