THE HOUSEFLY HAS MADE A PEST OF HIMSELF
FOR 25 MILLION YEARS
CHICAGO - Try to recall those two houseflies you saw hanging around during the first really warm days of April.
Though entomologists, and anyone else who happens to speak Latin, would call them Musca domestica, let's call them Fran and Fred.
Further, imagine they were the only flies in existence, so when their four eyes' 16,000 facets first met, it's understandable why their 10 hearts beat as quickly as Buddy Rich did in his prime.
Instinctively, Fred likely mounted Fran, with her blessing, somewhere on the ground. Copulation, say entomologists, apparently never takes place in the air, though more than one male has been seen attempting a hijack.
After a split-second of fly foreplay - caressing her head with his forelegs, to which she responds by extending her genitalia to his - they mate, anywhere from a few seconds to a couple minutes before Fred buzzes off.
Within a week, Fran will lay the average 120 eggs in whatever rich, warm organic matter she finds - since houseflies, unlike the iridescent green bottle flies you`ll find around outdoor garbage cans, aren't big meat eaters, horse manure is ideal.
During the next 12 days, her eggs will undergo the complex metamorphous passage to larvae, then maggots, then pupae, finally emerging as fully-grown, 1/4-inch adults. There are no baby houseflies; any smaller ones you see were underfed as maggots or are another species.
Two weeks later, when Fran and Fred have reached the golden days of their typical one-month lifespan, they'll be grandparents several thousand times over.
By the end of August, if all their descendants were to survive the summer, you'd think twice about that Labor Day picnic. Depending upon which statisticians' fly facts you choose to believe, the planet would be covered to a depth of 23 to 47 feet.
Fortunately for us, says Bernard Greenberg, professor of biological sciences at the University of Illinois at Chicago and an internationally recognized authority on flies, these real good reasons for window screens don't get to realize anything near their potential:
* The fly's natural enemies - birds, reptiles and certain other insects, not to mention those Venus flytraps that show up at your grocer's every spring - eat their fair share.
* And unless there's sufficient food, warmth and moisture throughout the eggs' development, those maggots don't have a chance.
* Because they're tropical animals, temperatures also greatly affect an adult's life - and with it, if not their ability to reproduce, at least the likelihood of getting around to date.
At 53 degress they're airborne; at 48 degress, they`re reduced to a crawl; at 44 degrees, they're virtually comatose; and at a few degrees below freezing, it's death within hours.
If it climbs much past 102 degrees, heat paralysis sets in; at 116 degrees, death comes almost as swiftly as with a swatter. It's the low 90s in which these critters thrive.
And they've been thriving for a while now, "at least 20 or 25 million years," says Greenberg. Even so, after all that time, they haven't gotten any better looking.
Their diminutive size (coming about 100,000 to the pound) and aversion to being petted doesn't give us much of a chance for a really good look at them or many of the other approximate 87,000 species in the diptera order, that grouping of all two-winged insects.
It took the 1958 horror film "The Fly" to show us
what beasts they really are. Al Hedison, playing yet another scientist
carried away exploring the mysteries of life, accidentally swapped
heads with the title star. Not a pretty sight.
Mouse-gray and loaded with short stubby hairs (as are the fly's other two body parts, thorax and abdomen), the head can rotate nearly full circle and is dominated by two colossal purplish-brown eyes, each made up of 4,000 six-sided lenses, all of which work independently.
While they see all colors except red, Greenberg says, flies are rarely guided by their fragmented sight alone. They rely on two short, thick antennae set between the eyes to detect air movement (an approaching swatter, for instance) and smell food.
(They will, by the way, eat just about anything liquid or easily liquefied, though they have a decided preference for hot meals, and a special need for sugar and protein.)
At the head's base is the mouth, the proboscis, a retractable funnel-like device nearly as long, and just as unsightly, as the head itself. From our standpoint, its most endearing quality is that it can be used only as a vacuum. Houseflies don't bite.
(Stable flies - resembling the housefly in size and color - do. They're the ones, Greenberg says, "that attack your ankles at the beach," and both sexes are out for blood.)
The worst offender, however, is the female horse fly. (Males are harmless.) Three times the gentle Musca's size, her pointed proboscis can pierce leather and draw up to 100 cubic centimeters of blood on a good day.)
As any reasonably coordinated 10-year-old can tell you, the housefly isn't terribly swift, despite the fact that those wings beat 200 to 330 times a second (research findings differ).
With an average speed of 4.5 miles an hour, he can, however, just keep up with a walking horse. And because wing muscles account for 11 percent of his body weight, he can trail that horse for hours. Another example of nature's delicate balance.
The fly's six feet make possible those seemingly effortless wall walks and ceiling climbs. He either grabs rough surfaces with each foot's pair of curved claws or uses the continually wet and sticky tiny glandular hairs at their tip.
For years researchers were divided over how flies managed to land on ceilings. One camp claimed they performed an inside loop. Another said they executed a half-roll as they neared the surface.
E.D. Eyles of Kodak Research Laboratories in England, cleared it all up in 1945 after filming the feat in slow motion: half-roll it was.
An issue they're still divided on, Greenberg says, is where in the world they all come from each year. "Most likely they've been here all winter, surviving in animal houses, dairy barns" and the like. "They, like cockroaches, can survive in the coldest part of the world as long as man's there to provide a home."
But another theory says migration is the answer. Greenberg thinks "both are probably true."
"They're not native Americans. When man came around, the fly hopped a ride. They probably came over with Columbus, or before. Before the 1300-1400s, we may not have had any flies at all."
But all flies, like man, he says, "probably got their start in Africa. You'll find the greatest number of species and sub-species there."
You'll also find there the greatest danger of fly-borne disease. Those horrid television images of Ethiopia's starving, too weak to wave away the dozens of flies feeding on their eyes' and lips' moisture, brought that home. "In our sanitized, plastic-wrapped society, fly-borne disease is a relatively unimportant thing," says Greenberg, author of a two-volume treatise on the subject. "Especially since we stopped using the horse to get around."
"But in Mexico, too - all of Latin America really - these countries are loaded. They're struggling at a very primitive level."
Parts of the U.S. fair no better.
Some researchers say it's possible for a single city slum fly to carry as many as 33 million bacteria internally and have another half billion swarming all over its body. Among the possible diseases carried: typhoid, cholera, dysentery, salmonella, polio and several parasitic aliments like tapeworm.
But the danger, Greenberg points out, rests more with the community than on the back of the fly: "The cleaner the neighborhood, the relatively cleaner flies you`ll have.
"But people in (upscale neighborhoods) shouldn't feel so smug
- they do
Fortunately, disease-causing bacteria are highly vulnerable to even the slightest light and temperature change. So the trip to the table, no matter how short, is a difficult one.
Even so, most researchers agree, this common pest does pose a potential health problem, and not only because he's likely to land on Dalmatian dung one minute, then dance on your doughnut the next. While their feet are filthy, their manner of dining is even more dangerously disgusting - a fact they almost seem conscious of. Why else then would they so thoroughly wipe their hands and face after eating?
While exploring solid or semi-solid surfaces - like candy, corn flakes or your mashed potatoes - the first thing they'll do is cough up some of their last meal. This mixes with and helps dissolve the new find, most of which then gets sucked through the proboscis.
Most, though, is the best they can do. A fly always leaves a little something wherever he's been. Just another reason why "Hey, waiter!" jokes aren't funny.
Despite our most determined efforts, houseflies continue to resist any meaningful long-term control. We came close right after World War II though, when DDT and other potent chlorinated hydrocarbons were used extensively in homes, restaurants and dairy barns. Only later did we realize some flies developed immunity, passing the trick on to their kids, while we poisoned ourselves in the process.
"No spray is absolutely safe," Greenberg says. "If it can kill an insect, it can damage us."
By far, the safest and best approach to summer fly control is preventative - cleaning up after the dog and keeping a tight lid on the garbage - to at least cut down on the filth in which they feed and breed.Some of us wouldn't want the housefly wiped out anyway. There's still enough hunter lurking in our reptilian brains to appreciate an occasional kill. Especially midair on the very first swat.
This article first appeared in the
Chicago Tribune on June 5, 1986
© 1986 Hyde Park Media
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