I use cat frontline, just a drop on the back of the neck to treat lice, though i rarely seem to get them. But this summer i've had dreadful problems with red mites, i normally use ppoultry shield to great effect but this year it's been useless. i think its because it works when the house is soaked for a few hours whereas this year the stuff was drying within 10 mins of being sprayed on. I've now discovered a wonderful product called diatom powder it works by dehydrating the insect and destroying its shell and they can't build up a resistance to it unlike chemicals. It works on all insects so would kill lice too and its safe for the chickens to eat as well. google it, i can't recommend it highly enough and believe me the mites nearly drove me to consider giving up the chickens.