Blaste sp. (Barklouse (nonspec.) ) ♂.
Size: approx. 8 mm. Photo: 09/15/11, 9 pm.

This fascinating insect is a common barklouse. An expert (Prof. Mockford) identified it as Blaste sp. The genus has 12 species in North America. Barklice feed on fungi, algae, dead plant tissues etc. and are hence harmless, perhaps even beneficial to the trees they infest.  

bug guide (these photos):