Ooh, I know exactly what you’re talking about, but I don’t know what they’re called either. Defintely not chiggers, they don’t bite and they just mind their own business. We used to have them on the brick steps of my parents’ house outside Boston.
Guess what? We’ve had an infestation of these at our office, and have identified them as clover mites:
http://ipmofalaska.homestead.com/files/clovermites.html