20-Pound Rodents Invading California, Officials Warn

CALIFORNIA -- State officials this week warned the public about large swamp rodents that have been spotted, and are reproducing in California. If the rodents, known as nutria, reproduce, they can "severely impact California’s resources," officials with the Department of Fish and Wildlife said.

Officials said the rodents have been found in wetlands, rivers, canals and other freshwater habitat in Merced, Fresno and Stanislaus counties.

"If allowed to establish, nutria will severely impact California’s resources, causing the loss of wetlands, severe soil erosion, damage to agricultural crops and levees and reduced stability of banks, dikes and roadbeds, as they have done in Louisiana, Chesapeake Bay and the Pacific Northwest," officials said in a press release. "Nutria also degrade water quality and contaminate drinking supplies with parasites and diseases transmissible to humans, livestock and pets."

"Given the severity of potential impacts and the impacts realized in other infested states, CDFW believes early intervention actions could be successful in eradicating nutria from the area and is asking the public’s help in looking for and reporting nutria sightings in order to determine the extent of the infestation."

The full extent of the infestation is not yet known.

The rodents can reach up to 2.5 feet in body length, 12-inch tail length and 20 pounds in weight. Nutria strongly resemble native beaver and muskrat, but are distinguished by their round, sparsely haired tails and white whiskers. They are native to South America.

Female nutria are reproductive by six months of age, breed year-round, and can produce three litters in 13 months. Within approximately one year of reaching reproductive maturity, one female nutria can result in more than 200 offspring, which can disperse as far as 50 miles, officials said.

"Nutria are destructive, wasteful feeders that destroy up to 10 times the vegetation they consume," officials said.

Since March 2017, more than 20 nutria, including males, pregnant females and juveniles, have been documented within private wetlands near Gustine, duck clubs, the Merced River near Cressey, adjacent to the San Joaquin River near Grayson, south of Dos Palos, the San Luis National Wildlife Refuge, and Salt Slough on the San Joaquin River.

Officials are currently preparing an eradication plan, the first stage of which is determining the full extent of the infestation. Assistance from local landowners and the public is critical to successfully delineating the population, they said.

Suspected observations or potential signs of nutria should be photographed and immediately reported to CDFW’s Invasive Species Program online, by e-mail to invasives@wildlife.ca.gov, or by phone at (866) 440-9530.

--Photo via Joyce Gross, UC Berkeley/California Department of Fish and Wildlife