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Robber Flies

August 29, 2001

Robber flies, family Asilidae, are common on flowering plants. These flies appear larger than they are due to their long legs. They are about 1 inch long and usually tan, with large, bulging eyes on a triangular face. Their wings are transparent.

These are predatory insects, frequently seen on or near blooming plants, where they fly out and capture bees, flies, and other visiting insects. They are not dangerous to people, but their large size and quick flights can be intimidating. It would be difficult to control them with insecticides because they are not feeding on the plant—they are using the flowers to at-tract prey for them. In addition, to avoid killing polli-nating insects, one should not spray blooming plants. Spraying the plants kills many more pollinators than the robber flies eat. If necessary, removing the blossoms would probably cause the robber flies to leave.

Robber fly larvae are beneficial. They live in the soil, where most species feed on white grub larvae and pupae. Some species' larvae feed on grasshopper eggs.

Author: Phil Nixon


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