Nutria*
Order Rodentia : Family Myocastoridae : Myocastor coypus (Molina)

Description. A large rodent, nearly as large as a beaver but with long, rounded, scaly, ratlike tail; hind feet webbed; incisors orange-colored; female with mammae along each side of back, not on belly; upperparts reddish brown; the underfur dark slaty; tip of muzzle and chin white. External measurements of adults average: total length, 800-900 mm; tail, 350-400 mm; hind foot, 130-140 mm. Total length may reach 1.4 m. Weight, normally 8-10 kg.

Distribution in Texas. Known from aquatic habitats in eastern two-thirds of state.

Habits. Throughout much of their natural range in South America, nutria prefer a semiaquatic existence in swamps, marshes, and along the shores of rivers and lakes. In southern Chile and Tierra del Fuego they are found mainly in the channels and bays separating the various islands off the coast. Here, their habitat seems to be mostly in the estuaries of glacier-fed streams, and colonies of nutria are often seen swimming among the floating ice blocks in the vicinity of glaciers. Apparently, the nutria is equally at home in salt and fresh water.

They are docile creatures, much like the beaver in this respect, and can be handled easily in captivity. They are almost entirely nocturnal, consequently their presence in an area usually is revealed only by their trails, feces, and lengths of cut vegetation that have been left in their trails. They are not extensive burrowers. Burrows that have been examined were approximately 20 cm in diameter and extended into the bank for a distance of over 1 m. Often they were open at both ends, with the entrance toward the river usually above water level. Some of the burrows are under roots of trees that are exposed along the banks of the river or stream. Their nests are made of reeds and sedges built up in large piles somewhat after the fashion of a swan’s nest. These are built on land among the marsh vegetation and close to the water’s edge.

Their natural food consists almost entirely of aquatic and semiaquatic vegetation, but when these animals live along the coast they also feed upon shellfish. Cattails, reeds, and sedges appear to be especially prized items of food. When established near gardens, they take cabbage readily; they are also fond of carrots and sweet potatoes.

These animals appear to breed throughout the year. Each adult female produces two or three litters a year. The gestation period is from 127 to 132 days. The number of young per litter ranges from two to 11 and averages about five. At birth the young are fully furred, and their eyes are open; they are able to move about and feed upon green vegetation within a few hours. At that time they weigh approximately 200 g. They mature rapidly, increasing at the rate of about 400 g per month during the first year, and reach sexual maturity at the age of 4 or 5 months. Females sometimes give birth to their first litter when they themselves are 8 or 9 months old. The maximum length of life for nutria kept in captivity is 12 years, but the life span in the wild probably is considerably less.

These animals are important fur producers in their native range. They are reared extensively on fur farms in South America and most of their pelts are sold on the European market. On the American market, nutria pelts have at times been of some value, but currently there is no market for nutria pelts. Because of their known competition with muskrats, which are well-established and valuable fur-producing animals in this country, it appears that muskrats may be driven out and replaced by the much less desirable nutria.

They have been widely introduced in Texas as a "cure-all" for ponds choked with vegetation. They do reduce many kinds of aquatic plants, but they will not eat "moss" (algae) and many of the submerged plants. At times they do the job too well. The trouble is that once nutrias get established in a lake, their high reproductive capacity soon results in overpopulation. There are so many nutrias that the available food supply will not satisfy them, and then trouble begins. The animals move into places where they are not wanted or where they destroy vegetation that is valuable for such wildlife as waterfowl and muskrats. A case in point is Eagle Lake in Colorado County. There, a stocking of nutrias increased to the point where the animals seriously damaged the waterfowl values of the lake. Hundreds of dollars were spent in attempts to eradicate the pests.

Currently, nutria populations in Texas are moderately high and on the increase. Unless the market for nutria improves, a serious and costly overpopulation problem is likely in the very near future.

* nonnative species

Photo courtesy of Texas Parks and Wildlife.