Thanks for that ID! I tried to feed the grubs to a siren (big two legged salamander) but it didn't like them. I'm guessing the mites are opportunists hitching a ride, maybe eating fungus and detritus... maybe eating smaller mites? They are pretty fast little mites. Good to be fast if you are catching things to eat. Just speculating . I blew some off the beetle into a small container with moist sub so I can see if anything goes on in there, throw a cricket leg in there or something and see if they feed on it.