Just to add my two cents -- when I first came across mites, I was like, "Ah, no, those are just pieces from the aspen bedding." Check the water bowl for drowned mites, and if you can, actually pick up one of the black flecks on your finger tip and try to look at it pretty closely.

And as for your heating pad, if you do not have a thermostat plugged into your heating pad, it can definitely get hot enough to burn your snake. A layer of substrate doesn't help, because your snake will move it around.