We have 22 hens and 2 roosters. About half the hens have significant bare spots above their tails. A few have them underneath on their bellies as well. This has been going on a for several months now, with the numbers of affected hens growing gradually. I have been reading and worrying about mites/lice, but had originally assumed it was the roosters trying to mate. Any ideas? If it is mites, would it not affect the entire flock after several months? Egg laying is good, though the numbers are down from early fall. We were getting more than 20 each day and are now down to about 15-18 a day. Any ideas would be really welcome -- I hate the thought of using chemicals!!