It sounds like some kind of spider mites. There are many different kinds of mites. You could try Borax (sodium borate) which is poison to anything with an exoskeleton but about as harmless as salt to mammals. It works on ants but I'm not sure how well it will work on something as small as a mite. It has to get onto their shell to be effective and a mite could just walk around it. It's cheap and harmless so could be worth trying.