One of the most unusual insects found in soybean during late July and August has been the robber fly. Adult robber flies are noted for their voracious attacks on other insects, including wasps and bees. This behavior has earned them the name "bee catchers." They are usually found in open and sunny areas ranging from soybean fields to pastures to city yards and woodland edges. They fly mainly during the hotter parts of the day. Often they wait in open sunlit areas where they can command a good view of passing insects and then fly out to catch their prey.
When an insect is captured, it is injected with saliva containing enzymes that rapidly immobilize the prey and liquefy its tissues. In a relatively short time the robber fly is able to suck out the contents.
Many species of robber flies resemble bees or wasps and are often confused with these stinging insects. The species of robber fly, Diogmites neoternatus, commonly found in Iowa during July and August is not a pest of soybean. Because it resembles a wasp, especially when it flies fast and low across the ground, it may be confused with this stinging insect. The species of robber fly found in soybean does not sting and the ones I captured never bit me.
This article originally appeared on page 168 of the IC-488(20) -- August 19, 2002 issue.