By: Texas A&M AgriLife Extension Service—Wildlife Services
Nutria (Myocastor coypus) are large, semiaquatic rodents native to South America. They resemble beavers or muskrats but differ by having long, round tails and webs between the inner four toes of their hind feet, with the outer toes free. Their closest relative in North America is the porcupine.
Nutria were first imported from South America to the United States in 1899. During the 1930s, many fur farms were established on the West and Gulf coasts. The greatest dispersal of nutria occurred in the late 1940s when get-richquick promoters, selling nutria as “aquatic weed cutters,” transplanted them throughout the Southeast. Nutria are now found in at least 40 states and Canadian provinces. They are found in all areas of Texas except extreme west Texas and the Panhandle (see Fig. 1).
Nutria are almost exclusively vegetarian and normally consume about 3 pounds of food a day. Generally, nutria feed on the soft, succulent parts near the bases of plants, but they will occasionally eat the entire plant. When available, coarse plants such as cattail, cord grass and reeds are their favorites, but they will also eat soft grasses such as Bermudagrass or soft water plants such as duckweed. In agricultural areas they sometimes feed on various cultivated crops.
Biology and Reproduction
- Adult weight: Average 8 pounds.
- Total length: Body approximately 24 inches; tail approximately 16 inches.
- Color: Brownish to blackish.
- Gestation period: About 130 days.
- Litter size: One to nine young with an average of five, usually born in a burrow dug in a pond dam, river bank or similar area.
- Number of litters: Approximately three litters per year, depending on weather conditions.
- Sexual maturity: 4 months under optimum conditions.
- Life span: About 2 years in the wild and 15 to 20 in captivity.
- Social structure: The social structure varies according to the environment. In small ponds, marshes or other small bodies of water, nutria tend to have close-knit communities consisting of four to 20 individuals which are usually related. In agricultural areas where the location of food supplies changes frequently, nutria usually do not form colonies and there is a constant interchange of individuals between areas.
Damage
Nutria damage occurs when they eat desirable vegetation, girdle trees, or burrow into banks, dams or dikes. Although some damage occurs in corn, grain sorghum, rice, vegetables, ornamentals, tree plantings, road beds and manmade structures, the greatest amount of damage is caused by nutria digging their burrows into pond dams, levees or watershed structures. Left unchecked, these burrows may weaken the dam and cause it to wash out or collapse. When nutria become a nuisance or cause damage, they may need to be controlled.
Damage Prevention and Control
Nutria control is best accomplished as soon as there is evidence of damage. Once nutria populations become established over a large area, control can be difficult.
Habitat Manipulation
Good farming practices such as vegetation control, proper drainage and land grading will often discourage nutria from becoming established. Removing unwanted trees, weeds and brush close to and around the water’s edge is often an effective control method, as it eliminates much of the food and cover used by nutria. In addition, precision grading of pond dams and drainage ditches to eliminate steep slopes will discourage nutria by eliminating potential den sites.
Trapping
A variety of traps and trapping methods is effective in controlling nutria. Cage traps, leghold traps, conibear traps and snares can be used. The effectiveness of any trap is determined by the trapper’s knowledge of nutria habits, as well as proper trap selection and placement.
Cage Traps. Cage traps can be used where a nutria population is small. Cage traps of the size used for raccoons or opossums are best suited for nutria. The traps should be placed in areas where the damage is occurring. Sweet potatoes or carrots are the best baits to use with cage traps. Trapping success sometimes can be increased by pre-baiting for several days before the traps are set.
Leghold Traps. Double long-springed or coilspringed traps should be at least number two size in jaw spread and strength. Baited sets can be made using carrots or sweet potatoes. The most effective set, however, is the trail set. Nutria establish trails when traveling to and from feeding areas or bodies of water. The trap should be placed just off the center of the trail to ensure that a foot is caught, and then covered lightly with leaves or mud. The trap can also be set just beneath the water surface where the trail enters the water. Such leghold trap sets should be made as drowning sets, which allows the trapped nutria to swim to deeper water. Then a locking device prevents the animal from surfacing for air (see Fig. 2).
Conibear Traps. The conibear trap, size 220 or 330, is the most common trap used for controlling nutria (see Fig. 3). There is a variety of sets that can be made with conibear traps, such as den, trail and culvert sets. The Texas Parks and Wildlife Department regulations require that conibear traps with diagonal openings larger than 10 inches be set in a minimum of 6 inches of water. Inexperienced trappers should be extremely cautious with conibear traps and follow trap setting instructions. It is wise to have an experienced trapper demonstrate the proper setting techniques.
Snares
Snares can sometimes be used when other trapping methods are not possible. A snare consists of a flexible wire cable, preferably 40 inches long and 3/32 inch thick, made into a loop which will tighten on the animal’s body as it passes through. A simple locking device on the snare holds the loop tight. Ready-made snares also can be purchased through trapping supply companies or from farm and ranch supply stores. Snares are most effective when set along feeding and travel trails. Slides on pond dams or banks are also ideal sites. The loop of the snare should be approximately 6 to 8 inches in diameter when set. The bottom edge of the snare should be at, or just below, the ground surface. Since snares do not usually kill nutria, they must be securely staked. Snares are inexpensive, easy to carry and simple to set. However, they are not as escape-proof as other types of traps, they are sometimes knocked down by nutria or other animals, and they must be checked frequently.
Shooting
Where it is legal, nutria can be shot at night using a shotgun with #4 buckshot, BB’s, or #2 birdshot. A spotlight equipped with a red filter lens probably will be required. The use of rifles is not recommended because of the possibility of bullets ricocheting off the water. When spotlighting, it is best to set up the shoot location about an hour before dark. Sit in an area that provides a good view for shooting. Spotlights with power packs and filters are available from many sporting goods stores.
Chemical Control
Zinc phosphide is the only chemical registered for the control of nutria. It is a RestrictedUse Pesticide and can be used only by a licensed pest control operator or a person who has a private applicator’s license permitting the use of Restricted-Use chemicals.
Zinc phosphide is a black powder which looks like gunpowder. It is applied to carrot or sweet potato baits, and will kill nutria within several hours after the treated bait is eaten. For best results, the bait should be placed on floating rafts (see Fig. 4) near den or burrow entrances or near natural feeding areas. The number of bait stations required is determined by the nutria population. An area with a small population of nutria will require only one or two bait stations. Areas with higher populations will require more. The rafts should be pre-baited daily with fresh, untreated carrots or sweet potatoes, and all uneaten bait from the previous night should be removed. After the nutria have fed on the untreated bait for several nights in a row, the zinc phosphide can then be applied to the bait. When using zinc phosphide, the label directions should always be read, understood and followed precisely
Chemical control is most effective during winter months when most vegetation is dormant. Keep in mind that when nutria populations are small, trapping or shooting can be just as effective as chemical control.
Restrictions
Nutria are classified as furbearers in Texas, but it is legal to trap them. Under state law, a person may trap a furbearing animal at any time if it is causing damage; however, the pelt can be sold only during the furbearer season and with the proper licenses. Other furbearers include otter, mink, ringtailed cat, badger, skunk, weasel, raccoon, opossum, beaver, muskrat, fox and civet cat.
Landowners wishing to live trap nutria and relocate them after they have been caught should notify representatives of the Texas Parks and Wildlife Department.
For additional information contact the nearest office of Texas AgriLife Extension—Wildlife Services.
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