Bioblitz
Joy of Flies
Before reaching for that swatter this summer, consider how our most misunderstood insects rival bees as crop pollinators and serve as powerful tools in a number of human pursuits, from solving crimes to unraveling the nature of life.
By Frank Graham Jr.

“God in His wisdom made the fly / And then forgot to tell us why.”—Ogden Nash

We stand in clusters of half a dozen or so above the rocky beach fringing a small cove in eastern Maine, long-poled nets and killing jars at the ready. Fog is sifting in from the cold offshore waters. Gulls sail overhead; a raft of eiders undulates on the cove’s rippled surface. “Keep your nets low,” calls Joe Keiper, curator of invertebrate zoology at the Cleveland Museum of Natural History and the expert brought in to lead the assault on our winged prey. “Sweep just over the rocks and dead seaweed. There are lots of flies in there, and they’ll pop up.”

Standing uncertainly on a surf-tumbled chunk of granite, I swish my aerial net over windrows of rockweed stranded by the tides. Sure enough, several small dark forms flit inside the net’s folds. “Seaweed flies,” confirms Keiper. “Coelopa frigida.”

The “Diptera Blitz” began on a Saturday afternoon last July on the Schoodic Peninsula in Maine’s Acadia National Park. There were 42 of us—some professional entomologists, others serious amateurs—registered for this 24-hour inventory of the park’s population of Diptera, or two-winged flies. Biologists know a great deal about the birds, mammals, fish, and plants within the park’s boundaries but little about the invertebrates. And even among the insects, flies are the invisible animals—unless, of course, they whine or bite. Intensive yet inexpensive, the volunteer-powered blitz was designed to give the biologists some clues to the diversity of these little-known animals they have been assigned to preserve for the future.

“You glance at a fly and you see just a speck,” Keiper had said on our way to the cove. He is slender and youthful looking, with a dark circlet of beard and mustache compensating for a retreating hairline. “But when you begin to look closely at it, to observe its behavior, you realize it’s an interesting animal. You don’t have to be an expert to go on and learn more about it. Flies offer diversity, morphology, nesting biology, cool stories—and a lot of services to us humans.”

As its name implies (Diptera—from Greek components meaning “two-winged”), this order of insects differs from all others, such as the dragonflies, beetles, or butterflies, in which the vast majority of adult individuals possess four wings. Yet flies are the most acrobatic of fliers. Evolution gave them two pairs of wings like other insects. Then, far back in time, it took away the second pair and replaced it with two stumpy appendages called halteres. Similar to gyroscopes, the rotating halteres help give flies balance and their stuntlike aerial ability to hover and even fly backward. These are the true flies.

Biologists have so far described more than 25,000 North American species of Diptera, assigned to 108 families (with some researchers arguing for full family rank for several additional, hard-to-place groups). Clearly, by numbers alone, Diptera are an important assemblage of animals affecting humans in a variety of ways but which most of us know only through the handful of families we regard with repugnance: Mosquitoes serve as carriers of malaria, yellow fever, West Nile virus, and other nasty diseases. House flies spread filth. Black flies and horse flies bite something fierce.

But among the Diptera, as in most groups of animals, those we brand the bad actors are in a minority. Scientists recognize flies as key players in ecosystems, recycling carcasses, dung, and plant debris while themselves serving as vital food in the life cycles of many kinds of birds, bats, and fish. Some rival bees as pollinators of domestic crops. Other flies are powerful tools for helping geneticists unravel the nature of life, the police in solving violent crimes, or pollution control specialists in assessing the quality of our waterways. And, more than most people realize, flies are glistening ornaments in our parks and gardens.

The Diptera Blitz, organized chiefly by Acadia National Park and the Maine Entomological Society, is happening around the clock in alternating fog and murky sun, at night in the glare of vapor lights on white sheets set out as inviting backdrops, even at dawn on the inside walls of a cabin or dining room. A few of the collectors, like Joe Keiper, bring expertise; others bring a simple fascination for things wild and strange.

“I didn’t want to miss the blitz here in Maine,” Jessica Rykken, one of the participants, tells me. She is 42, fair-haired, slightly built. Rykken, a doctoral fellow at Harvard’s Museum of Comparative Zoology, carries out inventories of insects, spiders, and other small invertebrates on islands in Boston Harbor managed by the National Park Service. “I’m learning about fly taxonomy here, and I’ve met some Diptera experts like Joe Keiper who will help me identify specimens I’ve picked up in my work.”

Wielding a net nearby is Dana Michaud, the quintessential amateur. Like many Maine residents, he is of French-Canadian descent. Michaud works the night shift as a water-quality specialist at a paper mill in central Maine so he can roam the woods and fields in search of insects by day. (“I began raising caterpillars and collecting beetles years ago, when I was a boy,” he tells me.) Across the road is Richard Hildreth, wearing overalls and a shaggy white beard, a retired businessman who spends much of the year as a volunteer monitoring birds, plants, dragonflies, and just about any other wild organism for the Maine Coastal Islands National Wildlife Refuge. Kevin Tloczynski, 28, served in Iraq as a medical officer with the U.S. Air Force. Now a civilian, he is pursuing a degree in environmental science at Cleveland State University and is one of the six grad students Keiper has brought with him to the blitz.

Participants return from marsh, bog, and forest with jars full of flies, the specimens long since put down with ethyl acetate or other killing agents. Nipped by mosquitoes or gouged by thorns, the collectors pause briefly for meals and a little sleep, but their enthusiasm never flags. As Lynn Havsall, an environmental educator at the College of the Atlantic in nearby Bar Harbor, remarks, “Time’s fun when you’re having flies.”

David Manski, the park’s chief of resource management, logs in each participant’s take at a park building, gives it a number corresponding to the specific place where it was collected, and sends it on to a makeshift lab nearby. Knowledgeable dipterists stationed at microscopes then begin sorting and identifying the specimens. “It’s tough working with the tiny ones,” Tloczynski comments wearily. “But I get a lot of satisfaction from pinning mosquitoes.”

A preliminary count shows that more than 260 species, representing 50 of North America’s 108 dipteran families, are already represented on dark insect pins in the park’s new collection. Manski looks delighted. “We can’t manage our resources unless we know what’s here,” he says. “We’re trying to do one blitz a year—one year on beetles, another on butterflies and moths, next year spiders. A lot of us wish there would be more detailed inventories of local wildlife, but as a rule the funds just aren’t there.”

I take my turn at a microscope, using a picture key in entomologist Stephen A. Marshall’s big book, Insects: Their Natural History and Diversity, to narrow my flies at least to the family level. There are several possible shortcuts to this end, including thumbing through Marshall’s book to find a lookalike among the extensive photos. I choose an even easier route, armed as I am with the answer Keiper had given me at the shore. Plucking a smallish fly from my killing jar, I lay it on the scope’s platform. Out of focus, it looks like a clump of shoreline debris.

Then, as I turn the scope’s focusing knob, the “clump” slowly metamorphoses under the fiber-optic light. The parts blossom from a blur into a coherent, bristle-studded whole—legs, prominently veined wings, and a flattened head, from which the enormous, many-faceted eyes reflect only a muted glow from the manmade illumination. “Not ant-shaped,” the key prompts me. “Palpus present. Posterior spiracle without bristles.” Sure enough, in another step, the key leads me to my destination: “Strongly flattened bristly flies found on seashore algae: Coelopidae.” Turning to Marshall’s description alongside the photo of a familiar-looking fly in the text, I read: “FAMILY COELOPIDAE (SEAWEED FLIES) . Coelopa frigida is the only northeastern species of the Coelopidae, a family of flies found on seaweed-strewn coasts around the world. Larvae develop in piles of rotting seaweed, or wrack.”

Despite, or more accurately because of, the problems Diptera pose to both the physical and economic well-being of our own species, the blitz offers me a rare opportunity to learn something about their biology. Or at least to dispel some of my confusion.

Like most people overwhelmed by the abundance of insects, I grasp at any crutch the pros offer to make sense of the orders and families. Butterflies, dragonflies, and many other four-winged “flies” don’t much resemble Diptera. They are insects, yes, but placed by biologists in other orders. Casual observers, ignorant of science and not bothering to count the number of wings, made up most of the common names for all kinds of insects and stuck on the word “fly” because—well, probably just because they were flying around. The late Donald Borror, a prominent entomologist at Ohio State University, was among the experts who advocated a nomenclatural means of clearing up the confusion.

“When a fly belongs to the order Diptera, the ‘fly’ of the name is written as a separate word (for example, black fly, horse fly, and blow fly),” Borror explained in the popular textbook An Introduction to the Study of Insects. “When it belongs to another order, the ‘fly’ of the name is written together with the descriptive word (for example, dragonfly, butterfly, sawfly).”

But flies, under any name, have always posed a conundrum for the optimists among us. Ogden Nash seems to have best articulated the popular view with his epigrammatic verse: God in His wisdom made the fly / And then forgot to tell us why.

Modern biology has relieved the Creator of responsibility in this case, teasing out the evolutionary details in the eons-long passage of primitive, wingless invertebrates to the present remarkable, if sometimes pernicious, group of animals I am now helping to “blitz.” The first four-winged insects (the only invertebrate animals to develop powered flight) appear in the fossil record dating back more than 350 million years. Two-winged flies show up 215 million years ago, having evolved the tiny, clublike hind wings called halteres to make flight with the front pair more efficient. (The most agile fliers among the other orders, except for dragonflies and damselflies, generally link their fore and hind wings, effectively mimicking the agility of the dipteran two-winged flight.)

Evolution has tinkered with this apparently rigid blueprint to produce an astonishing variety of adaptive detail. Traditionally, biologists classified the Diptera into two large groups based on the shape of the antennae—“long-horned flies,” typified by the mosquito, and “short-horned flies,” resembling the house fly. This distinction remains a handy way to make sense of the order but, by naming names, emphasizes its “bad guy” image. As we blitz, we struggle to bypass that connotation and see these diverse insects for what they really are.

Mosquitoes, however, force themselves on us, both indoors and out. The scientific names of some individual species are provocative enough: Aedes irritans, Aedes excrucians, Psorophora horridus, Culex perfidiosus. The taglines express the underlying threat, for mosquitoes are arguably the most dangerous of all multi-celled animals. Different genera and species serve as carriers of organisms that cause malaria, yellow fever, and a couple of hundred other unpleasant diseases. Only the female “bites.” Technically, she slices through the human skin with her bladelike mouthparts, spewing an anticoagulant into the wound and often, as collateral damage, one of those microscopic disease organisms as well. The mosquito then siphons the blood to nourish her offspring. Adult males can claim innocence, even wisdom, spending their time sipping nectar and hunting for sex.

An array of other bloodsucking flies exists—black flies, horse flies, and biting midges (often called “no-see-ums”) among them. Rivaling mosquitoes in villainy are the tsetse flies of Africa, carriers of sleeping sickness. But contrary to folk entomology, the house fly does not bite, bearing mouthparts designed to sponge up and liquefy its meals. If you believe you were bitten by a house fly, the perp was probably the similar stable fly.

Bloodsuckers are in a minority among the Diptera, though farmers compile their own list of flies they love to hate. Tephritid fruit flies, including the Mediterranean fruit fly and apple maggot, terrorize fruit growers. The Hessian fly and various root maggots devastate their own share of crops. Yet many dipteran families exert little or no impact on humans, so we consign them to oblivion. The Empididae, or dance flies, harm nothing we care about, and few people have ever heard of them.

The good news is that many fly families redeem their wayward relatives. The Drosophilidae include the insects indispensable to geneticists as experimental animals because of their small size, giant salivary chromosomes, and the ease with which researchers can culture them in great numbers. Often called little fruit flies, they are placed in a different family than the Mediterranean fruit fly, and tend to feed on fungi and juices found on overripe fruit rather than attack a ripening crop.

Though lesser known, a host of other flies prove useful in human pursuits. Chironomid midges (the non-biting kind) are always present around water and thus become one of the most reliable tools in determining its quality. Because of the wide and consistent range of tolerance levels across the family, experts can gauge the extent of waste matter in a body of water by the kinds of midges they find there. One species may be able to live only in clean water, another in total gunk. For instance, a single species often becomes dominant in rivers degraded by heavy metals or sewage. Why? That species may be adapted to the rapid excretion of toxic substances, or to very short life cycles—its individuals reproducing and dying “natural deaths” before the pollution disables them.

We give bees much of the credit for pollinating crops, but research also demonstrates the importance of Diptera in agriculture. Small flies were actively pollinating plants in the early Cretaceous (65 million to 140 million years ago), before the general spread of bees and moths around our planet. Leading the list of modern pollinating Diptera are the Bombyliidae, or bee flies, often confused with bees and like many of them equipped with a long tongue to reach the nectar and pollen deep in flowers. Flower flies and long-legged flies are also effective pollinators.

Human ingenuity has put the insects to work for us in the most precise ways, in one area taking advantage of their capacity as sanitary engineers (consumers of dead plant and animal matter) to turn them into crime fighters. Forensic entomology (a branch of medical jurisprudence) depends on a detailed knowledge of the life histories of insects; blow flies are one of the star witnesses when it comes to presenting evidence in court. Often called blue bottles, green bottles, and the like, they are attracted to a corpse by the breakdown of its muscles shortly after death and lay their eggs in various body openings. The maggots hatch in a matter of 24 hours and feed internally, hastening decomposition. Entomologists able to identify maggots that are present on a body can gauge their rate and stage of development in the context of environmental conditions, thus helping to establish the time and place of a victim’s death, or even a body’s successive whereabouts in the time before it was discovered.

During early June some years ago, the presence of shore fly maggots (Coelopa frigida, the same fly I examined under the microscope) enabled authorities to trace the convoluted route taken by the body of a sailor found floating in the Baltic Sea. Entomologists showed that the body had been stranded for a time along an algae-strewn shoreline. The age of the maggots found on the body pointed to early May as the period of shoreline exposure, while the absence of blow flies (because the weather at the time was too cool in that region) helped to confirm the date.

Joe Keiper shrugs off the more dramatic forensic feats served up on TV crime shows, though his work with flies is occasionally hair-raising. Because of his position at the Cleveland Museum of Natural History, hospital staff or the local coroner often call on him to help with a puzzling case. On one occasion doctors treating a young girl for a serious eye infection asked him to clear up a medical mystery.

“The doctors had removed a live maggot from under the girl’s eyelid, where it was feeding on tissue,” Keiper recalls. “They wanted to know how in the world the maggot got where it was. I identified it as a warble fly, which ordinarily bores into live rodents and similar animals. That gave us a clue, and under questioning, the girl remembered visiting a petting zoo, where she had handled rabbits.” Bingo!

Sometimes Keiper’s work brings him face-to-face with tragedy. Several years ago the police discovered the mummified remains of an old woman in an apartment where her daughter still lived. “In examining the body, they found pupal cases left by maturing flies,” Keiper said. “I was able to identify the species from the cases and, because I knew the season when those flies mature in the Cleveland area, I could estimate how many months since she had died. The evidence ruled out foul play. The daughter had developed severe Alzheimer’s disease and just hadn’t noticed that her bedridden mother was dead.”

Observing Diptera leads to satisfactions of many kinds, including Keiper’s “cool stories.” But for me the joy of flies comes chiefly from the beauty they lend to the world around us—specifically, to meadows and ornamental gardens. The Syrphidae, or hover flies, are gemlike insects garbed in velvety reds and blacks and golds, rivaling hummingbirds and butterflies in bringing to vivid life the masses of plants in bloom. When I browse among flowers, with flies hovering just over Potentilla and bee balm, I bend to catch the light on their whirring wings, the air around them shimmering in their reflected glow. A few feet away the sun transforms a tiny metallic long-legged fly into a jewel on the fresh green of a Delphinium leaf—our garden’s pygmy tiger stalking a prey my eyes can barely see. Midges, a golden mist, dance overhead in a shaft of sunlight they have made their own.

Learning to distinguish and name the chief families in the Diptera at the blitz has only added to my satisfaction while observing them in the garden. Someday, perhaps, I will encounter a stranger on a Maine beach as he watches flies buzz over a clump of dead seaweed. Mimicking Keiper’s pronunciation and quietly authoritative voice, I will finally have a chance to drop my bombshell: “Seaweed flies. Coelopa frigida.”

What You Can Do

Bioblitzes are all the rage these days among wildlife-savvy citizen scientists. Most are fully volunteer efforts that take place over a 24-hour period, often with the help of experts. The E.O. Wilson Biodiversity Foundation is supporting selected microbial bioblitzes in 2007 (contact info@eowilson.org), and developing a bioblitz how-to manual scheduled for release in 2008, as well as a program for teachers to follow. For additional information, links, and discussion groups that can be helpful when organizing a bioblitz, visit www.pwrc.usgs.gov/blitz.

Banking on Bioblitzes
A Q&A with the eminent biologist E.O. Wilson, who is one of the founders of the bioblitz phenomenon. Wilson discusses, among other things, how blitzes can be a valuable tool for conservation.