We normally see the northern paper wasps, Polistes fuscatus, come and go through a crack in our eaves but the sight above was very impressive. A tight scrum of wasps four deep were crawling all over each other, mostly males. None were flying around and there were more hanging around the edges as if thinking about joining in. You can watch the action on this Youtube video.
I suspected that it was a wasp orgy and sent it to an expert (on wasps, not orgy's), Chris Barnhart. He confirmed that it was a mating scrum and sent this link which described this behavior in Polistes gallicus. They write:
"At the end of summer, males of Polistes gallicus fly in swarms around vertical landmarks and land in clusters on their favorite perches, where they drag their legs and abdomen. Here males occasionally crowd around a perched female; they make no effort to defend an exclusive mating territory but instead attempt to copulate by displacing rivals from the female."
Another source from NC State adds more details.
"Paper wasps show types of swarming behavior during the cool and cold times of the year when there are no nests and no young larvae to protect. During the fall, this behavior is connected with mating and is the wasp version of "boy meets girl."
Male wasps look for the best place
to "hang out" and attract females. On these warm days during the fall,
the future queens become active and fly about. They go on to say that the females tend to seek high spots like towers or the highest house in a neighborhood (like ours on a bluff). Males seek out good spots and emit hormones (pheromones) to attract females. That is likely what all the bumping and grinding of abdomens is about in the video.
Ordinarily I spray for them when they are tending the nest as they become defensive and sting occasionally when we walk around. They will patrol the deck but don't usually sting seated guests unless someone instinctively swats at them. The books say that at this stage they aren't aggressive but I am not sure how many wasps read books.
Since these were six feet from our front door and within reach of anyone passing by, I sprayed them, then counted 42 bodies with more dropping through the gaps in the deck. While they are a part of nature and considered "beneficial," I don't think I upset the balance of nature too far and I am confident that they will be nesting here next year.
There is more on Polistes fuscatus in Wikipedia.