Probably more than all other insects, flies have managed to attract human attention. We just can't seem to avoid or ignore these two-winged insects, especially the species known as the house fly.
In fact, even as I compose this on my trusty laptop – on one of the coldest days in years here in Indiana – a small fly intrudes. It zoomed past the screen of my computer, making not one but two passes, as if on some sort of reconnaissance mission. Searching for what I do not know. Food? A mate? A place to rest?
After the second pass, it landed on the plastic rim of the screen and marched upward before resuming flight. It hasn't returned. It didn't hang around long enough for me to determine for sure what type of fly it was.
It was probably a fungus gnat, one of those fruit fly-sized flies that sometimes surprisingly show up in homes during midwinter. That is because fungus gnats feed as larvae in high organic material, such as the soil in house flowerpots or debris in the trap of sink drains.
Because flies are some of the most common of insects, humans in general and entomologists in particular have always had to deal with them. L.O. Howard, who became chief of the Division of Entomology, U. S. Department of Agriculture, in 1894, was no exception. In 1901 he published a book on entomology. That book is entitled The Insect Book: A Popular Account of the Bees, Wasps, Ants, Grasshoppers, Flies, and Other North American Insects Exclusive of the Butterflies, Moths and Beetles, with Full Life Histories, Tables and Bibliographies. As you might have guessed, the book is generally known just as The Insect Book.
Howard discussed a number of flies in The Insect Book, including mosquitoes, moth flies, gad flies, horse flies, bee flies, robber flies and dance flies. He also devoted space to what he called "The House Fly and Its Near Relations." Howard, in 1911, published an entire book on the house fly called The House Fly - Disease Carrier. He suggested that typhoid fly was probably a better common name because this fly can transmit the bacteria that cause typhoid fever on its feet.
The house fly and all other true flies are classified in the order Diptera. The word diptera means “two wings.” True flies are the only major group of winged insects that possess two, not four, wings.
In Diptera one pair of wings has been replaced with structures named halteres. Halteres can best be described as knobs on stalks that function as balancing organs in the fly. Think of halteres in terms of the long pole that high-wire walkers carry to maintain their balance. Halteres are essential to flight of the fly. Flies that have had their halteres removed cannot fly.
Flies, especially the ubiquitous house fly, have been immortalized by many a writer. American Entomologist Vincent Dethier authored a delightful treatise on scientific experiments using the house fly. The book, To Know a Fly, was published in 1966.
Even William Shakespeare noted flies in a play or two. In "Romeo and Juliet," he writes: "more courtship lives in carrion flies than Romeo." The lines, "As flies to wanton boys are we to the gods. They kill us for their sport," appears in "King Lear."
The title of one of Emily Dickinson's more famous poems is "I Heard a Fly Buzz When I Died." William Blake compares his own life to that of a fly in his poem, "The Fly." But for most of us, poet Karl Shapiro captures our attitude about these insects in his poem, "The Fly," with the lines "But I, a man, must sway you with my hate, Slap you across the air and crush your flight."
But leave it to the master of American whimsical verse, Ogden Nash, to ask the ultimate question about the value of flies. He poses the question in his poem, "The Fly." The poem goes "God in his wisdom made the fly and then forgot to tell us why."
OK, Ogden, here are three good reasons for flies: they provide food for a lot of animals and some plants, such as the Venus fly trap; they dispose of dead plants and animals (through what they eat); and a few of them pollinate plants. Even the despised house flies have a good side!