The nutria, Myocastor coypus, is a large semi-aquatic rodent. The generic name is derived from two Greek words (mys, for mouse, and kastor, for beaver) that translate as mouse beaver. The specific name coypus is the Latinized form of coypu, a name in the language of the Araucanian Indians of south-central Chile and adjacent parts of Argentina for an aquatic mammal that was possibly this species. In most of the world the animal is called coypu, but in North America the animal is called nutria. In the rest of the world, nutria is the name of the fur of the animal.
Nutria are smaller than a beaver but larger than a muskrat; unlike beavers or muskrats, however, it has a round, slightly haired tail. The forelegs are small compared with its body size. The forepaws, have five toes; four are clawed and the fifth is reduced in size. The digits are used to groom and to excavate roots, rhizomes, and burrows, and are used in feeding. The hindfoot consists of four webbed, strongly clawed toes and one unwebbed toe. The hind legs are large compared with the forelegs; consequently, when moving on land, the nutria’s chest drags on the ground and its back appears hunched. Although appearing awkward, the nutria is capable of fast overland travel for considerable distances. The ears are small and the eyes are set high on the head. The nose and mouth are valvular (i.e., can be closed to prevent entry of water), and nutria are capable of swimming long distances underwater. When pursed while underwater, nutria can see and will take evasive action to avoid capture.
Males are slightly larger than females. Nutria weigh an average of 12.0 pounds (5.4 kg). Females have four pairs of mammary glands that are located on the side of the body, rather than on the belly. Presumably, this positioning of the mammary glands allow the young to nurse with their nose above the water’s surface while the mother is floating.
The nutria’s yellow or brown outer hair looks shaggy and unappealing, but it covers a lush fur undercoat, also called nutria, that is popular for use in clothing. Nutria are farmed and trapped for this fur.
Nutria breed year round and are extremely prolific. Males reach sexual maturity between 4 and 9 months, whereas, females reach sexual maturity between 3 and 9 months. Sexual maturity may vary with habitat quality. With a gestation period of only 130 days, in one year, an adult nutria can produce two litters and be pregnant for a third. The number of young in a litter ranges from 1-13 with an average of 4.5 young. Females can breed within a day of having a litter. Litter size can vary with age of female, habitat quality and time of year. The young nutria at birth are fully furred and the eyes are open. Newborn nutria feed on vegetation within hours and will nurse for 7-8 weeks.
Habitat and dieting habits
Nutria are well adapted for movement on land, however, are more at home in the water. In the coastal marshes they are often seen moving about leisurely in the daytime, but their period of greatest feeding activity is just prior to sunrise and after sunset. Nutria are strict vegetarians, consuming their food both on land and water, where they shove aquatic plants to their mouths with their forepaws. These animals consume approximately 25 percent of their weight daily. Nutria predominately feed on the base of plant stems and dig for roots and rhizomes in the winter. They often construct circular platforms of compacted, coarse emergent vegetation, which they use for feeding, birthing, resting and grooming. Nutria may also construct burrows in levees, dikes and embankments.
Nutria coypu as pests
Nutria damage is evident to varying degrees in every area they are found. Burrowing causes the most noticeable damage. 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 also can 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, with severe localized loss. 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. The negative impact this invasive species has on native vegetation and associated wetlands is critically important. In Louisiana, some nutria feed on seedling bald cypress 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 and the Chesapeake Bay in Maryland has been well documented. Nutria have caused widespread ecosystem changes. 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 also can impact public health and safety. The rodents can serve as hosts for several pathogens, including tuberculosis and septicemia, which can infect people, pets, and livestock. In addition, nutria can carry parasites, such as blood flukes, tapeworms, and liver flukes and a nematode known to cause a rash called “nutria itch.” Many of these organisms—found in nutria feces and urine—can contaminate drinking water supplies and swimming area.
Impacts by nutria to agriculture include foraging on crops, weakening irrigation structures by digging burrows, and potential disease transmission to livestock. Crop damage is most prevalent in areas adjacent to aquatic habitats supporting nutria, and especially where nutria are abundant. Crops primarily damaged by nutria are sugarcane and rice, but also include corn, milo (grain sorghum), sugar and table beets, alfalfa, wheat, barley, oats, peanuts, and various melons and vegetables. In Louisiana, nutria commonly undermine and break through water-retaining levees in flooded fields used for rice and crawfish production. Nutria burrows can weaken flood control levees that protect low-lying areas as well as roadbeds, stream banks, dams, and dikes under heavy weight. Nutria can be infected with pathogens (e.g., leptospirosis) and parasites transmissible to livestock, which is especially a concern in situations where livestock drink from water contaminated by nutria urine and feces.
Transmission of diseases and parasites carried by nutria to humans is not well-documented, but could potentially involve toxoplasma, chlamydia, and salmonella. Diseases are common in captive populations where too many nutria are housed in close proximity and where cleaning standards are low. In turn, these conditions pose the greatest risk to human handlers who do not wear appropriate personal protective equipment such as gloves while handling animals, or masks while cleaning pens. Nutria parasites most often transmitted to humans are nematodes and blood flukes (Strongyloides myopotami and Schistosoma mansoni) that cause what is commonly known as “swimmer’s itch”.