Dr. Lloyd Glenn Ingles (c) California Academy of Sciences

What is a raccoon doing in my yard?

The omnivorous, nocturnal, and nimble raccoon is either prowling for its preferred or staple foods or on the hunt for a den site. In addition to pet food and garbage, raccoons will eat plants (fruits, nuts, and vegetables) and animals (grubs, crickets, grasshoppers, frogs, worms, fish, turtles, squirrels, rabbits, rats, mice, bird eggs and nestlings, among others). They're particularly fond of sweet corn and watermelons. In nature, raccoons will den in tree cavities, brush piles, or ground burrows. In our yards, these resourceful and often destructive critters will seek shelter in or under any structure they can enter. That includes attics, chimneys, crawl spaces, and wood stacks as well as the areas beneath porches, decks, and sheds.

Raccoons typically bear litters of roughly three to six young in April or May. These young will stay with their mothers for about a year. In urban and suburban areas, densities of well-adapted raccoons can reach 100 per square mile.

Benefits and conflicts

Raccoons will provide a little help with insect and rodent control, but they can quickly become pests themselves. Besides knocking over garbage cans, raiding vegetable gardens, stealing tree fruit, and rolling up freshly laid sod in search of grubs, they can establish dens in chimneys and rip off shingles or fascia boards to enter attics. They may also carry fleas, ticks, roundworms, rabies, and canine and feline parvovirus, among other potential health threats to humans and pets.

Strategies for coexistence and control

Habitat modification: If possible, remove woodpiles and trim overgrown shrubbery to reduce cover. Also, be sure to secure your garbage cans and lids and to bring pet food and water in overnight.

Fencing: Raccoons can readily scale fences and even open simple gates. A good way to keep them from clambering over or digging under your fence is to install a single electrified wire 8 inches from the fence and 8 inches above the ground. (If you don't have a fence, two parallel wires-mounted about 6 and 12 inches above the ground on insulated stakes-should also work.)

A commercial sheet-metal chimney cap or heavy metal screen (installed only if you're certain no young will be trapped inside) offers good protection against raccoons in your attic. Trimming tree branches back 3-5 feet from the roof helps, too-as long as you don't have other landscape structures they can clamber up instead. To exclude raccoons from open spaces beneath structures, install 1/4 or 1/3-inch galvanized hardware mesh, burying the bottom edge at least 6 inches deep and extending it outward, beneath the soil, about 12 inches.

Frightening devices and repellents: No chemical repellents have been proven effective against raccoons and no frightening devices will work for very long.

Trapping: Raccoons are relatively easily trapped but undesirable to relocate. A professional wildlife control operator is best qualified to remove them for you.

For more information

Prevention and Control of Wildlife Damage: Raccoons, University of Nebraska-Lincoln Cooperative Extension Division, http://www.ces.ncsu.edu/nreos/wild/pdf/wildlife/RACCOONS.PDF.

How to Manage Pests in Landscapes and Gardens: Raccoons, University of California Statewide Integrated Pest Management Program, www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74116.html.

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