Bats Inside Home

Problem: Bats become problem around or inside the home.

Background: Bats are the only true flying mammals that also have fur, jaws with teeth, and bear live young. Normally they do not attack humans or fly into their hair. Bats can carry rabies, though few fatalities have occurred due to bites from rabid bats. Another disease problem, histoplasmosis, is associated with some bat colonies. It is caused by inhaling spores or fragments of the naturally occurring soil fungus Histoplasma capsulatum. The fungus is most often found in soil enriched by excretions from bats and birds, such as pigeons and starlings. Some infections produce flulike symptoms, though many produce no symptoms or distress.

What to do: Some bat species congregate in colonies. In a building or a home the accumulated odors, droppings, mites, and lice may cause problems. Though persistent, bats have little capacity to chew or scratch through modern building materials. Excluding bats by locating and blocking all entry or exit points is the most cost-effective method of control. Bats enter buildings through various locations, including unprotected vents, broken windows, split siding, chimneys, or other openings. The smallest bats can crawl through openings ¾-inch wide (or through holes the size of a dime). Locate openings by brightly lighting the inside of potential rest areas at night and observing them from the outside. If this is not possible, observe from the inside on a bright day. Block larger openings with sheet metal or ¼-inch hard ware cloth. Plug narrow cracks with steel wool, oakum, or other packing or insulating material, then seal with an exterior caulk.

Special advice: Be sure all bats are out of the area being bat-proofed be fore the work is completed. Usually the entire colony will depart from the roosts within 20 or 30 minutes once the first exits, but this may not happen if the bats have been disturbed or harassed. Leave 1 or more well-used exits temporarily open; close after a few days after all bats have departed for the evening. Watch the building at dusk for several days to see if some openings were overlooked.

Helpful hint: There are no effective poison baits for bats because they primarily feed on flying insects. Chemicals may be used to kill bats where all other alternatives fail, though it is expensive and will not provide long-term control.