where do mites come from?

[O'Mathghamhna]

While snake mites don't feed on mammals, if the shop where you purchase your mice has a mite infestation then it's possible to bring home a hitchhiker.

Or if someone tries to feed live and then takes the snake back, and the shop resells it... If the snake that initially refused it had mites they will hop on. :/ So frustrating!