Atomosia puella (Robber Fly).
Size: approx. 5 mm. Photo: 07/13/11, 10 am.

Robber fly on a pine tree. I believe the head-down position is somewhat characteristic. North America has close to 1,000 different species of robber flies (Asilidae) . They stab and inject other insects with saliva containing enzymes capable of paralyzing and digesting the insides of their victims. One expert on the bug guide suggested that this specimen is Atomosia puella. It has been reported that large robber fly species can kill humming birds 
bug guide (this photo):