Semaphore flies 

What a great name for these male flies with the semaphore-like courtship ritual. A little easier than their scientific name Poecilobothrus nobilitatus! They did remind me of the semaphore flag signals as used by the navy when signalling from one ship to another. The males use their white-tipped wings to signal to a potential female to mate with him. Both male and female flies are actually predators on small crustaceans, enchytraeid worms and small insects, which they find in and around the pond and mud.

According to Lunau the courtship ritual of the males has several parts but is focused on one female who herself may be observing many other males also displaying to her. Males defend small territories about 100 sq cm in size against other males and court females who enter it.

Well written BBC Wildlife article here by entomologist Martin Drake.

If you see these flies on your pond your and send in details at this website Dolichopodidae Recording Scheme