Just a little solid info here on mites folks....(thanks to VPI but the bolding is my addition)...

The protonymph stage lasts from three days to two weeks. This stage is mobile and may move considerable distances. Protonymphs are able to detect and are attracted by the smell of snakes. They require a blood meal to metamorphose to the next stage. Unfed protonymphs are pale ivory or yellowish in color, and they are almost invisible to the naked eye. The sharp-eyed, observant keeper may notice pale protonymphs walking across scale surfaces, especially on a snake's head plates. When engorged after a blood meal, protonymphs are dark red, smaller than adult females and not black in color. After full engorgement, protonymphs become active. Typically, they leave their host snakes and travel until they find a dark, humid location in the snake cage, where they shed, 12 to 24 hours after feeding.
It is common to find engorged protonymphs drowned in the water bowls in snake cages, often the first obvious sign of the presence of snake mites in the cage. The observant keeper will notice them sunk to the bottom of the bowl, looking like little flat pieces of pepper that, upon close inspection, are seen to have legs.

Since obviously this is the stage in the life cycle of a mite that it is most "visible" and seen easily by the naked eye, then how do you explain not seeing something that can be around for "3 days to 2 weeks" on a snake you are shipping out to customer or in that snake's enclosure or in an enclosure in that rack. It seems Ed has found and now treated these mites so how in the world did Shelby end up with two snakes with visible mites. They were invisible and now suddenly visible?????