Some of America's most rat-infested cities are trying rodent birth control. Will it work?

Sarah Elbeshbishi, USA TODAY
·3 min read
9

After California and other states restricted the use of highly toxic rat poisons, cities have turned to a new method to try to control their rat populations: birth control.

Rather than a pill, the contraceptive, known as ContraPest, is deployed in bait boxes as a liquid that is high in fat and water content and targets their reproductive capabilities, preventing them from contributing to the population.

“The problem is that rats reproduce at an incredible rate,” said Ken Siegel, CEO of SenesTech, a biotechnology company that produces ContraPest. “You just can’t kill them fast enough to offset that reproduction rate. And so ContraPest is really the only solution that’s out there that deals with the second half of the equation, which is birthrate.”

Just two sexually mature rats could account for about 15,000 rats within a year, according to Siegel. Once consumed, the liquid contraceptive leaves rats infertile for about 100 days, preventing them from producing offspring.

San Francisco and Los Angeles – which are both among the top five “rattiest” cities in 2021, according to Orkin’s annual report – started using ContraPest as a method of pest management after California banned the use of second-generation anticoagulant rodenticides. Those include familiar brand names such as d-Con, Hot Shot and Talon.

Anticoagulant rodenticides thin blood to prevent it from clotting, causing a rat to die from internal bleeding. The same fate befalls other animals that encounter the poison, whether they eat the rat or get exposed through some other means, according to the British Columbia Society for the Prevention of Cruelty to Animals.

ContraPest was found to help decrease rat populations by more than 90%, based on studies at various locations, including in Washington and a poultry facility in California, according to Brandy Pyzyna, vice president of research and regulatory affairs at SenesTech.

The contraceptive works in conjunction with other measures, including traps and eliminating potential food sources.

The San Francisco Recreation and Parks Department has used ContraPest since 2019, ensuring there isn’t a sanitation issue, reducing vegetation that might harbor rats and monitoring and trapping rats when necessary, according to Tamara Aparton, the department’s spokesperson.

“It can be really effective if other food sources have been eliminated,” Aparton said. “But if rats are feeding on a steady supply of food waste, they’re going to be less tempted by the reproductive bait and not ingest a large enough dose.”

As states and cities restrict the use of rodenticides and other poisons to prevent harming other wildlife, more municipalities look to incorporate the liquid contraceptive.

“We’re now starting to see deployments in Columbus, Ohio; in Harford, Connecticut; suburban Boston,” Siegel said. “Every time that we announced that we’re doing something in one of those locations, we start to get inbound inquiries from the adjacent towns and cities. So it’s starting to accelerate.”

While the interest in ContraPest grows, traditional methods of controlling rat populations remain the norm.

“I think in the pest control industry, at least in the U.S., the idea of fertility control, they’ve heard about it, but it’s not widely understood why it’s beneficial,” Pyzyna said. “It does take a lot of education to explain to people why you wouldn’t just kill.”

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This article originally appeared on USA TODAY: Rat birth control used to manage rodent population in American cities