Syrphid flies, sweat bees and hornets

By John Fulton

[September 07, 2011]  Everyone seems to be having troubles with "sweat bees" these days. Or are they really sweat bees? Sweat bees are about a quarter of an inch long and are usually metallic green in color. The yellow and black insects that are commonly called sweat bees are actually flies -- syrphid flies to be correct.

Syrphid fly is a generic name given to an entire group of flies. There are some differences in appearance and color, but yellow and black is the major coloring in our area. Other names for syrphid flies are hover flies or flower flies. They tend to hover around your arms and face when you have been perspiring and then land to lap up the sweat. They are also commonly found on flowers -- hence the flower fly name -- and do a good job of pollinating.

Syrphid flies are actually beneficial insects. They help pollinate; their larvae feed on dead organic matter; and the larvae are predators of aphids. They cannot sting, but their mouthparts can usually be felt when they lap up sweat from sensitive areas. You may feel a slight pinch.

Yellowjackets are the other common yellow and black insect this time of year. Yellowjackets can be very aggressive in biting and stinging. They are usually about twice the size of the syrphid flies, and the easiest way to tell them apart (without getting stung) is to count the wings. Flies have one pair, and bees and wasps have two pairs.

Yellowjackets are most frequently encountered when they scavenge for food. Their habit of feeding on nectar and sugar can create a nuisance. Yellowjackets are attracted to open cups and cans of soda and other sweet liquids. Contact with the wasps can be decreased by reducing these attractions at picnics and other outings. They are also attracted to open cans of garbage, bright flowery clothing and floral-scented perfumes. To reduce yellowjacket problems, all outside garbage cans must be kept clean and well covered. In situations closer to home, eliminating overripe fruit from gardens and orchards will dramatically decrease the number of scavenging yellowjackets. Having gatherings indoors and using screens on windows will also help avoid yellowjacket problems.

There are a variety of traps on the market that claim to attract yellowjackets. These traps are baited with the scent of rotting fruit or other odors equally as appetizing to the yellowjackets. It is questionable whether these traps can out-compete the natural and man-made attractants described above. However, it is certain that through proper sanitation and removal of natural and man-made attractants, yellowjacket contact can be reduced. The traps can also attract more yellowjackets if placed close to the home or patio, so place them to attract the insects away from where you'll be. In situations where the potential for repeated contact exists, other management methods may be necessary.

As for the syrphid flies, no controls are going to be very effective. On the other hand, there really isn't much need for control. They are mainly a nuisance pest and very agile. They will probably be able to avoid that aerosol spray. Inside the home, a swatter and a vacuum cleaner are probably the best tools.

[By JOHN FULTON, University of Illinois Extension]