The fly certainly has a lowly station in life. However, the robber fly has adapted into a predator. Robber flies have turned the tables and feed on many flying insects like butterflies, moths, grasshoppers and beetles. Robber flies even attack other predatory bugs like dragonflies, ichneumon wasps, and even some spiders. They are sometimes called fly hawks because they swoop down on deer flies and horse flies in open meadows. The bearded robber fly is also known as a bee killer because, well, the name explains itself