Dance flies, family Empididae, got their name from the habit of bobbing up and down in the air as they fly in swarms. They mate on the wing, and perform the same dance.
The dance flies in 1, 2 and 3, Empis sp., were mating on a native rose near the mouth of the Elwha river in Washington. Other pairs were flying nearby. Males of some dance fly species offer a nuptial meal to a female. That’s the third fly visible in 1 and 2.
Image 6 shows the typical complex and conspicuous male genetalia.