Finding an Alternative to Rodenticide: Use a Better Mousetrap

A gray-colored black rat climbs down rocks.
Black rat (rattus rattus). © 2004 Larry Jon Friesen

Recent news that California will remove second-generation rodenticides from the consumer market was welcome at the California Department of Fish and Wildlife (CDFW). Unfortunately, some consumers concluded that they would soon have no way to keep “disease-ridden vermin” away from their homes. That is not the case.

The Department of Pesticide Regulation (DPR) is only restricting consumers’ access to rodenticides whose main active ingredients have caused the most illness and death to non-target wildlife and pets. (Trained, certified applicators will still be able to use the restricted products when necessary to control rodents.) The four chemicals subject to new regulations are known to have caused hundreds – probably thousands – of unintended animal deaths. They also poison more than 10,000 American children each year, according to the American Association of Poison Control Centers. A primary cause of these tragedies is misuse by consumers – failure to read and follow label directions.

“The best way to keep rodents out of your home, garage or any building is by blocking all the access points rats and mice may use to enter,” said CDFW Environmental Scientist Stella McMillin. “It can be as easy as stuffing steel wool into small holes or using a canned foam filler like ‘Great Stuff’ sold at hardware stores.”

Remove things that attract animals, especially food sources such as pet food or children’s snacks, that are left outside or accessible to rodents indoors. Rodents aren’t the only critters food attracts. It also attracts ants, yellow-jackets, raccoons, opossums and – if you’re in coyote, bear or cougar country – even more dangerous wild diners.

Make sure your garbage is secured in a solid container with a tight lid and remove anything rodents might use for shelter, such as wood piles. You can discourage voles, which like to “tunnel” in high grass, by keeping your lawn trimmed. Grass cut at two inches is tall enough to conserve some soil moisture but short enough to provide poor shelter for the vole species in California.

If you still see evidence of rodents, use traps to eliminate the existing rats and mice in or around your home. Traps pose little danger to humans and pets when placed in the small spaces rodents frequent. They are also effective, inexpensive and have no harmful side effects. There are also some environmentally friendly pest control companies that use exclusion and trapping methods rather than poison to keep your home free of rodents.

If you take these actions, still have a rodent problem and feel you must use some kind of poison, please use rodenticide products that DO NOT contain the active ingredients brodifacoum, bromadiolone, difethialone or difenacoum. These are the second-generation anticoagulant rodenticides (SGARs) most likely to kill non-target animals.

DPR’s decision to restrict those four chemicals is based on decades of monitoring studies and mortality incidents. Every monitoring study done in the last 20 years has found widespread exposure of predators and scavengers with SGARs, most commonly brodifacoum.

“We have owls, hawks, foxes and bobcats dying every year from these materials,” McMillin said. “Three endangered San Joaquin kit foxes died last year because they were exposed to SGARs, and those are just the ones we know of. Since animals usually go somewhere like a den to die alone, these are most likely just the tip of the iceberg.”

CDFW’s Wildlife Investigations Laboratory confirms that these deaths were caused by SGARs but the department can take no further action as long as the products’ use by consumers is legal. Typically these animals are found severely weakened and are taken to wildlife rehabilitators, where they are often bleeding and bruised, and die shortly after.

The EPA has been working with rodenticide manufacturers to develop safer rodent control products that are effective, affordable and widely available. Nearly 30 companies that produce or market mouse and rat poison products in the U.S. have adopted the recommended safety standards, including Tomcat products by Bell Laboratories, Assault brand by PM Resources and Chemisco’s rodenticides.

To learn where you can safely, legally dispose of rodenticides containing the four most dangerous anticoagulants in your area, see the Department of Toxic Substances Control web page on household hazardous waste at www.dtsc.ca.gov/HazardousWaste/UniversalWaste/HHW.cfm.

You can learn more about rodenticides and wildlife on CDFW’s website, at www.dfg.ca.gov/education/rodenticide/.

To learn how to use nature to deal with pests, avoiding toxic chemicals, visit the University of California, Davis webpage on integrated pest management at www.ipm.ucdavis.edu/PMG/menu.homegarden.html.

The EPA’s webpage on Safer Rodenticide Products is also an excellent source of information, at www.epa.gov/pesticides/mice-and-rats/.

Media Contacts:
Stella McMillin, CDFW Wildlife Investigations Lab, (916) 358-2954
Dana Michaels, CDFW Communications, (916) 322-2420