Moving fast doesn't sound like a mite.
You might try this. Take a white, wet paper towel. Hold your snakes with the towel and let them crawl through it. Wraping it around them as they crawl.
If you have mites you'll see small black moving dots. Try to smash and smear them on the paper towel. Mites leave a blood stain. Red to almost black in color.
Check the water dish for dead mites.
Have your snakes been soaking much?
The best product I've ever seen is Provent-A-Mite.
Pro-Products | Provent-a-Mite