I've had my female ball python since the middle of January (this year). She has never shown signs of mites and hasn't had contact with any other animals (other than food). For about three weeks now, she's been soaking a lot in her water dish. Sometimes it's her whole body; sometimes it's just her front (or back) half.

I'm using aspen bedding as substrate, and although I haven't found any mites in it, I think she might have them. She's soaking a lot (see above) and seems to be even more lethargic than when I got her. I've moved the bedding around to look for them and can't find any, and I can't see any on her. I've picked her up, hoping they'd move or get onto me so I could be sure they were there. Nothing. However, there are black spots in the bottom of her water dish. Usually two to five of them, no visible legs or anything, no movement, just sitting on the bottom of the dish. They're black and about the size of a pinhead.

EDITED: Upon closer inspection, I think I can make out a head. I squeezed one with a pair of forceps, and it has a rust-colored liquid inside. I'm treating this as mites and will be buying Provent A Mite tomorrow. My question is, how did she get mites in the first place? She's not been in contact with any animals other than her food, and this behavior didn't exist up until three weeks ago. She's eating just fine, and is due for a shed soon.