BUG OF THE MONTH: April 1995
Those Amazing Hover Flies
Order Diptera, family Syrphidae
Copyright © 1995 by Dave Pehling
This article originally appeared in Scarabogram, April 1995, New Series No. 180, pp. 2-3.
"Hover Flies" (a.k.a. "Drone Flies," "Syrphid Flies," etc.) are a family of true flies (order Diptera) that are common in North America and worldwide.
|Left to right, Milesia virginiensis; Eristalis occidentalis; Volucella bombylans; Polydontomyia curvipes; Spilomyia quadrifaciata. Illustrations from Howard (1903).|
Hover flies are a diverse family and are found in many habitats. Many people recognize the familiar "flower fly" that pollinates flowering plants and whose pointy-headed offspring (maggots) blindly tap their way through the foliage searching for juicy aphids and other small, soft-bodied insects. The adult "flower fly" and many other syrphids are bee/wasp mimics, sporting the typical yellow and black warning markings common to bees and wasps (order Hymenoptera). Of course, syrphids are just bluffing with these show-off colors and can not bite or sting in any way. One can easily separate the syrphid flies from bees/ wasps by 1) the typical "hovering" flight common to hover flies (they can hold absolutely still in flight - except for their wings, of course), and 2) all flies have only two wings; all flying hymenopterans have four.
|Left to right, Didea laxa; Eristalis tenax; Volucella mexicana; Ornidia obesa; Pyrophaena granditarsa; Leucozona lucorum. Illustrations from Howard (1903).|
The "beneficial" syrphid species produce aphid-eating maggots that "inch-worm" over the leaves searching for food. These larvae will occasionally nip if handled.
One of my favorite syrphids is the "rat-tailed maggot fly," Eristalis sp. The adult is a typical "hover fly" but with more honeybee-like markings. The larva is a half-inch long grub with a "tail" (actually a breathing tube) that can be extended over half the body length. These maggots are common in pools of liquid manure and heavily polluted water where they fatten themselves on the tasty, organic filth. These amazing larvae have also occasionally been implicated in cases of human myiasis (the larvae are accidentally swallowed and take up residence in the stomach or intestine, causing acute discomfort; probably not a lot of fun for the maggot either).
Cole, Frank R., and Evert I. Schlinger. 1969. The flies of western North America. University of California Press.
Howard, L.O. 1903. The Insect Book. New York: Doubleday, Page & Co.
James, Maurice T. 1947. The flies that cause myiasis in man. U.S. Department of Agriculture, Miscellaneous Publication no. 631: 1-175.