Michael Fitzgerald: Worst. Invasive. Species. Ever.

Nutrias were first discovered in the marshes of San Joaquin County in 2017. (Photo courtesy of Greg Gerstenberg/California Department of Fish and Wildlife)

There’s news from the front lines of the battle against the nutria, the weird invasive “giant swamp rat” that threatens to overrun and destroy the Delta: We’re losing. 

The California Department of Fish and Wildlife doesn’t say that, of course. But its own data clearly show the population and range of the voracious South American beaver-like rodent are expanding towards a tipping point where they will be too numerous and widespread to eradicate. 

“It’s scary. It’s really scary,” said Jen Fox, a spokesperson for Congressman Josh Harder, D-Tracy.

Harder’s bill to continue funding nutria eradication efforts recently passed the House.  

“Nutria might look cute to some, but these giant swamp rats and their nacho cheese teeth are dangerous and they’re causing serious damage,” Harder said in a press release. 

Nacho cheese teeth: that’s a new one. But the threat has been clear since the nutria’s latest incursion into California was discovered around Merced in 2017.

Nutria (Myocastor coypus; the name literally means “mouse beaver,” though they average 15 pounds and can swell to 30) is a plant-eating semiaquatic rodent from South America. Fur traders introduced them to America. When the fur trade didn’t pay, some traders set them free. Nutria bored into riverbank burrows, emerging at twilight with dexterous digging forelimbs and oddly orange front teeth to uproot and devour great quantities of the vegetation that holds wetlands together, leaving open water. 

Nutria also bite humans, poop in the water, spread parasites to humans, and spread diseases such as rabies. 

I know it’s a weird subject. It’s also serious. They will destroy the Delta if unchecked.

Along the Amazon River, and other South American habitats, nutria populations are controlled by predators: jaguars, alligators, bald eagles, turtles, cottonmouth snakes, even garfish. None of these predators exist in the Delta.

And a female nutria can bear 200 offspring a year.

Given the birth rate, and their range, which has expanded to two million acres of riverine California, it is not surprising that the state has its hands full eradicating the nutria. 

“We have about 40 to 50 staff with boots on the ground from Suisun Marsh all the way down to Millerton Lake,” said Krysten Kellum, a public information officer with the Department of Fish and Wildlife. “We have cameras in place seven days a week from the Delta all down the San Joaquin corridor, over 1,000 cameras.”

And many traps. It’s good work, but it’s not enough. Nutria are growing in number and gnawing their way into ever more waterways.

From 20 nutria “taken” (trapped and/or killed) in 2017, the number rose to 5,171 in 2024. There’s two ways to read that: state efforts are increasing; nutria are increasing. DWR’s own map removes any doubt. The destructive rodents have spread up and down Central Valley rivers.

“They’re not doing enough,” Barbara Barrigan Parilla of Restore the Delta said of state efforts.

She opined why. “The reason why they’re not doing enough is the same reason we have levee failures this year: anything that involves restoring, fixing and maintaining the Delta is grossly underfunded.” 

The state views the Delta primarily as a place to grab water, Barrigan Parilla said, while problems like levees, nutria, and toxic algae blooms never get adequate treatment.

“We’re seen as an extraction region, regardless of how much we advocate,” she said, “and everything is related to the tunnel,” the Delta Tunnel project to bypass the Sacramento-San Joaquin Delta and move water to Southern California. “Real efforts to fix problems are underfunded.”

One Restore the Delta staffer calls this under-action “weaponized incompetence,” letting the Delta languish to further the state’s […]

Full article at Stocktonia