The Trombidiformes is ahuge and diverse assemblage of mites, characterized more by the lack ofcharacters found in the other major group of acariform mites(Sarcoptiformes) than by many synapomorphies of their own (Lindquist 1996). Itincludes some medically important mites (chiggers, scrub itch mites) andmany agriculturally important ones. Among the latter are spider mites(Tetranychidae) and gall mites (Eriophyidae). With the exclusion of theSphaerolichida, the Trombidiformes is also known as the Prostigmata becausethe openings to the tracheal system are towards the dorsal prosoma of themite.