Kaitlin and Ray have both demonstrated that even the smaller of the two mites hitching a ride on our fly can be identified to family from a not so great photo: heteromorphic deutonymphs (aka hypopi) of a member of the Histiostomatidae. They also correctly placed the larger mite to order: Mesostigmata. Not much luck on the fly, though, so I guess that means mites are easier to identify than flies? Anyone who has struggled with the generic key for this family in Nearctic Diptera might very well say yes. However, the family of the fly should be an easy guess for a dipterist.
Here’s a light microscope view (this is a Photon Challenge) of the venter of one of the histiostomatid hypopodes (yet another name for these deutonymphs) and a closeup of one of the pretarsal claws. The ventral shot is layered from three images in the wonderful CombineZP and the claw from two shots. The host association and characters visible in this image should give the discerning astigmatologist a good guess at the genus (I have checked with the North American authority on this one and he had no problem).
I’ll give one more hint on the mesostigmatans too – they also are deutonymphs.