I read more about bats at the Florida Bat Conservancy and it all makes sense - more bats = less insects:
Bats are the most important controller of night-flying insects, including many agricultural pests. One small bat can eat up to 3,000 insects in a night! Unfortunately, many bat species are disappearing at alarming rates. Disturbance or destruction of roost sites due to development and vandalism constitute the greatest threat to the world’s bats. Most bats living in Florida prefer to roost in mature trees, dead trees (snags), or in caves. However, many bats take up residence in buildings, or other manmade structures, due to loss of habitat. Bat houses provide alternative roost sites for Florida's colonial bat species. A bat house in your backyard will offer local bats a much needed place to live. They will also do you a return favor by helping to control the insects in the area.Who knew? Bats can help with insect control. In Florida (and certainly in my backyard) we have plenty of insects. Some of them are vicious little blood sucking beasts (that may be an exaggeration, but my wife tells me I have a flair for the dramatic sometimes). Maybe I should build a bat house. Lucky for me, the bat conservancy has plans available.