Nutria: The Invasive Rodents of Unusual Size

By Rachel Ross - Live Science Contributor 7 days ago

Reference Article: Facts about nutria.

Nutria, known as coypu or swamp rats, are large rodents that live in areas with lots of freshwater. 

These mammals are native to South America and were introduced into the United States between 1899 and 1930 through the fur industry, according to the U.S. Fish and Wildlife Service (FWS). Nutria are now considered a nuisance in the U.S. and other parts of the world where their populations have grown and their presence has disrupted the native ecosystem. 

What are nutria? 

Nutria (Myocastor coypus) are relatively big rodents that grow to between 17 and 25 inches long (43 to 64 centimeters) from head to rump, which is about the same size as a raccoon. Their tail adds another 10 to 16 inches (25 to 41 cm) and the animals weigh between 15 and 22 pounds (7 to 10 kilograms), according to National Geographic. Although they're about the size of a raccoon, nutria look more like a cross between a small beaver and a giant rat, with two large, orange front teeth and long, rounded tails. 

Nutria breed year-round and can have up to three litters a year with between two and 13 offspring per litter, allowing their populations to rapidly grow, according to the California Department of Fish and Wildlife (CDFW). These mammals become sexually mature as early as 4 months of age, and females can breed again about 1 to 2 days after giving birth, according to U.S. Fish and Wildlife Service (FWS). After a gestation period of about 4 months, nutria pups will nurse for about 7 to 8 weeks and stay with their mom for around 10 weeks, but pups can also survive on their own when they're as young as 5 days old.

Nutria are aquatic creatures and prefer freshwater to saltwater. They live in burrows connected by tunnels that they dig near rivers, canals, lakes or in wetlands, according to National Geographic. 

These animals live in groups that typically consist of two to 13 individuals, according to the University of Michigan Museum of Zoology's Animal Diversity Web. The group often includes related adult females, their offspring and a single adult male. Young adult males are usually solitary, but don't often wander far from where they were born. Males have a home range of about 14 acres, while females stay even closer to home, keeping within about a 6-acre radius.

It's estimated that up to 80% of nutria don't survive their first year, and those that do survive, only live for two or three years, according to FWS. However, nutria in captivity may live up to about 12 years, according to Oregon State University.

Nutria have a voracious appetite for wetland plants and will chow down an entire plant — roots, bark and all, according to Animal Diversity Web. The furry rodents will occasionally eat small invertebrates such as insects and snails, according to FWS. But nutria aren't considered picky eaters as they're often caught eating crops such as rice, sugarcane and corn.

Why nutria are a problem

Nutria are native to the marshes and coastal lakes in Bolivia and Southern Brazil, according to Columbia University. Their populations in those locations are kept in check by the seasonal drought-flood cycles. Periods of drought decimate their population, but thanks to their rapid reproduction rate, the nutria are able to recover during the flooding season. 

In the 1800s, fur traders brought nutria to the U.S. so that the animals could be easily harvested for their thick and soft undercoat of fur. But when the fur market collapsed in the mid 1900s, many nutria farmers couldn't afford to keep their animals and released them into the wild.

The nutria not only survived, but thrived in their non-native homes. Today, nutria populations are found across the U.S., primarily in the coastal states, according to FWS. They're also an invasive species in Europe, Asia and Africa due to fur-farm escapees, according to the Global Invasive Species Database.

Nutria are now considered one of the most ecologically harmful invasive species on the planet.

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