Bats can be found in most parts of the world with the exception of extreme cold climate and severe desert. They are a very beneficial part of nature. Scientist consider bats one of natures own pest controls.
About 70% of the bat population consume insects as their main diet. The Virginia big-eared bat fore instance. will devour half its weight in bugs every night during warm weather months.
As beneficial as they can be for the natural remove of insects, having them inside of our homes is not a good thing. Bats can cause a lot of damage to your house when they try to make it their home also. These critters can spread a number of diseases.
Keeping bats out of your home is difficult thing to do because of their size and ability to cling to the side of a building. They will nest under siding shakes, in louvers, soffits, etc. Pretty much any where there is a small crevice for then to tuck themselves into.
Here is some great advice from WFmynews2 on keeping them out of your home.