Flies of the Family Asilidae are known as Robber Flies and are fierce predators.  These flies most often capture their prey in flight and do not hesitate to attack butterflies, dragonflies, grasshoppers, bees, nor wasps.  The genus Promachus is widespread across the United States, and species within this genus are very similar to the one pictured here, with an elongate body and with eyes that bulge out far above the head.  Members of the Genus Promachus are among the largest and fiercest of the Asilidae.