Sounds like lice. You cant see mites, only scabs from them. But lice are little redish brown bugs that you can see. Dont worry, they are species specific. They probably came on the rats from the pet store.. It causes excessive itching. I would freeze food and bedding(if you use bedding) for atleast 48 hrs. (Always do this when buying new food and bedding as a prevention so you dont get reinfected wiith lice or mites)Vets sell topical kitten revolution and ivermectin. That will take care of the lice.I think you can also purchase ivermectin online. Depends on how old your rats are as to what is safest to use.If they are really young not sure what is safest to use. After you treat them, clean cage very thoroughly. Hope this helps.