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Empis borealis emerges in the early spring, and is often found on flowers feeding on nectar. This species shows sex-role reversal; the females, with their distinctive darkened wings, form swarms to attract males. Males capture a variety of insect prey before entering the swarm and choosing a mate. The mating behavior has been the object of several detailed studies (e.g Svensson and Petersson 1987-2000).