We had flying squirrels and bats in our attic a few years ago. When it got very hot or very cold they would occasionally migrate through various cavities into the main house where the temperature was controlled. We had to buy a large net to grab them. Eventually we hired a crew that went around the roof edge sealing up any openings and installing a one-way exit ( a mesh tube about 6 inches long). At dusk we sat in my truck in the driveway and watched them all exit and their frustration at not being able to get back in (nowhere to land). They made such a mess in the attic that we had all of the insulation removed and replaced. Total cost was around $10k. Best to fix this problem early.