20 mule team borax works on all insects! It is actually an enzyme that boosts the cleaning power of laundry soap, but also increases the metabolism of insects so that they "burn out". It works for fleas, spiders, ants and all kinds of other bugs, but doesn't do anything to warm blooded creatures. It is also very cheap and easy to find, and is not "poison" to us or animals! The insects take it back to the nest, die, get eaten, then it works on the others in the nest. Enzymes are great cuz they keep working!
Neem oil also works, but is expensive and stinks really bad. I use it for ticks and fleas on my dogs, also for mange, both sarcoptic and demodectic (neighbor's dog, not mine!)Both are organic, and work well. No documented incidences of resistance. No known side effects, except for the nasty smell. I think it might work on mites..........have to look it up for chickens.