Orussidae: Guiglia schauinslandi - Parasitic Wood Wasp

A large number of wasps vigorously running up and down an inclined tree, chasing one another, occasionally in "trains" of 3 to 5 wasps, head to tail, and in masses, piled atop and around each other. I observed a few in which the chasing wasp would vigorously "nudge" the abdomen of the one in front.