DE won't work to prevent or kill and infestation.Thank you! I have been using diatomaceous earth in the henhouse but possibly not enough. I’ll ramp it up. and try to examine them.
Regularly check them over real well for mites and/or lice.
Google images of lice/mites and their eggs before the inspection so you'll know what you're looking for.
Part the feathers right down to the skin around vent, head/neck and under wings.
Best done well after dark with a strong flashlight/headlight, easier to 'catch' bird and also to check for the mites that live in structure and only come out at night to feed off roosting birds.
Wipe a white paper towel along the underside of roost to look for red smears(smashed well fed mites).
Good post about mite ID by Lady McCamley:
https://www.backyardchickens.com/threads/my-chicken-has-mites-now-what.1273674/page-2#post-20483008
Molting happens when the days grow shorter in their second fall/winter.Forgot to mention that they didn’t molt during our hot and steamy Gulf Coast summer. That surprised me.