Questions
How are the bats getting in my house?
Will bats cause damage to my house?
How can I tell if the droppings I find are from bats or mice?
Can I get rid of bats in my attic with light? With noise? With garlic? With moth balls?
How can I kill the bats living in my attic?
How can I safely get rid of the bats in my attic?
If I put up a bat house, will the bats leave my attic?

Answers

How are the bats getting in my house?
California bats, for the most part, are quite small, and can squeeze through an opening 1" x 5/8". Attics and walls provide good roost sites and bats often can enter these areas where the sides of a house meet the roof or chimney. If an entry has been used for any length of time, it becomes stained and easier to identify. You can also find entries by watching in the evening for the bats to emerge.

Will bats cause damage to my house?
Unlike rodents, bats do not make nests nor can they gnaw, so they do not physically harm your home. If they roost in a home long enough, however, large amounts of guano or urine can build up. This can be a nuisance and, in the eastern U.S. where histoplasmosis is commonly found in bird and mammal droppings, a health hazard.

How can I tell if the droppings I find are from bats or mice?
Even though they appear to be similar, bats and mice have very different diets and therefore their droppings are different. Mice eat a lot of vegetable material and their droppings of plant matter don't crumble. Bats eat insects and their droppings contain tiny bits of insect coverings (elytra). Therefore bat droppings are sparkly in the sunshine and crumbly in texture.

Can I get rid of bats in my attic with light? With noise? With garlic? With moth balls?
Unfortunately the answers are "no", "no", "no" and "no". Bats living in attics are usually maternity colonies. The moms may put up with just about anything to keep a good roost and protect their babies, including noise, light and strong smells. Bats are actually able to put up with smells so strong that humans must wear protective masks. And one of these "cures", the moth balls, have been found to be a carcinogen and dangerous to the people living in the house.

How can I kill the bats living in my attic?
Bats are mammals like we are, and any poison used on them can affect the occupants of the house. Additionally, bats are so important for controlling insects that it would be a shame to kill off this natural form of pest control. Rather than killing the bats living in your attic, you would be better off to get rid of them by excluding them. It is a permanent solution and you won't have bat bodies rotting in your rafters.

How can I safely get rid of the bats in my attic?
The best way to get rid of bats is also the safest - for both the bats and the humans involved. This is to exclude them. But in this area, this must not be done during May, June or July because these months are when babies are born and still unable to fly. Bats that live with us must still go out each night to hunt. If they can't get back into your house in the morning, they will have to go somewhere else to live. It is important to call an expert that knows how to remove and exclude bats from homes.

If I put up a bat house, will the bats leave my attic?
Unfortunately, no! Bats are extremely faithful to a preferred roost and attics are usually much warmer, quieter, safer and larger than a bat house. If you don't exclude them from the attic, they will continue to live there and probably not use the bat house. But putting up a bat house when an exclusion is being done is wise. When the bats are left homeless, they will have a new place to go and you will keep them in the neighborhood eating your bugs!