Any infestation of lice or mites should be treated, along with the coop, nests, and roosts. The bedding has to be removed, spray the coop, replace beeding with fresh. Permethrin 10% spray is ver good for treating the chickens and coop, but the dust may be better for the chickens during cold weather.
It is important to find out if you are seeing lice or mites. Mites need treating at least 3 times, 5 days apart to get the mites, then the hatched eggs. Lice need treating at 10 day intervals to get the live lice, and the newly hatched eggs. Here is a good link to read with pictures:
http://www.the-chicken-chick.com/2012/08/poultry-lice-and-mites-identification/
It is important to find out if you are seeing lice or mites. Mites need treating at least 3 times, 5 days apart to get the mites, then the hatched eggs. Lice need treating at 10 day intervals to get the live lice, and the newly hatched eggs. Here is a good link to read with pictures:
http://www.the-chicken-chick.com/2012/08/poultry-lice-and-mites-identification/