Funny you should mention it. Recently while reading a magazine at the bookstore, I came across a blurp about flies not liking Vanilla. The gist is that they hung vanilla scented car airfresheners where ever it was to keep the flies away. You might try this. As for mites etc. etc. and flea collars I can't say, but you might want to try to find out why you have a fly/crawly bug problem to begin with. I keep a rake near the coop so I can stir up the chips under the roost. You can also toss some scratch in so the chickens keep things mixed up as well. While cleaning my hoop coop, things were pretty dusty and dry, but the corners where wet. They got extra DE. Nothing beats a good cleaning. Flies and crawly bugs breed where it is dark and wet/moist. This is why I suggested using DE to dust in dark corners and places larvae can live. DE works by drying up larvae. BTW, DE can also be used in basements as well. FYI, never, never cover ventilation sites in basements. I saw a house that had boarded up the windows. Not a good thing.