Semaphore flies, with a language all of their own

 There are scores of these colourful little semaphore flies in the garden at the moment, performing their highly entertaining courtship rituals, which involve a lot of wing-waving.

Poecilobothrus nobilitatus is small but exquisite, 7mm long, with emerald eyes that burn with inner crimson fire in the sun, a bronze body shot through with green and purple iridescence and, in males, white spots on the wing tips.

The male semaphore fly’s courtship dance follows a predictable pattern. He spots a female  and a brief aerial pursuit ensues, performed with such speed and agility that it is impossible to follow with the naked eye. She settles again and he lands in front of her, white wing tips whirling in a frantic effort to semaphore his intentions, often met with total indifference. Usually, she continues to feed, rarely turning to face him. I have watched these rituals many times, and have yet to witness a successful mating. 

Sometimes two males, like those in the picture above, will face one another and, apparently, attempt to intimidate each other by vibrating their wings - but who can tell exactly what these rituals mean? Only Poecilobothrus nobilitatus can really decode this semaphore signalling language.

Sometimes the flies adopt this head-down, tail-up posture but they rarely stay still for long.

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