I think these usually swarm after the first heavy monsoon storms in July/August, except this year, there weren't any. So a nice unseasonal October rain seemed to finally trigger the swarming of this group. There were hundreds of winged females(?) emerging in the morning. I found only one small-headed male(?) but I didn't have time to watch until the swarm actually took to the air.
The green leaves on the ground are what they cut last night from a Texas Ranger bush about 20 m away.