Have you ever watched bats flying around at night? It might be a little uncomfortable how close they sometimes swoop by your head, but the reason for this is that they are eating bugs that are attracted to your body heat. A single bat can eat as many as 8,000 mosquitoes in a single night, so their services are definitely welcome. They are, however, not welcome in your attic. Bats can spread disease since they will use the floor of your attic as a toilet, and of course, it can be very startling to have bats fluttering around your head when you step into the attic.
How can you keep them out? Since bats are nocturnal, they seek out a dark area to sleep during the day, so having the light on in your attic might discourage them. If that doesn’t help, you will need to find their entry points and plug them up. If the bats are already in the attic, installing something called a one-way excursion device will let them leave the attic but not come back in again.