I have only a couple chickens, out of 20 adults, who seem to have some very tiny white bugs on their faces. Maybe other places, but only noticed on the face. They seem to dart in and out of the feathers on the face, around the eye. None of the others show any signs. We have DE in coop and sprinkled on the roosts. What am I likely dealing with here, and how can I rid them from my flock?