redmonsterwithblueeyes's Identifications

At dusk on an expansive hillside lawn, hundreds/thousands of these beetles began to appear out of the grass and fly into the treetops where they buzzed around without settling. Eventually mating pairs could be discerned on some of the lower branches, but mostly it just looked like a lot of buzzing! Never seen anything like this before. It was a perfectly clear evening, about 70F, the solstice, and a full moon.