I use De when I clean the coop. I put down a thick layer of hay and new hay in the nests, I take a sifter and sift it over the hay really good and rub the roosts down as thick as I can get it on them, So far I have had no problem with flys,But ----------we do have ticks,and since DE is harmful to bees,I do not spread it around anywhere outside the coop. Since the hay from the coop is full of poop,it makes good mulch for my garden, and I don't think it should bother the bees. I do hang fly strips from the co op outside just in case any flys come visiting. Also check out Dawn419, she is one of the mods and also sell DE, so she can help you with anything you need to know about it. marrie