The main signs of a bat infestation are piles of rice grain-sized droppings and dark urine stains. Ammonia smells, scratching and squeaking at night, or bats around your yard are also common signs.

Bat poop—yes, bat poop—is far more fascinating than you might think. You probably don’t give it much thought (unless it’s in your attic), but believe it or not, bat droppings have shaped history, ...