March/April 2016For Wildlife Watchers: House Flyby Rob Simbeck

A single fly can carry more than a million microbes.

Leave it to Issa, the St. Francis of Japan's haiku masters, to remind us that it's possible to empathize even with a fly, if we will just pause for a close-up.

We may see them as vermin, but Issa...? Is his little fly fretting? Praying? Actually, wonder of wonders, it is bathing, much as a cat would. It rubs its legs over its head, thorax, wings and abdomen, scrubbing its eyes, antennae and the bristles on its legs and body, then rubs its legs together and against its mouth to brush away grime. It's important, since flies, like vultures, spend a lot of time around filth, and each body part is essential for finding food and drink, and avoiding predators.

Still, we associate flies quite rightly with disease and death. Their press has always been pretty bad, beginning with the Bible, as they were one of the plagues of Egypt. Also, the word Beelzebub translates literally as "Lord of the Flies." Not exactly a ringing endorsement.

It's worth noting that North America was once without them. The house fly is actually an Asian native that has followed humans around the globe. Both we and the animals we domesticate produce two things flies love, garbage and feces, both great nutritional sources for them and their offspring.

Two characteristics of flies make this a bad deal for us humans. First, to use the high-dollar words, flies regurgitate and defecate on pretty much everything. The former softens and liquefies food so it can be drawn in through a sponge-like proboscis. The latter is, in this case, a distressingly frequent activity. Second, they're microbe magnets, known to carry more than a hundred pathogens, including anthrax, typhoid, dysentery, cholera and E. coli. In fact, a single fly can carry more than a million microbes. Think about that when one moves from a dog dropping to your salad. Amazingly, they seem to be immune to all of them.

None of this would be of much consequence if they reproduced at the rate of, say, pandas or polar bears, but short-lived creatures tend to make young while they may. Flies are ready to mate quite young - at about twenty-four hours after birth for females and as few as sixteen for males.

"Being slightly smaller, males may develop slightly quicker than females in the same conditions," says Eric Benson, an extension entomologist and professor of entomology at Clemson University. "Females only mate once, and it behooves the males to be ready and able to mate before the females fully develop so they can get the girl of their dreams."

Females lay from 75 to 150 white eggs, in a location that is moist and nutritional, several times over three or four days, laying five hundred to six hundred eggs altogether. Just a millimeter long, each egg can hatch in eight to ten hours in very warm weather into a smooth white maggot, which begins eating and grows to two-fifths of an inch in three to five days, looking ultimately like a wriggling grain of white rice.

The maggots shed their skin several times, then crawl to somewhere cool, dark and dry. There, they turn into pupae, their hard brown shells offering protection. In three days to three weeks, they develop legs, wings and all the rest in a process as fascinating and mysterious as that of the butterfly, whatever we think of them aesthetically. The adult breaks through the case and emerges full-size, about a quarter of an inch long, and does not grow after that point. The entire cycle - from egg to adult - can take as little as a week, with three weeks being the average.

The house fly's head swivels on a small neck and is dominated by two reddish eyes, each with 4,000 six-sided lenses working independently and providing wide-angle vision that give it a great advantage in fleeing predators - as do the hairs all over their bodies.

"House flies are very good fliers," says Benson, "but they are covered in an exoskeleton, which is like flying in a suit of armor. The hairs help them process and evaluate information in their environment. Many probably detect air currents, direction and speed. Hairs on the antennae would detect odors for food. Hairs on their tarsi (feet) function as ‘taste buds.' This is why flies often walk around in circles when they land on food."

The fly's body is divided into thorax and abdomen, the former gray with four longitudinal stripes and home to the wings and legs, the latter yellowish with a dark median line. Its veined, transparent wings can beat two-hundred times per second in a figure-eight pattern, and 11 percent of its total body mass is dedicated to the muscles that drive them. It can fly at five miles per hour and travel a couple of miles, if necessary, to find food and water. Most insects have four wings, but house flies are from the order Diptera, meaning "two winged" The other pair gradually evolved into knobbed filaments that aid in stability.

A fly's six segmented feet have curved claws and wet, sticky hairs that allow them to cling to pretty much anything - horizontal, vertical or upside-down. A 1945 study sought to learn how they landed on ceilings, and slow-motion film showed they used a half roll rather than an inside loop. To disengage, they twist and pull each foot free.

Everything is pretty primitive here - a fly's brain is essentially a big nerve mass called a cerebral ganglion; the digestive system a long, busy tube; the respiratory system a number of tracheal tubes branching from pores called spiracles - but it's enough to do the trick.

Given their reproductive rate, if all of the descendants of a single pair lived, they would cover the Earth to the height of a three-story building in just a few months. Fortunately, spiders, beetles, mites, birds, frogs and other reptiles eat them, as do parasitic wasps that burrow into the shells of the pupae. Most never really get going; less-than-ideal conditions - too wet, too cold - often inhibit or stop development of eggs, larvae and pupae.

While roaches, termites, ants and bedbugs are "probably more important pests than house flies," Benson says, "fly control in restaurants and food prep areas is extremely important and ongoing. Flies in general, and house flies specifically, can get out of control quickly, so, compared to other pests, house flies can become the most important pest in a structure literally overnight."

It doesn't take many to repopulate an area if conditions are right. And so, while we may not get to Issa's level of contemplation, as wildlife watchers it may behoove us to cast a more appreciative eye their way when we, as we inevitably must, interact with them.

Rob Simbeck is an award-winning freelance writer living near Nashville, Tennessee.