Recently we have received reports of swarms of hover flies (aka syrphid flies) around Indiana and wanted to take the opportunity to tell you a bit about this curious insect (Figure 1). Adult hover flies can sometimes be mistaken for bees or wasps, because they look a lot like them! Some people refer to hover flies as “sweat flies” or “sweat bees,” but these insects are actually quite different from bees.
Hover flies belong to the Order Diptera, or the true flies. The most abundant group at this time of year belong to the genus Toxomerus, which feed on pollen (Figure 2) rather than other soft-bodied insects, like aphids. Hover flies are typically lighter in color, have a characteristic abdomen-bobbing behavior, and cannot sting at all – in fact, they are harmless. Sweat bees, on the other hand, are typically dark or metallic in color, smaller than common bees and do have stingers. Both hover flies and sweat bees can be a minor nuisance. They are attracted to us by moisture and salts they get by lapping up our sweat.
In corn fields and other flowering crops, you will likely find the larval form of this insect (Figure 3), a small, rather plain-looking maggot, feeding in leaf axils and other areas where pollen collects. Be advised that the larvae are not pests, as they do not damage the crop. Rather, they are taking advantage of an abundance of pollen. This holds true for other flowering crops as well. As corn continues to mature at a more staggered rate than usual this year (a result of the wet spring and delayed/sporadic planting), you may continue to see these insects. Just remember they are not pests and cannot sting you, they just might be a bit bothersome hovering around you in large numbers!
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- Figure 1: Adult syrphid (hover) flies congregating on this gentleman’s cap. Photo courtesy of John Obermeyer, Purdue Extension.
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- Figure 2: Syrphid flies on sweet corn tassel. Photo courtesy of John Obermeyer, Purdue Extension
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- Figure 3: Syrphid fly larvae (highlighted in yellow) and detached corn anthers. Photo courtesy of John Obermeyer, Purdue Extension.
Larry Bledsoe, Laura Ingwell, Christian Krupke, Elizabeth Long, John Obermeyer,
& Cliff Sadof