Despite having a generally poor reputation, flies are a large and diverse order of insects that includes many beneficial species. Many flies are actually considered beneficial because of the pest control or pollination services they provide within farm fields and gardens. The hover flies (Order Diptera, Family Syrphidae) are one group of “good flies” found commonly in Ohio.
The hover flies are a diverse family, ranging widely in size, color and body shape (Figure 1). They are called hover flies because of their ability to hover in midair by vibrating their wings very rapidly. Hover flies generally mimic bees and wasps and therefore often cause panic when encountered, but they do not bite or sting. Many people will incorrectly refer to them as “sweat bees,” which do exist and can sting, but hover flies are harmless and fairly easy to distinguish with a bit of practice. Syrphidae are a particularly beneficial insect to have around because many serve as predators as larvae and pollinators as adults!
Identification
Hover flies range in size from ¼ to 1¼ inches and are typically patterned in yellow and black, but can also have red, orange or brown markings (Figure 1). Being true flies, hover flies possess only one pair of wings, whereas other flying insects possess two pairs of wings. That is one way to quickly determine whether you are looking at a fly or a bee, for example. In addition, hover flies lack the long antennae that most bees and wasps have. Hover flies also have very large eyes relative to their head size.
There are thousands of species of hover flies worldwide and many in the state of Ohio. Some are small and shiny, like the common genus Toxomerus (Figure 1A), while others are robust and hairy like the genus Merodon (Figure 1B), which is a mimic of the bumble bee. However, one thing all hover flies have in common is a spurious wing vein that is open on either end (Figure 2).
Behavior
Hover fly larvae occupy a variety of habitats. Most are predators of plant-sucking insects like aphids, scales or thrips and can be found on foliage (Figure 3). The pupae of predatory hover flies are usually found adhered to plants. Some species of hoverflies live in stagnant water or on decaying vegetation and feed on detritus. Those in the genus Eristalis are detritivores; they are referred to as rat-tailed maggots as larvae (Figure 3B) and drone flies as adults (Figure 1C). The “tails” are actually long siphons used for breathing oxygen from the air while living in pools of stagnant water.
Figure 1. Hover flies come in all sizes, shapes and colors.
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| Figure 1A. Toxomerus. Photo courtesy of Patrick Alexander (Creative Commons). | Figure 1B. Merodon. Photo courtesy of Cheryl Moorehead (Creative Commons). | Figure 1C. Eristalis. Photo courtesy of Fyn Kynd (Creative Commons). |
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| Figure 1D. Eupeodes. Photo courtesy of David Cappaert, Michigan State University, Bugwood.org. | Figure 1E. Ocyptamus. Photo courtesy of A. Jaszlics (Creative Commons). | Figure 1F. Milesia. Photo courtesy of Russ Ottens, University of Georgia, Bugwood.org. |
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Figure 2. Diagram of a hover fly wing showing the spurious vein, a vein that runs through the middle of the wing and is open (not attached to another vein) on both ends. It is an identifying characteristic of this very large and diverse family of flies, but generally only visible with a hand lens or microscope. |
Hover flies typically overwinter as either fully grown larvae or as adults, and then emerge or become active again in the spring. The number of generations per year varies depending on species.
Adult hover flies feed mostly on nectar and pollen and can often be seen hovering around flowers. They are considered a very important group of pollinators outside of the bees. Some hover flies are attracted to the salt in human sweat and will land on exposed skin. But remember, they are harmless!
White or yellow flowers with easy-to-access nectar and pollen are especially attractive to adult hover flies and can be a good way to bring them into your home gardens, where they may choose to lay their eggs and therefore provide pest control services as larvae. Eggs of predatory hover flies are typically laid singly on plants near suitable prey. A few examples of plants that will attract hover flies are sweet alyssum, parsley, dill, yarrow, clover and buckwheat.
Be sure to also check out other Ohio State University Extension beneficial fly fact sheets about tachinid flies and long-legged flies!
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| Figure 3A. A predatory hover fly larva consuming an aphid. Photo courtesy of David Cappaert, Michigan State University, Bugwood.org. | Figure 3B. The larva of Eristalis, referred to as a rat-tailed maggot because of its long siphon. Photo courtesy of Whitney Crenshaw, Colorado State University, Bugwood.org. |
References
Bugg, R.L., R. Colfer, W.E. Chaney, H.A. Smith and J. Cannon. 2008. Flower Flies (Syrphidae) and Other Biological Control Agents for Aphids in Vegetable Crops. University of California Division of Agriculture and Natural Resources Publication #8285, pp. 1–25.
Colley, M.R. and J.M. Luna. 2000. Relative attractiveness of potential beneficial insectary plants to aphidophagous hoverflies (Diptera: Syrphidae). Environmental Entomology 29: 1054–1059.
Schneider, F. 1969. Bionomics and physiology of aphidophagous Syrphidae. Annual Review of Entomology 14: 103–124.
Vockeroth, J.R. and F.C. Thompson. 1987. Chapter 52. Syrphidae. In Manual of Nearctic Diptera. Vol. 2. Coordinated by J.F. McAlpine, B.V. Peterson, G.E. Shewell, H.J. Teskey, J.R. Vockeroth and D.M.
Wood. Agriculture Canada Monograph 28: 713–743.