The liquid is best to spray down coops and cracks and roosting bars, keep the chickens out until it dries (about 30 mins) mites generally come out at night to eat, so you may not see any on the birds at you would the lice. Also, if there are eggs on the base of the feathers, under beak and below ears etc....I generally just pluck those--as the dust won't necessarily kill the eggs, this is why retreatment in 7 days is important, it's the life cycle of the eggs.

