Nutria: What You Should Know About the Invasive Rodent

Nutria Myocastor coypus
delectus / Getty Images

Nutria are large, semi-aquatic rodents native to South America with coarse brown fur, webbed feet, and a pair of long front teeth with orange tips. Larger than muskrats and smaller than beavers, two native mammals that share similar habitats, nutria first found their way to the United States around the turn of the 20th century as part of a then-booming fur trade. Its fur is similar to that of beavers, having a coarse, waterproof, outer layer and a shorter, soft layer for warmth beneath. As populations of native fur-bearing animals decreased in some areas, nutria provided a new source of revenue for trappers in rural parts of Louisiana, Texas, Maryland, and California.

After numerous escapes, nutria established rapidly growing populations, with one adult nutria capable of birthing up to 26 young each year (which reach sexual maturity between 4 and 9 months of age). The animals are also prolific eaters, capable of consuming up to 25% of their weight each day in vegetation. Because nutria feed primarily on the base of plant stems, they can quickly consume and kill large swaths of vegetation, which is particularly concerning in areas with rising coastlines, where marsh grass provides a pivotal line of defense against land loss. As a result, some states, including Louisiana and Maryland, have instituted bounty programs, marsh plantings, and education efforts to attempt and combat the nutria's damage.

Portrait of coypu by the river. Close-up of large orange teeth are clearly visible on this coypu
Close-up of large orange teeth on a nutria. Vronja_Photon / Getty Images

How Nutria Became an Invasive Species

The first nutria introduction happened in California in 1899, and by the 1930s the animal was in seven states. Like many non-native species imported because of economic value, it eventually escaped, leading to millions spent in federal and state funds on eradication efforts. In Louisiana, Tabasco founder E. A. McIlhenny lost at least 150 animals from his coastal lands following a 1940 hurricane. He thought the rodents would be eaten by alligators, but they survived, rapidly expanding in population across the region, and likely breeding with other nutria that trappers intentionally released to create a local population.

By the 1950s, nutria were damaging rice and sugarcane fields across south Louisiana, and the state began paying trappers 0.25 cents per nutria pelt in an attempt to minimize their impact. This bounty stopped in the 1960s, when nutria fur exports to Europe boomed. But by the end of the 1980s, fur was losing its status as a prized commodity, and nutria populations were again ballooning across marshes in Louisiana, as well as in Maryland. Both states instituted control programs to try and stop the nutria's damage. The animal has since been eradicated from many of Maryland's vulnerable marsh areas, while millions remain in Louisiana despite more than 2.5 million being harvested since the state's bounty program began in 2002.

Problems Caused by Nutria

Nutria are opportunistic feeders, with a broad diet comprised of more than 60 plant species found in Louisiana alone. Attracted to wetlands that contain a reliable source of nutrient-rich fresh water, the rodents can consume large amounts of marsh biomass and in certain cases can cause the collapse of marsh locally. Scientific studies investigating effects of nutria on marsh habitats consistently conclude that nutria grazing is damaging to marsh and young forest vegetation. Nutria also damage bald cypress and water tupelo forests, preventing them from regenerating by eating seedlings.

Ragondin (Myocastor coypu) gnawing tree, Ile de France, France
Gerard Soury / Getty Images

Because nutria breed prolifically and consume several pounds of vegetation per day, this damage happens quickly. In the early 2000s, researchers with Louisiana's Department of Wildlife and Fisheries estimated that nutria were damaging around 100,000 acres of wetlands per year. Following the institution of their bounty program in 2002, in which around 400,000 nutria per year are harvested, that damage is currently estimated at around 15,000 acres. Scientists were concerned that this many dead nutria might harm other native populations, namely the alligator, but found that the probability of an alligator stomach containing nutria in five south Louisiana parishes did not change regardless of whether or not nutria were being harvested nearby.

Many marshes invaded by nutria are prized for their ecological importance, like the Chesapeake Bay in eastern Maryland. Internationally recognized as valuable wetlands, these areas are not only important for fishing and hunting, as ecotourism increasingly plays an economic role. Lawmakers as well as advocates have long raised the alarm that marsh destruction as a result of the nutria will inevitably impact the hundreds of species of plants and animals native to these areas, leading to significant ecological, cultural, and economic losses.

Nutria feeding behavior destroys the root mat that cements the marsh together. After this network of fibers has been damaged, these areas are highly susceptible to erosion and can become muddy flats first and then, eventually, open water, which will not support the majority of the species that typically thrive in a marsh. Of course, nutria are not the sole source of coastal land loss, and the climate crisis will only exacerbate the types of damage nutria cause, as sea levels rise and these habitats are minimized.

Efforts to Curb Environmental Damage

Perhaps the most successful effort at curbing a local nutria population to date has been in Maryland — where a nutria control program successfully removed all of the known nutria from over a quarter million acres of the Delmarva Peninsula as well as the Chesapeake Bay. These efforts are considered "restoration through eradication" and are backed up with evidence showing that less nutria in an area means less marsh damage.

Nutria or Coypu, Myocastor coypus, in swamp, Louisiana, USA. Introduced from South America
John Cancalosi / Getty Images

Louisiana and Maryland both started nutria control programs in 2002, though the process and results have been different. In Louisiana, the private sector generally assumes the eradication effort, and trappers kill the nutria in exchange for a bounty of $6 per nutria. This program is meant to control the population and has effectively stopped its growth, though millions are believed to still live in the marshes. In Maryland, the USDA and partners assumed the role of capturing and removing the nutria with a goal of complete removal, eventually eradicating the known population. Similar efforts are underway in California to control growing nutria populations in certain areas.

For many environmentalists and sustainability-minded folks, control programs are a tough pill to swallow. There's a lot of waste involved in killing millions of fur-bearing, edible, creatures and subsequently burying or burning them. Efforts at reviving the use of nutria meat and fur have been around for more than a decade, in an effort to waste less and also potentially to create a new market for nutria, providing economic incentive to reduce the population. Chefs in New Orleans have posted recipes online, and a recently released film about nutria, Rodents of Unusual Size, highlights James Beard award winner Chef Susan Spicer as she prepares the rodent.

Another now-defunct New Orleans non-profit called Righteous Fur worked to connect trappers to local artists and designers, providing a use for nutria pelts and teeth (which can be used to make jewelry) that remained after trappers harvested the animal. The potential downside to these ventures? Efforts at marketing nutria are too successful and the problem begins anew as people are economically incentivized to farm the animal. Most people assume that won't be a problem, however, given the nutria's unsightly appearance and current lack of demand for fur in the United States.

Perhaps the most direct way to undo the nutria's damage is through marsh plantings, when volunteers replant grass and trees lost through nutria or boar damage, as well as coastal erosion. People living near areas with nutria damage, particularly south Louisiana, can reach out to local advocacy groups including the Coalition to Restore Coastal Louisiana to participate.

View Article Sources
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