patsy-
Thank-you for looking for an acceptable way of getting them out of your attic. I would ask you to wait a couple of months until they migrate - they will get rid of themselves. Bats are protected and highly beneficial. After they leave, you must seal all the entry/exit holes so they can't come back next summer. If you walk around your house just after dark you should be able to see them on their way out for dinner. There may be more than one entry point so look closely. If you want to know more about these wonderful mammals, go to
http://www.batcon.org/.
Tony M