I would have to say they are mites. They have a mite spray that is called Black Knight that is used for reptiles. The stuff is so safe you can actually spary it directly on your reptile. So that leads me to belive it is more than safe enough for rats/mice. I was told about this from a guy who got his from Pro Exotics but several other places carry it also. I believe it is like $15.00 or so and will do its job. I say get a mite killer of some sort. Sterilize all your cages, treat the rats themselves, and the general area, and your problem should be pretty much eradicated........