Our house has a porch on its north face. It is a lovely place to sit and enjoy the wildlife. There are a number of trees and a little flower garden/patio area. My wife has planted hostas at the edge of the porch.
Last weekend I noticed a huge number of insects flying just above the hostas.
Closer inspection showed that the insects were cuckoo wasps.
Cuckoo wasps are known to be nest parasites of other hymenoptera–bees and wasps. They leave eggs in the nests and the larva feed on the young of their hosts or on the provisions provided for the young. When they feed only on the provisions they are called “cleptoparasites”.
Occasionally they would all clump up together–presumably mating and/or competing for the opportunity to mate.
Why are there so many of them? I am not sure, but I think they might have something to do with the digger bees that live under my porch.