Identifying Bat Activity in Your Attic

Yes, all nine species of bats native to Michigan are legally protected by the Department of Natural Resources (DNR). It is illegal to harm, trap, or kill them at any time of the year. Because of this, bat removal is highly regulated, particularly during the maternity season. From late May through early August, female bats raise flightless pups in their roosts. Performing an exclusion during this blackout period traps the babies inside, leading to inhumane deaths and severe odor issues inside the home. The only legal and safe time for live exclusion is in the late summer, early fall, or spring before the pups are born.

Absolutely not. First and foremost, there are no legally registered poisons or baits for bats, and attempting to poison them is a strict violation of the law. Second, over-the-counter gimmicks like ultrasonic sound emitters, strobe lights, peppermint oil, and mothballs are completely ineffective. They will not drive an established colony out of a warm, safe attic. The only proven, permanent, and legal method for bat removal is professional live exclusion—installing one-way doors that allow the bats to fly out to feed, but prevent them from re-entering.

Bats only need a gap the size of a dime (about 3/8 of an inch) to slip into a house. They typically find entry points high up on a structure, taking advantage of gaps behind fascia boards, ridge vents, gable vents, or failing chimney flashing. To keep them out permanently, the home must be meticulously sealed. However, amateur repairs often rely on standard spray foam, which looks aesthetically poor, breaks down in UV light, and is easily compromised by other wildlife. A true, professional-grade exclusion requires commercial materials like 1/8" hardware cloth, proper black roof sealant, or specialized wildlife-repellent foam that actually holds up to the elements over time.

Many homeowners hope the problem will solve itself when the weather turns cold, but that is a costly misconception. While some bat species migrate, the Big Brown Bat—one of the most common attic-dwellers throughout Oakland, Livingston, Genesee, and Lapeer counties—will often hibernate right inside your attic or wall cavities. They seek out micro-climates in your home where temperatures stay just above freezing. If a proper exclusion isn't performed, the colony will simply wake up in the spring and continue multiplying.

Yes, bat guano is a significant health hazard and should always be properly addressed. As guano piles up under a roost, it ruins insulation, damages drywall, and creates an overpowering ammonia odor. More importantly, in enclosed, poorly ventilated spaces like an attic, drying guano can harbor the fungus responsible for Histoplasmosis. This is a severe respiratory infection that humans can contract simply by inhaling the airborne spores. Once the bats are entirely excluded, the contaminated insulation needs to be safely removed, and the entire space must be sanitized and deodorized using proper respiratory protection.