Tom Turpin
Professor of
Purdue University







Deer Flies Aren't Dear Flies

One of the real insect menaces of late spring and early summer is the deer fly. These fairly common flies are rather stout bodied. Most are about the size of, or slightly larger than, house flies. They frequently have brightly colored or iridescent eyes.

While some people might not have taken a good look at these insects, most of us have at one time or another had contact with a deer fly. Female deer flies feed on the blood of mammals. Today cattle and horses are frequently attacked. Deer are also a prime target, and that is the basis for the common name given to this type of biting fly.

Deer flies are normally encountered near streams or marshy areas because the immature flies develop in water or saturated soil. However, the adult flies can fly miles, so they're sometimes found far from breeding sites. The flies are attracted to natural light and are frequently found in windows, where they congregate after flying into a garage or house.

These flies are not gentle feeders, and that is why they are such an annoyance to any animal that is a meal target. The adult female extracts blood from a victim by first inflicting a deep gash with the blade-like portion of her mouthparts. Then she laps the flowing blood with the spongy part of her mouth. Of course, the bite is painful, and the bitten animal normally reacts by stomping, tossing its head or even running.

Deer flies also attempt to feed upon humans who venture into their habitat. The insect on its feeding forays normally dive bombs the victim. Deer flies seem to target the human head and sometimes get caught in a person's hair. All of this is very annoying, especially when several hungry flies are intent on extracting blood at the same time. This produces a scene not unlike one reminiscent of World War II, where a squadron of bombers wreaked havoc on some unfortunate city.

Humans besieged by deer flies frequently resort to a slapping or flailing behavior in an attempt to avoid becoming a meal for these bloodthirsty insects. Sometimes we even try to outrun the flies. Fat chance! Flies can cruise at nearly 30 miles per hour and seem to enjoy such a chase. Most human and deer fly encounters result in at least one fly managing to get in a bite. When that happens to humans, we can really sympathize with their animal victims. These insects are anything but "dear" flies!


Writer: Tom Turpin
Editor: Andrea McCann