Photograph by Yva Momatiuk and John Eastcott, Minden Pictures/National Geographic
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A nutria emerges from a swamp in Lake Martin, Louisiana.

Photograph by Yva Momatiuk and John Eastcott, Minden Pictures/National Geographic

Rodents of Unusual Size Invading U.S. Wetlands

The invasive species can grow as large as 20 pounds and has large buckteeth. 

Two hundred years ago, you probably wouldn't have been able to find them outside of South America.

But since then, nutria, a giant rodent that can grow larger than 20 pounds, has taken hold in the U.S.

California is the latest region to be plagued by the large, buck-toothed, web-footed rodent. Earlier this month, the state's fish and wildlife department issued a warning about the influx of nutria.

Breeding populations have recently taken hold in the San Joaquin Valley, just east of San Francisco.

"This is a very significant threat in terms of the environmental damage and our agriculture industry," says Peter Tira from the California Department of Fish and Wildlife. In recent months, he's been out in the field, setting up camera and regular traps to catch nutria in action.

"It's a very frightening situation in terms of impact."

When nutria are introduced into the environment, they can quickly raze the landscape, eliminating a host of important flora.

Wildlife officials first noticed the problem in March 2017, when they trapped a single nutria. Upon performing a necropsy (the animal version of an autopsy), they discovered the animal was a female—and she was pregnant.

Tira confirms they're spreading. Just this past week, one was spotted in a fourth county, meaning their geographic range is growing in California.

Where Did They Come From?

Before 2017, nutria hadn't been spotted in California in 50 years.

The California populations, like all others in the U.S., were imported in the late 19th century as part of the fur trade.

They first took hold when they were brought to Avery Island, a swampy coastal part of Louisiana 30 miles south of Lafayette and the production site for Tabasco brand hot sauce.

Many were bred and kept in fur farms or released and regularly trapped. Then the fur industry crashed. No longer able to maintain facilities, hundreds of nutria were released into the wild.

Where Did They Go?

Once free from fur farms, they began breeding—and breeding.

Nutria are such prolific breeders that one female can lead to 200 offspring in just a year, says Tira.

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Unlike animals that take a year or longer to reach sexual maturity, nutria are ready to make babies at about four to six months. Females have anywhere from five to seven babies in a litter, and they have several litters every year.

They've become a nuisance along the Gulf Coast, in the Chesapeake Bay, and in the northwest, but by far Louisiana has borne the brunt of the invasive species.

The animals thrive in marine environments and quickly spread through rivers into coastal wetlands.

At its peak, Louisiana had as many as 6,000 nutria per square mile.

Environmental Damage

There are several ways nutria damage sensitive environments.

One of the worst is the way they consume flora. Rather than just chomping on leaves, they eat the entire plant, including the roots, which means it's less likely to grow back.

"Where you have this rich mosaic of plants and trees, it converts rather quickly to open water," Tira says. In California, where more than 90 percent of the region's wetlands have been destroyed by development, any loss has lasting impacts.

Nutria also pose a risk to agriculture production, and their burrowing can cause infrastructure damage. In Louisiana, they weakened drainage canals and levees. Tira fears they could do the same in California.

Stopping the Spread

Abatement measures range in scale and creativity.

In the early 2000s, Louisiana's wildlife department tried encouraging people to eat nutria by asking chefs to create recipes inspired by the rodent.

There was even a campaign to bring their fur back in fashion, including the tagline: "Look fabulous while helping to save the wetlands."

Taking a more direct approach, Maryland's wildlife department staged an eradication project in which tens of thousands were removed from the wetlands over a 15-year period. None of the rodents have been documented since.

Tira says California is currently trying to catch as many as possible and is asking people to call officials when they spot one. Should the problem worsen, Maryland, he says, may serve as a model.