I rarely get time to post in the regular sections these days, but saw something in another thread that sparked me to remember an incident with mites....
Several years ago wild birds brought in red poultry mites that of course got onto my chickens and yowsa did I have a problem. Because my chickens roam around the pastures and inside the barns they spread like wildfire.
My hay was in a place where birds or chickens couldn't get to, but they spread every where else and if I picked up a bird I got them on me. Plus I could see them in the board cracks in several places around the barn.
I did several things to get rid of them...
For my chickens (if you have chickens) I dabbed them under the wing with a q-tip dipped in the injectable form of ivermectin. Since it is oily as well as absorbable, it got rid of the mites on the birds right away, then killed any new hatched mites that climbed on.
For the premisis I dusted liberally with DE.
Diatomaceous Earth (DE) if you are unfamiliar with it, is gaining in popularity as a natural alternative to chemical dewormers and parasite control for premises.
Google it and you will find hoards of info. Because it is safe to feed to animals (only short term IMO as it is hard on the digestive tract) you might be able to sprinkle it around the hay and kill the mites.
The nature of DE is to shred the exoskeleton of bugs, worms, and parasites, so no matter what type of "bug" that may be in your hay or hay area, it should help without harsh chemicals getting into the hay.