Nutria

• 1. Introduction

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  Sheriff Harry Lee of Jefferson Parish, Louisiana, once sent SWAT sharpshooters after the nutria, a plant-eating rodent from South America. The animal is also called the coypu, and its scientific name is Myocastor coypus. It lives in burrows beside rivers and marshes and feeds on the stems of water plants. Fur farmers carried it to North America, Europe and Asia, and in several countries it is now classed as an invasive species. Why would a rodent that eats plants call for police marksmen? How did an animal from South America end up in Louisiana, Japan and Ireland? And what, if anything, has actually managed to remove it?

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• 2. Names and Family Tree

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  The genus name Myocastor joins two Ancient Greek words, one for a mouse or rat and one for a beaver, so it literally means mouse-beaver. English speakers cannot agree on what to call the animal. In North America, Asia and the countries of the former Soviet Union, it is the nutria, from the Spanish word for otter. That choice causes confusion in most Spanish-speaking countries, where nutria mainly means an otter. South America, Britain and other parts of Europe therefore favor coypu or coipo, which comes from Mapudungun.

  Other languages have their own versions. The French say ragondin. Dutch speakers say beverrat, which means beaver-rat. Germans use Nutria, Biberratte or Sumpfbiber, meaning swamp-beaver. Italians also say nutria, yet they call its fur castorino, or little beaver. Swedes say sumpbäver, a marsh beaver. In Brazil it is ratão-do-banhado, meaning big swamp-rat, or nútria, or caxingui, a word borrowed from Tupi.

  Scientists have been just as inconsistent. Juan Ignacio Molina first described the animal in 1782 as Mus coypus, which placed it in the mouse genus. Robert Kerr assigned the genus Myocastor in 1792. Geoffroy Saint-Hilaire, working independently of Kerr, named it Myopotamus coypus, and that name still appears occasionally. For a long time the nutria was the only member of its own family, Myocastoridae. It now sits inside Echimyidae, the family of spiny rats. Comparisons of DNA and protein sequences show that its closest relative is Callistomys, the painted tree-rats.

  Four subspecies are generally recognized. M. c. coypus lives in central Chile and Bolivia, and M. c. melanops is found on Chiloé Island. M. c. bonariensis ranges from northern Argentina through Paraguay and Uruguay to southern Brazil. As the northernmost, subtropical form, it is believed to be the type most often introduced to other continents. The fourth, M. c. santacruzae, belongs to Patagonia.

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• 3. Orange Teeth, Fast Litters

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  Adult nutrias typically weigh 4 to 9 kilograms and measure 40 to 60 centimeters in body length, with a skinny, hairless tail of 30 to 45 centimeters. Most adults average between 4.5 and 7 kilograms, though a few reach 16 or 17. The animal looks like a very large rat, or a beaver with the wrong tail.

  Three layers of fur cover the body. Guard hairs on the outer coat are three inches long. Beneath them lies a coarse, darkish brown midlayer, and beneath that a soft, dense grey underfur, which is also called nutria. A white patch on the muzzle and webbed hind feet help identify the animal. So do the large, bright orange-yellow incisors. The orange comes from iron in the tooth enamel. Nutrias have about 20 teeth, and the four big incisors never stop growing. Whiskers on each cheek reach four inches. Females carry their mammary glands high on the flanks, so the young can feed while the mother floats in the water.

  People often confuse the nutria with the muskrat, Ondatra zibethicus, which shares its wetlands. The muskrat is smaller, copes better with cold and has a tail flattened from side to side. The nutria's tail is round. A small beaver is another easy mistake, since beavers have very similar anatomy and habitats. Beavers have flat, paddle-like tails.

  A wild nutria rarely lives past three years, although captive animals can reach six. One study found that 80% die in their first year and fewer than 15% of a wild population is older than three. Four years counts as old age. Breeding makes up for the losses. Females can be mature at three months and males at four, though adolescence sometimes lasts until nine months.

  Gestation takes 130 days, and a litter can hold as few as one pup or as many as 13. The average is four. Mothers line nursery nests with grasses and soft reeds. Pups are born fully furred with open eyes, and within hours they can eat vegetation and swim alongside their parents. A female can become pregnant again within a day or two of giving birth. She typically has two litters a year, and six in a lifetime, rarely seven. Young nurse for seven to eight weeks before leaving their mothers.

  Nutrias can be territorial and aggressive when cornered, and they will bite people and dogs. They are mostly active at dusk and after dark, with the peak around midnight. When food is plentiful they rest and groom through the day. A nutria seen foraging in daylight may therefore be a hungry one.

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• 4. Dens, Diets and Winters

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  A single nutria eats about 25% of its body weight every day, and it feeds all year. It bites off the base of above-ground stems and digs through soil for roots and rhizomes. In winter it turns to tubers and the bark of black willow trees. The menu includes cattail, rushes, reeds, arrowheads, flatsedges and cordgrasses. Farm crops are also fair game, among them lawn grasses, alfalfa, corn, rice and sugarcane.

  Freshwater marshes and wetlands are the usual home, with brackish marshes next and salt marshes only rarely. A nutria digs its own burrow or moves into one that a beaver, muskrat or other animal has abandoned. Dens sit partly underwater, but the main chamber stays above the waterline. Nutrias can also build floating rafts from vegetation. They live in colonies, and one male typically shares a den with three or four females and their young. For dining, they build feeding platforms from cut plants laid over a log or branches, and they often borrow muskrat dens and beaver lodges for the same purpose.

  The native range covers Chile, Argentina, Uruguay, Paraguay and the southern parts of Brazil and Bolivia. Abroad, the limit is set by cold. Frostbite on the tail can lead to infection or death during hard winters. In the 1980s, populations died out locally or regionally in the Scandinavian countries and in the U.S. states of Idaho, Montana and Nebraska. Mild winters push the range north again, and in recent years it has grown in Washington, Oregon and Delaware. Forecasts say the nutria will keep moving northward over the next century as global temperatures rise.

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• 5. Fur Farms and Escapes

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  The first attempt at nutria farming came in France in the early 1880s, and it was not much of a success. The idea grew from a shortage. Overharvesting had wiped out nutria in parts of their native range, so fur farms appeared in the late 19th and early 20th centuries. Argentina had the first ones, followed by Europe, North America and Asia. The first efficient, large-scale farms opened in South America in the 1920s and did very well, which inspired similar farms on other continents.

  Most of those farms failed as long-term investments. As operations lost money, farmed animals escaped or were set free. Some releases were deliberate, meant to create a game animal or to clear aquatic vegetation from waterways.

  The U.S. Geological Survey says nutrias first reached the United States in California in 1899, brought by William Franklin Frakes. Louisiana imported them in the early 1930s for the fur trade. Trapping pressure from fur traders kept their numbers small for a time. At least one Louisiana farmer released nutrias in 1933. E. A. McIlhenny later released his entire stock on Avery Island in 1945.

  A hurricane then did what the farmers had not. When a storm hit the Louisiana coast in the early 1940s, it destroyed the enclosures, and the animals spread through coastal marshes, inland swamps and other wetlands. Texas contributed too. The Louisiana Department of Wildlife and Fisheries says nutrias were moved from Port Arthur to the Mississippi River in 1941 and spread further after a hurricane later that year. From Louisiana they moved across the southern United States.

  An ocean away, East Anglia received nutrias in 1929, again for fur. Many escaped and damaged the area's drainage works. Once demand for the fur fell, nutrias lost their commercial value, and the animals that remained were treated as pests.

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• 6. Marshes and Microbes

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  On plots open to nutria feeding, researchers in Louisiana found 40% less vegetation than on fenced plots. Alone, that loss is not a serious cause of land disappearing. Combined with another disturbance, such as fire or repeated clearing of plants to simulate a tropical storm, the damage multiplied. Nutrias also make "eat-outs", patches where most of the plant material above and below ground is gone. Fire and storms strike once or a few times a year, but nutrias feed constantly, and they do the most harm in winter, when little grows above the surface and they dig up root networks.

  Fertilizer made matters worse. When researchers fertilized open plots, the plants did not recover. Nutrias fed more heavily there, and extra nutrients simply produced more nutrias. The marshes matter. The U.S. Fish and Wildlife Service found that wetlands cover only 5% of the contiguous 48 states yet support 31% of the nation's plant species. They shelter migratory birds, filter water, reduce flooding and protect against storm surge. Louisiana already loses about a football field of wetland every hour.

  In 1998, the Louisiana Department of Wildlife and Fisheries ran the first coast-wide aerial survey, called the Nutria Harvest and Wetland Demonstration Program. It found roughly 90,000 acres of herbivory damage. A repeat survey a year later put the figure near 105,000 acres. In Maryland's Blackwater National Wildlife Refuge, nutria introduced in the 1940s are believed to have destroyed 7000 to 8000 acres of marsh by eating plant roots. By 2003, a multimillion-dollar eradication program was underway there. In Louisiana, nutrias also chewed through tires and wooden house panelling and eroded river banks.

  The animals carry health risks as well. A roundworm they host can infect human skin and cause a rash called nutria itch. They also harbor tapeworms, liver flukes and blood flukes, along with fleas, ticks and lice. Urine and feces contaminate the water. Nutrias are reservoirs for salmonellosis, encephalomyocarditis virus, Chlamydia psittaci and antibiotic-resistant Aeromonas bacteria, among other diseases. According to the CDC, they carry two of the eight diseases of concern for the United States, rabies and salmonellosis. Nutrias live on every continent except Australia and Antarctica, and local awareness of these diseases will matter more as climate change progresses.

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• 7. Bounties and Menus

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  Louisiana placed its first bounty on nutria in 1958, but the effort was never funded. Damage had been severe enough to draw lawmakers' attention since the 1950s. Real payments began in 2002 under the Coastwide Nutria Control Program, which also receives money from the Coastal Wetlands Planning, Protection, and Restoration Act.

  A licensed hunter or trapper may catch an unlimited number of nutrias. Each catch is proven by its tail, which is cut off and handed to an official of Coastal Environments Inc. at an approved site. In the first year, 2002-03, 308,160 nutrias were harvested and incentive payments totaled $1,232,640. By 2019 each tail was worth $6, up from $4 before the 2006-07 season. In 2009-10, hunters turned in 445,963 tails worth $2,229,815.

  The officials also record the number of tails per person and parish, the capture method and the location. That information goes into a database, which estimates nutria density along the coast. State biologists combine it with aerial surveys to judge how many nutrias remain and how much damage they cause. By the department's estimate, affected wetlands fell from a minimum of 80,000 acres in 2002-03 to about 6,296 acres in 2010-11. The department stresses that coastal restoration projects will struggle without sustainable nutria control.

  Some of the rodents end up on plates. In 1997 and 1998, Louisiana urged the public to eat nutria and distributed recipes. The meat is lean, and it has less fat and cholesterol than ground beef. Poor and rural Louisianans had trapped and eaten nutria for decades. In Kyrgyzstan and Uzbekistan, people raise them on private plots and sell them in local markets as a poor man's meat. A Moscow restaurant, Krasnodar Bistro, has served nutria as a burger, hot dog and dumplings since 2016, and the flavor falls between turkey and pork. In Baton Rouge, the company Marsh Dog turns nutria meat into dog treats. It won a grant from the Barataria-Terrebonne National Estuary Program, and in 2012 the Louisiana Wildlife Federation named it "Business Conservationist of the Year".

  Better-sounding methods have stalled. Zinc phosphide is the only rodenticide registered for nutria, but it is expensive and stays toxic for months. Rain and high humidity break it down, and it needs floating rafts to hold it. Birds and rabbits have died from eating it, so it is rarely used. Testing a new chemical would cost an estimated $300,000 for laboratory and field studies, plus $500,000 for an Environmental Impact Statement. Birth control is the other option, with bait costing an estimated $6 million a year. Testing a contraceptive would take five to eight years and $10 million, with no guarantee of FDA approval.

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• 8. Eradication Abroad

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  Great Britain won the war that Louisiana is still fighting. Nutrias there were reported in the wild as early as 1932, and three attempts to control them in East Anglia in 1943 and 1944 failed. By the 1950s they were damaging farms. In the 1960s, a grant to rabbit clearance societies was extended to cover nutria, and 97,000 were removed in 1961 and 1962. From 1962 to 1965-12 trappers confined the remaining animals to the Norfolk Broads. Their live traps let other species go free, and any nutria caught was shot. With help from the cold winters of 1962 and 1963, almost 40,500 nutrias were removed.

  Numbers rebounded after that campaign ended, so a new one began in 1981. Trapping areas were divided into eight sectors, leaving no ground uncontrolled. The 24 trappers were offered an incentive to finish the 10-year campaign early. Only three nutrias, all male, turned up between 1987 and 1989, and the animal was assumed eradicated in 1989.

  Maryland followed a similar path. On the Delmarva Peninsula, between Chesapeake Bay and the Atlantic Coast, nutrias once numbered in the tens of thousands. The eradication program there had nearly succeeded by 2012. In September 2022, officials announced that nutrias were completely gone from Maryland's Eastern Shore.

  California is borrowing that playbook. Nutrias were recorded in the Central Valley and on the south coast in the 1940s and 1950s, but they had been wiped out statewide by the 1970s. They returned in Merced County in 2017, near the San Joaquin River Delta. Officials worry about the infrastructure that sends water to farms and cities. In 2019 the state wildlife department received nearly $2 million in Governor Gavin Newsom's first budget, plus $8.5 million via the Delta Conservancy over three years. The plan includes the "Judas nutria": a captured animal is sterilized, fitted with a radio collar and released, and hunters then track it back to its colony. Trained dogs help, and the state has dropped its earlier no-hunting policy, although a license is required. Bounties are not advised there because hunters could mistake native muskrats and beavers for nutrias.

  Japan has had less luck. Nutrias arrived in 1939, imported from France during World War II to ease food shortages and supply fur. After the war, in 1950, many were released en masse or escaped. They became one of the country's worst invasive species, damaging river banks, rice fields and other crops. An eradication program launched in 1963 has shown little to no success, and the Invasive Alien Species Act of 2004 restricts importing, transporting and keeping them.

  Ireland is at an earlier stage. The first wild nutria was sighted there in 2010. In 2015, some escaped from a pet farm in Cork City and began breeding on the city's outskirts. Ten were trapped on the Curraheen River in 2017, yet the animals kept spreading and reached Dublin along the Royal Canal in 2019. That year the National Biodiversity Data Centre had already issued a species alert, saying the animal "has the potential to be a high impact invasive species in Ireland."

  Italy brought nutrias in during 1928 for fur farming. Many escaped or were freed when fur fell out of fashion, and they are now found mainly in central Italy and the Po Valley. Michele Marchi, the mayor of Gerre de' Caprioli, suggested that people could reduce the population by eating them. Since 2016, the European Union has listed the nutria among its Invasive Alien Species of Union concern. It may not be imported, bred, transported, sold or deliberately released anywhere in the EU. New Zealand goes further and classes it as a "prohibited new organism" under its Hazardous Substances and New Organisms Act 1996, so it never arrives at all.

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