Not only do they make even the bravest of men fall to the ground and assume the fetal position, those nasty bats in the attic can also spread rabies and, worse, contaminate the air with their foul feces, the fumes of which can lead to deadly histoplasmosis. Then there are the snakes that go hunting after them for a good meal. So what are they all doing in your attic? They found a way in—through a hole or crack in your house's skin. If you find a gap even as small as a finger's width, just assume something awful has taken advantage of the easy access. Then deal with it.