Macrochelid  mites attached to muscid. 
Mite predators of fly eggs and first-instar larvae are mainly species of the families Macrochelidae, Uropodidae and Parasitidae. As the manure accumulates and ages, these predatory mites exert some biological control. The macrochelid mites are better known and are frequently extremely abundant in livestock and poultry manure. They are brown, fast moving, attach to flies and are thereby transported to new areas.
Macrocheles muscaedomesticae mites attached to Stomoxys calcitrans. 
Macrocheles muscaedomesticae females can detect the odor of manure and flies. As manure dries, its attractiveness declines while visiting flies remain more or less constant in their attractiveness. Once the attractiveness of the manure is less than that of a visiting fly, the mite will grasp the fly and be carried off. Upon the fly visiting an area of fresh manure, the mite detaches due to the attractiveness of the fresh manure being greater than that of the fly. This is a case of phoresy, not parasitism.