DE is not that effective and takes a long time to work on a bug - if at all. I don't use powders of any sort around my chickens because of respiratory issues and DE has a lot of warning on the label to use goggles, mask, and gloves, so I decided not to use it - especially since it is not a guaranteed bug deterrent. If you want to keep your house chickens free of feather lice/mites I use organic enzyme Manna Pro Poultry Protector on their bodies and their housing (directions on label). Safe enough to use on 9-day-old chicks. I received a shipment of two pullets and they had feather-lice on them right out of the crate so I immediately used Poultry Protector on them and there was no lice almost immediately. Since Poultry Protector is safe to use as often as wished, I continued using it for a couple more days on the pullets just in case. A week later I followed up with another application to the pullets just in case any lice eggs hatched or I missed any. I use Poultry Protector once a month on our 4 hens and then use it on parts of their coop like nestbox and perch crevices as preventative maintenance. The stuff really works and I don't have to be afraid of poison or waiting around until maybe DE works or doesn't work.
http://www.the-chicken-chick.com/2012/05/diatomaceous-earth-de-benefitrisk.html
DE works, just not on the spot. It causes insects,,all insects, with ecoskeletons to be cut inside and out, the body fluids escape, and they die. Like you, if I see any bugs on any of my animals, I want something immediate. But I do use DE alot as prevention. You can dust birds directly if you wish, and I use it to worm birds and dogs. I do use face mask when I spread it and dust is in the air. Once it is where its going, however, I take mask off.