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Long-tailed Dance Fly - Rhamphomyia longicauda - female

Long-tailed Dance Fly - Rhamphomyia longicauda - Female
near Ailsa Craig, Ontario, Canada
June 25, 2004
Similar photos taken in 2003 were IDed as Rhamphomyia longicauda (Empididae) by Dr. Jeff Cumming in Ottawa, so I assume this is the same species. They're common in May & June in wooded areas near water. Females congregate in a swarm, and inflate abdominal air sacs (not visible here) in an attempt to fool males into thinking the swollen abdomens are full of ripe eggs. The hairy legs supposedly accentuate abdominal size. More info and a photo of the bizarre air sacs is in a PDF doc (186kb) here.

Update 14 March 2006: image moved from genus page to species page, based on IDed images here.

Another reference on mating in this species

Looks like this species has a really interesting mating system, where females swarm and males come in to select the most attractive female--the reverse of the usual system in flies, birds, etc.

Patrick Coin
Durham, North Carolina

I referenced that PDF doc under the image of a male here. It's the most bizarre insect story I've read: to male Rhamphomyia longicauda, the most attractive female is the one with the fattest abdomen and hairiest legs (slightly different than the situation in Homo sapiens).