Dance fly mating wheel - Empis sp.

This crazy tangle, I believe, is a dance fly mating wheel with a prey species too... Apparently this is typical mating behavior for many dance fly species - the male approaches a female swarm with a 'gift' to attract one of them. This particular species, it appears, still offers an edible gift - whereas other Empis species offer worthless items, like a silk balloon or a piece of dried leaf or twig.
Dance flies are related to robber flies.