Fly Facts: From Horseflies to Fruit Flies, We've Got You Covered

Taking into account a few fly facts, these pesky pests offer a fascinating, albeit odious, view of the insect world.

Close-up of Fly Eyes

No wonder these creatures have such good vision.

iStockphoto.com/Gewoldi

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Wouldn’t harm a fly, huh?! Bet you would if you knew just how unpleasant these insect pests can be. Like mailboxes and roadside weeds, flies come with the territory when you live in the country. And if you have livestock around, your odds of encountering them increase sharply. You can swat at ’em, spray ’em, chase ’em out of the house or hang pest strips in the barn, but you’ll never get rid of ’em. So, from horseflies to fruit flies, you might as well learn a few fly facts and learn to coexist.

Ever wonder why it’s so difficult to hit a fly with a swatter? It’s their incredible eyesight. Flies have compound eyes containing more than 4,000 photo receptors, or lenses, in each eye, allowing them to see in almost any direction at once. Couple that with their ability to switch flying directions in midair, and your poor batting average begins to make sense. 

Entomologists say more than 18,000 fly species are found in North America, with 120,000 species worldwide. They divide flies into five groups, including biting flies, filth flies, small flies, overwintering flies and gnats. 

Biting flies are the vampires of the fly world. The more than 300 species include the black fly, stable fly and deer fly, though the bite of the horsefly is one of the most painful. Horseflies are equipped with scissor-like mandibles that tear and cut. While the males feed on pollen, the females feed on blood to assist in egg development. Left uncontrolled, swarms of deer flies and horseflies can madden horses and cows. In as little as six hours, 20 to 30 of these flies can withdraw almost a third of a pint of blood from their victims, causing cattle to lose as much as 100 pounds of weight in a single season, and reducing milk production by up to 30 percent. 

Biting flies can spread diseases such as conjunctivitis, poliomyelitis, typhoid fever, tuberculosis, anthrax, leprosy, cholera and dysentery. In sub-Saharan Africa, tsetse flies are responsible for transmitting the protozoa that can cause sleeping sickness. According to the World Health Organization, as many as 70 million people are threatened by the disease, with tens of thousands of new cases each year. Black flies are also responsible for causing River Blindness, affecting millions of people in Africa and Latin America.  

Filth flies feed and lay their eggs in trash, animal feces and decaying material. While they don’t bite, they are known carriers of more than 100 diseases, including cholera, malaria and anthrax. This group includes the common housefly, sewage fly, phorid fly and face fly, which is a common problem for livestock. Face flies constantly alight around the eyes, nose and mouth of cattle, feeding on their tears, saliva, mucus, blood and excrement. Livestock subjected to face flies may stop feeding, and face flies are known to spread pinkeye in cattle. 

Filth flies can carry thousands of bacteria on their feet, so when they alight on your sandwich, you’re eating whatever it was they last landed on. Sometimes people refer to something insignificant as a flyspeck. But a flyspeck isn’t so insignificant when you consider that flies can defecate every 4 to 5 minutes. 

Flies are among the most prolific of all creatures. Entomologists at Ohio State University in Columbus say a pair of houseflies can produce five to six hatches, each with 100-plus eggs. They project that if that pair began producing eggs in April, and all flies survived, theoretically they could produce  191,010,000,000,000,000,000 (191 quintillion, 10 quadrillion) offspring by August. 

The small-fly family includes fruit flies, with adults measuring a mere 18 inch in length. A fruit fly completes its entire life cycle in just eight to 10 days. The Hessian fly is another small fly that has caused millions of dollars of damage to U.S. wheat crops ever since it was brought to this country by Hessian soldiers fighting with the British during the Revolutionary War. 

Did you know flies taste with their feet? Scientists say their “taste buds” are 10 million times more sensitive to sugar than the human tongue. Many flies have tongues shaped like a straw, allowing them to suck up wet or decaying matter. 

Overwintering flies include cluster flies, which often overwinter in attics or upper walls of homes and buildings. The larvae are earthworm parasites, and adults commonly breed and reproduce in lawns and gardens. 

Unlike other insect species, flies have just one pair of wings, which can beat more than 200 times per second. Most flies don’t venture more than a mile or two from their point of origin, but black flies are known to travel as far as 10 miles in search of a blood source. 

Gnats are the smallest of flies and include biting gnats (sometimes called no-see-ums), midges, sand gnats and sand flies. Sand flies transmit a parasitic disease that causes rashes and sores, a problem for U.S. troops serving in Iraq and other areas of the Middle East. A swarm of gnats is known as a “ghost” of gnats. 

So, do flies serve any useful purpose? Well, yes, some of them do. 

Most species of flies aid in the decomposition of organic matter. Without flies, bacteria, beetles and other insects, we’d be up to our eyebrows in garbage. Fish, birds and lizards feed on certain species of flies, although the mayfly, considered a favorite for trout, is not a true fly. 

The fruit fly is widely used in scientific experiments involving genes and chromosomes. Some flies serve as pollinators, and the larvae of some flies feed on aphids. Forensic entomologists sometimes rely on the presence of blowfly larvae to establish time of death in murder cases. And physicians sometimes use disinfected fly larvae, or maggots, in debridement therapy to treat burn victims. 

By the way, did you know that the phrase “flyblown” is an old English term referring to meat
infested with maggots?
 

From Parkville, Missouri, cowboy poet Jerry Schleicher has been known to stop a car to chase away a pesky fly.