A Big Rat in Congress Helped California Farmers in Their War Against Invasive Species

The state faces a massive threat from invaders—like the nutria, a swamp rat from South America—that threaten crops and the environment.

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Nutria, an invasive rodent from South America, damage wetlands, levees and agricultural crops, Credit: Smith Collection/Gado/Getty Images
Nutria, an invasive rodent from South America, damage wetlands, levees and agricultural crops, Credit: Smith Collection/Gado/Getty Images

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California Rep. Josh Harder needed a way to convince the U.S. House of Representatives to pay attention to his speech about invasive species during a meeting in February. So he brought in a hefty rat carcass and laid it on the table next to him.

The taxidermied rat, which Harder called “Nellie,” convinced the House to unanimously pass a bill that supports eradication efforts in states infested with nutria, large rodents also known as swamp rats that are native to South America. 

“I think it was the first time in congressional history that a taxidermied swamp rat made an appearance on the House floor,” Harder, a Democrat, said. The bill, which will now go to the Senate, authorized the funding for efforts to fight the nutria. 


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The legislation would revise the Nutria Eradication and Control Act of 2003, which initially provided grants to Maryland and Louisiana, to expand nutria eradication efforts to about a dozen states, including California. The nutria has been established in 17 states

A spokesperson for Harder said it was unclear when the bill would be introduced in the Senate. He said the pandemic has slowed down the momentum behind the bill.  

If enacted, the legislation would provide $12 million for nutria eradication, and California would receive a substantial portion of that sum. The money would be an addition to $10 million allocated to California last year for an eradication team trained to tackle the species. 

In April, the eradication team put a tracking device in a neutered nutria to track where the rest of the animals are located. Harder said the initiative is working and since May, California has caught 1,000 of the rodents. But more federal funding is needed to make the program fully operational, Harder said. 

The nutria is one of the most recent invasive species to arrive in California and one of the most harmful. For the last year, the rodents have plagued California’s Central Valley region, posing risks to agriculture and the environment by eating up crops and polluting canals, Harder said. Even with the current pandemic and resulting economic downturn, California plans to spend millions to eradicate the nutria, and farmers are on high alert. 

With its diverse topography, more than 400 commodity crops and lucrative agriculture industry, California faces a massive threat from invasive species, and the state spends millions every year to mitigate their impact. As climate change shifts temperatures and seasonal conditions, the location of invasive species is shifting, as well. This creates difficulties for farmers and scientists trying to manage the pests, forcing them to find new methods and spend more money to combat newly arrived invaders.

The nutria, for example, are ravaging California’s Sacramento-San Joaquin Delta region, jeopardizing the area’s soil and its water, which are vital to the state’s economy and food supply. Harder said the swamp rats can set off flooding by destroying irrigation canals. The rats also consume colossal amounts of plants, algae and other organisms that absorb carbon dioxide. 

Harder’s goal is to eradicate the animals by 2025, potentially an arduous effort considering that one female nutria can produce more than 200 offspring in a year, he said. 

“If we don’t get this under control in California, there’ll be 250,000 of these giant 40-pound swamp rats within five years, which is a big deal,” he said. “And so one of the challenges here is making sure that we could make this relevant to every member of Congress.” 

California is no stranger to invasive species. Nearly 1,500 non-native pests have established themselves in the state, where a warm environment and a lack of predators encourage them to take up residency, according to the University of California Statewide Integrated Pest Management program. 

The spread of invasive plants is one of the biggest threats to the state’s vegetation, second only to habitat destruction, according to the California Department of Fish and Wildlife. Plant infestations can crowd out crops, increase the risk of wildfires and flooding, devastate the water supply, and in some cases can supplant entire plant communities. 

“Few areas have had their vegetation so completely altered as California’s Central Valley,” the department says on its website.

The California agriculture industry loses more than $3 billion a year as a result of invasive pests, according to the Center for Invasive Species Research at UC Riverside.

But Mark Hoddle, the center’s director, said this number may be an underestimate. To calculate agricultural damages, he said,  the loss of crop yield and the money that goes into eradicating pests—the cost of pesticides, for example—have to be factored in.  “All these costs start to compound,” Hoddle said. 

Slowly Evolving Climates

Climate change did not create the issue of invasive species. But shifting temperatures and changing environmental conditions are making the problem worse and pushing species into new areas of the state, said Daniel Sumner, director of the University of California Agricultural Issues Center. 

“Both more uncertainty and the slowly evolving climates will make pest control more costly and complicated in most places,” he said. “There may be places where invasive pressures are lessened but not most places in California.”

Surendra Dara, an entomologist at UC Cooperative Extension, said that if temperatures are warmer for longer periods of time throughout the year, that gives the species more time to reproduce and damage crops. 

“When it snows, then the populations crash and then restart in spring,” he said. “And when we don’t have those kinds of harsh winter conditions, even a one degree, two degree change could be ideal for the insects to not die and continue until climate change can worsen problems.”  

And California is warming. Temperatures in Southern California, for example, have increased about three degrees Fahrenheit in the last century, and the state’s snowpack has declined since the 1950s, creating conditions that encourage the introduction of new invasive species. Hoddle said the widely varying climate in California is one reason the state can accommodate so many non-native pests. 

“From very hot, dry out in the desert to cool and foggy along the coast to cool and rainy up in the northern parts of the state, there’s a lot of different environments that these invasive pests can slip into,” Hoddle said. 

Stephen Vasquez, a technical viticulturist at Sun-Maid Growers of California, said that in Fresno county, where he lives, the cold winters that would usually kill insects are warming, allowing the insects to persist even through the winter and reproduce earlier in the spring season. 

“Very early on, pests can start showing up, and that means that a grower has to think about managing the pest in a different way,” he said. 

Sumner said the temperature shifts are likely to make addressing the invasive species problem more difficult, driving out old species and welcoming in invasives that the region isn’t used to managing. In Yolo county in the north of the state, he said, climate conditions are becoming more like the counties further south. 

“There were pests that growers didn’t worry about here,” he said. “But now, we have to because we’re not getting as much freezing at night,” he said. 

An Economic Nightmare

Vasquez said he does not know the exact cost in agricultural losses to the grape industry from invasive species, but for an individual grower, the effects of a new non-native pest can be devastating. For example, if a farmer grows 80 tons of seedless grapes for raisins, an invasive species could affect 20 to 30 percent of that dried fruit, he said. 

“For us, as in the raisin industry, what happens is that fruit just gets left on and it never gets picked,” Vasquez said. “But because the pest is in those clusters, it can continue to grow throughout the rest of the season, and there’ll be some mating that goes on and then that impact continues into the next season.” 

In a state with an almost $50 billion agriculture industry, the economic impacts can be daunting. California produces over a third of the country’s vegetables and two-thirds of the fruit and nut supply. The state also accounts for 13 percent of the nation’s agricultural value. 

Grapes are California’s second most lucrative crop, producing $6.25 billion in revenue in 2018, according to the CDFA. 

Invasive species can also interfere with California’s agricultural exports,  including fruits, nuts and vegetables. Shipments from places where invasive species are harming crops are often refused by other countries, creating losses of up to millions of dollars for the grower, said Jim Farrar, director of the UC Statewide Integrated Pest Management Program. 

“When there’s a new invasive in the state, sometimes our trading partners look at that and say, ‘Well, we don’t have that invasive species, and we don’t want it so we aren’t going to continue trading in whatever crop is affected.’” Farrar said, adding that some of that was based on international politics, but “some of that is based on legitimate fear.”  

A Two-Way Highway 

Because of increased travel to California, the rate of new species of exotic pests entering the state each year increased over 50 percent from 1989-2010, jumping from six to over nine a year, according to CDFA study. A third of those new species were harmful to the economy or the environment. 

Insect species, in particular, can disperse rapidly and widely by attaching themselves to traveling vehicles and to products exported across state lines or internationally. The marbury stink bug, for example, started out as a Pennsylvania problem but then spread throughout the country by hitchhiking on cars and trucks, said Jayson Harper, director of Penn State University’s Fruit Research and Extension Center. 

Invasive species are also often introduced to the rest of the United States from California, according to Farrar, because that is where the international trade ports are. He said border inspections at these ports are the most cost effective way to manage invasive species because it is less expensive to perform inspections than to deal later with the pests. 

Other invasive species that California officials are on the alert for include the spotted lanternfly, which has ravaged its way across the Northeast, causing millions in agricultural damage; the Asian citrus psyllid, a long-time threat to California’s $3 billion citrus industry, and the vine mealybug, which harms the grape industry by spreading diseases and infiltrating clusters of table grapes. 

The Asian citrus psyllid. Credit: USDA ARS Image Gallery
The Asian citrus psyllid threatens California’s citrus industry. Credit: USDA ARS Image Gallery

Vasquez said the vine mealybug, in particular, has been a problem for them and for the entire grape industry because it is not affected by many pesticides. Instead growers have resorted to trying to disrupt mating in the mealybug or releasing its natural enemy to control the population.  

Sumner said experts have studied the parallels between the spread of Covid-19 and invasive species to increase understanding of exotic pest prevention. “It’s their job to think about the dangers of interaction,” he said. 

He said in order to prevent exotic pests from entering the state, California would have to close borders to trade and travel, just as with Covid-19, but the massive blow to the economy that closure would cause has prevented the state from doing that.  

“There’s a balance here and the economists come in and try to help calculate the balance. In every one of these issues, and climate highlights this, it’s always the case,” he said.

He said when experts address a threatening invasive species, they consider the same questions that epidemiologists do when it comes to Covid-19. 

“Just like in the Covid-19, we know how damaging it is, how quickly it spreads, how costly it is to root it out once it gets here.”

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