I waited until they went to roost, I spritzed their backs and then spritzed up underneath them into the butt fluff since the vent area is mite prone. I have thought to spray under wings too, but my birds really aren't big on being handled. The mites typically live off the birds then come onto the birds at night to feed. I also sprayed the roost at the same time, so hopefully somewhere in the mites' journey from their hiding spot to the chickens to feed while the chickens roost they will encounter the spray and drop dead. This is what I'm hoping anyway. It's been about a month and things are looking a million times better. I will probably spray things down again when I clean the coop this week to be safe, I will at least hit the nest boxes and the roost anyway.