Ground Squirrels Invading CA After Poison Ban, Exterminator Says

CALIFORNIA — Ground squirrels like tater tots.

Zachary Smith, of Smith's Pest Management, learned about their prediliction for potatoes when he spent more than a year working at an elementary school in Castro Valley, where the rodents would steal tots right off the table while children were eating.

“They’re very comfortable around people once they get used to people,” he said. “They’re not a tame animal and people shouldn’t be interacting with them like this.”

The unappetizing story could become more common, according to Smith, in the wake of a new law that further restricts methods exterminators can use when combatting rodents.

The California Ecosystems Protection Act of 2023, also known as Assembly Bill 1322, was approved by Gov. Gavin Newsom last October and bans diphacinone, a first-generation anticoagulant rodenticide. Assemblymember Laura Friedman, D-Burbank, introduced the legislation because poisoned rodents are often eaten by other wildlife, harming the food chain.

Diphacinone is the first-generation anticoagulant rodenticide that is most often found in wildlife that is not its target, according to Friedman’s office, which noted the poison was found in about 30 percent of blood samples and 40 percent of liver samples tested during a 16-year study of urban bobcats in Los Angeles. Exposure can be fatal and cause severe skin diseases and lowered immune system response, according to the assemblymember’s office.

“Anyone who has seen the suffering of mountain lions or spotted owls from rodenticide poisoning knows how heart-breaking this is,” J.P. Rose, Urban Wildlands policy director at the Center for Biological Diversity, said in a news release from Friedman’s office. “Both people and wild animals are at risk, so putting restrictions on the deadliest rat poisons is the least we can do for our family members and the wildlife we hold dear.”

Exterminators have multiple ways to fight most rodents, according to Smith, but the rodenticides affected by the new law were the main tool against ground squirrels. The sole remaining effective legal rodenticide for the animals can only be used 50 feet or more from structures, he said.

That means ground squirrels can burrow under buildings and fences, unimpeded by poison, risking soil erosion and destablilized foundations, according to Smith, who said the rodents are also the primary vector of plague in California.

“The slow and tedious and extremely expensive method is to trap them one by one or in small batches,” he said, noting ground squirrel infestations often number in the hundreds or thousands, making a trap-and-kill approach cost prohibitive.

Smith has seen a significant increase in job requests involving ground squirrels following the law's approval and he expects that trend to continue. The rodents have no major natural predator and can accommodate extreme temperatures, he said, adding he believes there are already hundreds of millions in the state.

“They are the most difficult pest we deal with and that bait was the solution,” he said. “It’s a little scary.”