If they are red or brown, they're not snake mites. It is hard to tell color, though, on a dark snake. If they are snake mites, it's not life threatening, just really an annoyance, especially if you have other snakes. If they are snake mites you will just have to treat them. If you do have other snakes you'll have to treat all of them. The mites, Or other bugs if they are not mites, could have come from the mouse, especially if it's a live mouse from a pet store. Eating it won't hurt your snake though. If they are snake mites from the mouse, I'd consider getting feeders somewhere else.