Late in the afternoon on 16 and again on 18 July 2010 in warm (80-90 F) sunny weather, we (docents at Midpeninsula Regional Open Space District) saw swarms of tiny critters on a dusty trail through grasslands (wild oats, Harding grass, etc.) at 2000' elevation. They looked nymph-like, and they were only around 1 mm long and in constant motion (difficult photography). To get an idea of the swarm and the way it almost made the ground seem alive, check out a short video at http://tinyurl.com/2ayz37p . I also noticed that nearby there are lots of the adult hemiptera shown in the following photo: http://tinyurl.com/2bwvefp . I wonder whether the little ones could be hatchlings of those.