The Poop on Bat Poop
We live in Ashland and have bats in the eaves of our house. Will they damage the house? Should I do something about them? They poop on our deck... I've heard bat feces may be dangerous? How common is it to actually get sick from it?
Bats in the eaves of the house shouldn't cause any structural damage to your house. However, if they are accessing the interior of the structure, buildup of feces and urine (guano) over time can become damaging. Outside, on your deck for instance, it's unlikely that you would have sufficient quantity of guano to result in disease organisms in any significant number. Histoplasmosis does grow in the nutrient rich guano, but if you regularly clean the deck you probably aren't going to have much problem.
Bat Conservation International (http://www.batcon.org/) has good information on bats generally, including on managing bats in and around homes.