Native to South America, the nutria is a large, semiaquatic rat that was brought to the United States in 1889 for its fur. Following a collapse of the nutria fur market in the 1940’s, thousands of nutria were released into the wild, endangering native aquatic vegetation, crops, and wetland areas in over 20 states across the US. Over the past 70 years, nutria populations have continued to spread rapidly throughout western Washington, with the species now appearing in eastern Washington. Below are ways to identify and protect the environment against the nutria population.
How to Identify: Commonly mistaken for a beaver or muskrat, nutria average about 2 feet long from nose to tail with adults ranging from 15 to 20 pounds. Nutria have a dark brown coat with 3 layers of fur varying in density. Their whiskers are about 4 inches long and they are known for their visibly large yellow/orange front teeth. An avid swimmer, they have partially webbed hind feet and eyes, ears, and nose set high on their heads to stay above the waterline. Glands located near the corners of their mouths produce oils that are used for grooming, while waterproofing the fur. Nutria can spend most of their time in water due to valves found in their mouths and nostrils that seal out water when submerged. Their ability to swim long distances and see underwater help them escape predators while traveling from place to place.
Spread: Nutria are quite prolific, producing up to 3 litters per year of 4 to 9 young. The species has a gestation period of 4 months, with females able to breed again 1 to 2 days after giving birth. Most nutria pups stay with their mother for 3 to 4 months, though pups can survive alone at 5 days old. Nutria breed throughout all seasons, with survival rates dependent on weather conditions and predators. Rapid growth in nutria populations result from the species’ few natural predators, with humans, bald eagles, and carnivorous mammals posing the largest risks. Nutria live in groups of 2 to 13 and reside in burrows near bodies of freshwater such as rivers, lakes, wetlands, and canals.
Impact: Nutria can have a devastating impact on ecosystems. Each day, nutria consume up to 25 percent of their body weight – eating mostly roots and stems of native plants. Thanks to their preference for roots, nutria destroy up to ten times more vegetation than they eat, destabilizing soil and speeding up erosion. Nutria can also cause bank collapse and erosion by constructing burrows in levees, dikes, and embarkments. This burrowing can also weaken the foundations of buildings, roadways, and dams, putting this infrastructure at risk for collapse. Nutria carry a host of diseases and parasites such as tapeworm, tuberculosis, and nematodes. These pathogens are a health hazard to humans as well as wildlife and domestic animals and can be carried through the water where nutria reside.
Prevention: Mitigation efforts can include fencing in plants, managing water levels, and installing embarkment barriers. Most importantly, the Washington Invasive Species Council advises citizens to report nutria sightings on their website to help them assess the species’ spread. In addition, property owners should contact a state-licensed trapper to capture and remove nutria when they are discovered on their property. Due to their danger to the environment, this species should not be relocated or transported within Washington State.