Easy Bat De-Bugging

Ever since American pioneers cleared aboriginal forests to make way for today's agricultural landscape, many of the little brown and big brown bats that once thrived in hollow trees have moved their homes into old churches, barns, outbuildings and people's attics. Bats enter homes because well-protected attics become very hot in summer and act as an incubator for young bat pups. Because house bats have only one or two pups each year, protection of maternity colonies is important for their survival, says Margaret Brittingham, Penn State associate professor of wildlife conservation.

Bats are the original two-home species. Between late spring and mid-autumn, bats occupy their summer vacation digs in hollow trees, barns and attics. There, they create seasonal maternity colonies where female bats gather to raise their pups. If you find large accumulations of dry, black bat droppings the size of rice grains in (or in close proximity to ) your attic, you probably house a summer colony.

Come October, about the time of hard frosts, bats leave their summer colonies to seek winter refuge in caves where they hibernate through April. That makes late fall and early spring an excellent time to bat-proof your attic.

"By sealing holes in your attic from October to April, you can prevent bats from re-entering your house in the spring," says Gary San Julian, Penn State professor of wildlife resources. By acting within this time frame, you don't have to worry about unintentionally trapping nursing maternal colonies inside your home since destroying even a single maternity colony can have a long-term impact on local bat and insect populations.

First look for places where bats enter homes, suggests Brittingham. Bats enter attics through loosely-screened vents, roof peaks and where flashing has pulled away around dormers, roofing or siding. "Bats can crawl through holes the size of a quarter,' she says. To cover louvered vents or large gaps and cracks, use window screening or hardware cloth. Fill smaller cracks with expanding foam insulation or caulking compound.

Unfortunately, simply protecting your home from flighty residents could leave you with a significantly higher population of hungry mosquitoes. But you can ban bats from your attic while keeping their voracious appetite at work eating mosquitoes and other pesky insects in the neighborhood.

After sealing your attic, providing a bat box near your house as an alternative roost. "Bats are very site-faithful," said Brittingham, explaining that they habitually return to the same nesting site. With a bat box, the maternal colony has a safe place to raise its pups, the homeowner gets bats out of the belfry and your family retains the benefits of bat insect control.

The small bat boxes available at garden centers attract single males, but don't serve maternity colonies. To house maternity colonies, homeowners should build their own bat boxes capable of holding 100 to 300 bats. The interior should be divided into multiple roosting crevices, designed for proper incubation temperatures. Siting also is important, emphasized Brittingham. "The most successful bat boxes get at least seven hours of sunlight each day."