I have a house that is 104 years old . I do not get bats in the house all the time . They use to come in about once or twice a month then I did not get any in the house for years. Now I have has a bat in the house for the last to nights. I would like help in keeping the outside and not in my house. Can you please tell me just what I am looking for so that I will know it when I see the stain. And how many entries would they have?

All you need is one tiny opening into the house. A broken vent screen... a small hole... you just need to look.

A hole the size of a quarter is big enough. Put a bright light in the attic and look around the outside of the roofline at night.

I believe this may be baby season for the bats so be careful if you should find the hole the bat came in not to seal it so the mother bat is outside and the baby bat is inside. For phenomenal information on bats, go to www.batworld.org Bat rescue, bat rehabilitation bat conservation and sanctuary for bats. A non-profit organization dedicated to bats!
Their website has lots of correct information that you will find helpful and there may even be a bat rehabber in your area. Bats are dying by the thousands and are having a terrible time right now due to white nose syndrome so if you can keep from causing the death of one or two (like a mother and baby) that would be great! They do a tremendous amount of good for us (eating mosquitos and pollinating fruit trees and such) so it is important that we help take care of them. Thanks.