These critters were surely unwelcome guests under the tail of a damselfly: http://www.inaturalist.org/observations/252708
It is fairly common for pond mites to hitch a ride to whatever water body the damselfly might choose to lay its's eggs.

I took this damselfly for further examination primarily because of it's severe infestation with aquatic mites (see my next observation). But I was intrigued by the scary "prey's eye" view of it's mouth. Too bad it couldn't devour some of the mites hitching a ride on its tail.