They’re congregating again; holding their conventions. Swapping stories, gossip, smells, locations of succulent trees, who knows what?
Box elder bugs.
They gather this way winter through spring: large masses of the striking red and black insects. They’re true bugs along with cicadas, leafhoppers, spittlebugs and aphids in the order Hemiptera: from the Greek hemi (half) and pteron (wing). This refers to the forewings of many hemipterans which are hardened near the base, but membranous at the ends.
Why box elder bugs gather is something of a mystery to me. Often it's on the side of a building where there is no food. They seem to be just hanging out.
The red and black hemis feed on the softer plant tissues: leaves, flowers and new twigs of female box elder trees, shunning the male trees (another mystery to me). They also dine on other types of maples and ashes but cause little damage to the trees.
One source noted that after the gatherings, the mated pairs leave the groups to mate. The females then disperse to lay their eggs in the trees, so perhaps these clusterings are like social mixers where unattached males and females can meet and get to know each other. (Pure speculation. If there's an entomologist out there, I could use a little guidance.)
I took this photo near the Visitor Center at Ijams after a rain. It looks like a pomegranate exploded. It appears to be mostly immature nymphs (the solid red ones) in various stages of development. The few adults in the picture (there's one in the upper right hand corner) have blackish wings.
-Photo taken at Ijams Nature Center.