What is your preferred treatment?At night with a good strong headlamp sneak into the coop and look for little crawling nasties along the roosts, nest boxes, and in crevices. They pop if you squish them and will sometimes leave little red smears if they have been feeding off your chickens. They are awfully common, as they can come from wild birds, they tend to live in the coop not fully on the chickens, and come out at night to feed. Think the chicken version of bedbugs. Occasionally they may hang out on a chicken during the day, usually around the face I have found, and when I see a lot of head shaking or scratching I know its time To check and treat for them again. My temporary coop/trailer arrangement has a problem with them, but the layer tractors don’t.
We have been battling them the last few years.