In the Nick of Time
Bat-to-human transmission of rabies is extremely rare but not entirely unheard of. If you spend a lot of time working in attics or exploring caves where bats hang out, consider being immunized against rabies.
Around the House
Bat and bird problems are considered infestations. As such, they aren't covered by most homeowner's insurance policies. If defects in construction or products allowed the animals to enter your home, you could be protected under a new home or existing home warranty. Check with your builder or the policy issuer.
For the most part, bats are a good thing. They eat bugs — many of them of the noxious or pest variety — and their feces, or guano, makes wonderful fertilizer. However, there aren't too many people who would want to share their living quarters with these little creatures. And there are some good reasons for not doing so.
It is possible to contract diseases from bats. Rabies, of course, is the best known, but is actually a rare concern with bats, as very few carry the disease and they typically won't bite unless they're royally pissed off. That said, cats and dogs do risk infection if they pick up diseased bats, so it's a good idea to keep their rabies vaccinations up to date.
Histoplasmosis, a fungal disease that can be transmitted by inhaling the dust from dried bat manure (bird manure can contain the pathogens, too), is more of a concern, especially for people with immune disorders.
Bats — or, better put, the large amount of urine and feces they produce — can also cause odor problems and can damage wood. And young bats can drive you batty (sorry for the pun) as they will squeak without stopping if the females are away from the nest.
Bats are also secondary pest transmitters. Most bat colonies harbor bat bugs, an insect that is so similar to bedbugs it takes an expert to distinguish between the two. Where large bat colonies exist and then are forced to leave, the bat bugs will often invade the house, looking for a blood meal from the human occupants.
There are approximately 900 bat species in the world, with about 40 of them found in the United States and Canada. Most prefer natural roosts like hollow trees and cracks in rocks, but some species, especially in urban areas, will make their homes in attics, the areas behind shutters, and even downspouts. Because bats are loyal to their birthplaces, they'll return to the same roosting site year after year. Since they can live more than 10 years, this can be a real problem if allowed to continue.
Like most other pests, the best long-term solution for dealing with bats is keeping them out of your home and in the wild where they belong. With bats, however, it's about the only solution. Chemicals only work when they can be applied in small areas where their fumes can accumulate. Even then, their effect is temporary at best. As the fumes weaken, the bats will come back.
Other remedies, such as scattering mothballs where bats roost or installing ultrasonic devices, have not proven to be effective. It can take up to 5 pounds of mothballs to create a strong enough odor to keep bats from returning to their roost, and you have to keep on refreshing your supply for the best success. Ultrasonic devices may actually attract them.