Bats. Can't live with them; can't live without them.
We had bats in our attic. Beware, the guano can be deadly. I was lucky to still be breathing when I learned that. I was cutting some lathe and plaster with a sawsall from the ceiling to access an impossible space when a chunk dropped and I was showered in black dust and pellets. A petrified bat carcass bounced off my head as a bonus. Humidity + heat + guano = dang stanky. Can't kill them here. It's the law. So we set up a screen or one way door (
http://www.batmanagement.com/havebats/nuisance.html) so bats could get out but not back in. I also used a case of caulk to plus the gaps in the siding and then had to paint. And it was high. My house is four stories and we're talking dormers up top. Just a couple more reasons I say I'm lucky to be alive.