Sunday, September 13, 2015

Green-eyed Robberfly

This fantastical creature flew up and landed on the path in front of Erika and me as we hiked in the Carleton College arboretum prairie. At first we thought it was a monster dragonfly, but the wings did not lie correctly for a dragonfly. Googling “green-eyed fly” quickly landed identification as a Robber Fly, one of the “largest and most abundant families of present day insects" (Robber Fly Website). Over 7000 species are known worldwide; I have previously blogged on Machimus notatus, another species of Robber Fly.

Further search on the Internet came up with Wisconsin Butterflies. These flies are not butterflies and do not always have green eyes, but Green-eyed Robber Fly seems an appropriate name. The Wisconsin site just calls it a Robber Fly, Promachus vertebratus. This species is the most common Promachus in Wisconsin and, with its spotted abdomen, is relatively easy to identify. The species inhabits disturbed areas and old farmsteads. They fly from mid-July into early September. Robber Flies feed on other insects, mostly those that eat plants. Some species of Robber Flies can decimate apiaries. Other insects such as parasitic wasps and flies are also eaten.

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