Flies - Summer World: A Season of Bounty - Bernd Heinrich

Summer World: A Season of Bounty - Bernd Heinrich (2009)

Chapter 13. Flies

We breed ’em, you feed ’em.


21 June 2007. IT’S THE SUMMER SOLSTICE (IN THE NORTHERN hemisphere), and according to my calendar, which only one species goes by, it’s the “first day of summer.” But for many species summer has actually been in progress for months, and it’s now arguably the middle of summer—when the days are longest as the Earth’s axis tilts the most toward the sun. The hottest days, though, are still to come. In any case, it’s sufficient reason to celebrate, and what better way than to enjoy a dance performance?

As chance would have it, I find one. It’s right here at my camp in the Maine woods. The dance is in the outhouse, presented by a special troupe of untiring performers. I’m just a spectator today, and viewing conditions are perfect. It’s a pleasant 70°F—too cool for horse and deer flies and too dry for blackflies and the god-awful midges, the scourge from hell.

Our outhouse is open at the front, and it faces deeply shaded sugar maple woods. The dancers—two or three dozen of them—each have six long, spindly legs. They jitterbug up and down and forward and back in a dark corner just under the roof, and they are worked up to a frenetic speed. Undoubtedly they are expert performers. They ought to be. They’ve probably been doing one or another version of their act for more than 225 million years, since the Triassic period. And indeed, their performance doesn’t disappoint.

Most of the dancers are single, but several have partners to whom they are firmly attached—by their genitals. The members of a pair face in opposite directions, and when—more often than the singles—they come to rest, they dangle with one holding on to the ceiling with its front legs while the other dangles below.

The dance was still going at full throttle at one-thirty PM, when with one swoop of my insect net I went through the throng and captured about thirty of them for a closer look. (A couple of hours later there were as many there again, and they continued for at least the next two days, from about eight AM to eight PM every day. Who knows? Maybe they dance at night, too.)

Superficially they resembled huge mosquitoes. They are relatives of this group of insects, commonly known as crane flies because of their very long legs. Their bodies were about a third of an inch, while their legs were three times longer. Their legs drop off at the merest touch, an adaptation for making a quick getaway from a predator. But these didn’t get away, even as my sweep of the net left the bottom of it littered with a small pile of loose legs. These flies all looked similar, except for their genitalia. Of a pair I examined, one had a thicker but pointed abdomen, and the other a thinner abdomen with a blunt end. I presume the more ample individual was the female. Further examination under a magnifying glass revealed a tonglike clasper at the business end of the male.

By far the majority of performers at this mating dance were males. In my sample of thirty, males outnumbered females twenty-eight to two. The dance is done primarily by single males, and the females are, as among wood frogs, presumably attracted by the communal male display. A male finds a female (or vice versa), and then they mate and leave the crowd. Once a male snags a female he tends to go steady with her, for a while. To test their fidelity to each other I put three couples that I had captured in a jar. One of these pairs, which had been on the ceiling in the early morning (presumably since the night before), separated instantly. The other two pairs, captured after the dance started, stayed together for about four and five hours respectively.


Fig. 26. Preliminary notes on and sketches of crane flies.

Despite their conspicuous presence and flamboyant behavior, I’m unable to determine what species they belong to. But that is not unusual—I have not seen and don’t know about the vast majority of species that live all around us, even the conspicuous ones. And new ones keep coming. In the summer of 2006 I saw for the first time huge flies with striking white faces and lemon yellow bellies. They were feeding on the meadowsweet flowers. I later learned that they were Belvosia bifasciata, a species of tachinid flies that specialize in parasitizing large caterpillars, particularly those of saturniid moths.

There are many insects with “fly” names (such as butterfly, dragonfly, ichneumon fly, and dobson fly), but there is only one group of true flies, the order Diptera (“two wings”). As the name of the order implies, its members are distinguished by having only two wings, rather than four as in all the others. Worldwide there are an estimated 240,000 species of true flies, but only about half have been described (i.e., named). (About 25,000 have so far been described in the United States.) Here in Maine, a group of about half a dozen fly species make up the deficit for most of us, in terms of familiarity. These all-too-intimate cohabitants of our summer world live in a vast geographical area stretching from the New England forests through the Canadian tundra. These animals (mostly mosquitoes, blackflies, midges, deerflies, and horseflies) seek us out in the flesh, rather than vice versa. We wish they would not. Because of their great numbers they are almost always memorable to those who meet them at the often very specific time in the summer that they claim as their ecological niche.

Dipterans attack animals, from caterpillars to caribou, in devious, ingenious, and horrible ways. For example, some eat their victims from the inside out, some from the outside in. But to be fair, the majority of the thousands of species are unobtrusive and can be enchanting. There are some who mimic wasps and colorful furry bumblebees; others have exotic forms that make them seem like aliens from outer space. Some are wildly beautiful, and there are many rare species that none of us will ever get to meet.

Every fly has its place and its season, and many flies have a specific time of day (or night) when they are active. Those that I know most intimately are not as entertaining as the dancing crane flies (there are also hundreds of species of these), who must remain anonymous for now, as I do not know their names. With regard to the next lot, who are familiar in summer, I shall be scarcely more specific and give only generic names.

Mosquitoes, the first on the list of familiar local dipterans, are the least objectionable, because, unlike species in the tropics, the northern species are not carriers of malaria, dengue fever, yellow fever, or other diseases, as far as we know. Female mosquitoes suck blood in order to get enough protein to make a few hundred eggs, which they deposit in water. The aquatic larvae filter-feed on microscopic particles. They breathe air and, swimming by a wiggling motion, they periodically come up for air, which they suck in through a short tube at their hind end. Almost any pool of standing water where there are no fish is alive with these “wigglers” in the summer. Of course at this stage they are no bother to anyone. It is after they eclose (“hatch”) from their floating pupae that they become blood-thirsty fiends. Those we meet tend to be mostly the females; the males fly around in search of flowers for nectar, females for mating, or both.

Because I’m a mostly diurnal animal and like sunny, open vistas, I have never been much bothered by our mosquitoes. Arctic ones are a different matter altogether, as for some reason mosquitoes get fiercer and more numerous the farther north you go. Caribou may become so depleted of blood by millions of teeming mosquitoes that they lose weight even while grazing full-time.

The only animals that consistently prey on mosquitoes are dragonflies, and they have probably been doing so for at least 100 million years. Mosquitoes seem to have habits that are designed to avoid overlapping with these predators. They avoid the sunshine, where dragonflies are most active, but hordes of mosquitoes appeared as soon as I stepped into dense shady woods where there were no dragonflies. That is, wherever and whenever dragonflies were scarce, mosquitoes were abundant.

Dragonflies that fly at dusk can cash in on mosquitoes. I suspect that the dragonflies’ extraordinary eyes developed to keep up with prey trying to escape into the dark. Behavioral adaptations have the same effect. While walking in grass in Botswana during the heat of the day, I saw mosquitoes spring up, and I was then followed by several dragonflies that were hawking them. The dragonflies seemed to be following me directly, because when I shifted to a slow jog they continued to follow me. They were acting like some species of birds—cowbirds in North America and cattle egrets in Africa—which also follow large animals because of the prey these animals flush.

Dragonflies are opportunistic. On the evening of 23 July 2005 at about eight o’clock, the air all the way down from our lawn to the beaver bog was full of huge dragonflies. Hundreds were visible, zigzagging back and forth—fairly low, about ten to fifteen feet above the ground. I had never before seen so many at once. Ten minutes later—the sun was still five degrees above the horizon and the honeybees were still working on the flowers—the dragonflies were suddenly done flying.

Mosquitoes are at times an irritation almost anywhere, to be sure, but by knowing their schedules one can avoid many of them. Mostly, this means staying indoors at night. The mosquitoes who get me while I sleep leave a tiny welt that disappears in a few minutes. Newcomers to the woods, who have not yet paid their “entry fee” to nature, don’t always get off quite so easy. It is not a good idea for bare buttocks to be exposed after dark, especially if one’s immune system has not yet been fine-tuned to receive their attention. Big red welts that itch to distraction are a consequence.

Blackflies fill in, and then some, where mosquitoes leave off. They are any of a number of species of small (about 0.08-inch) hunchback flies with thick stubby legs (all the better for crawling into your hair, and through creases and holes under your clothes), of the genus Simulium. Their larvae are filter-feeders that attach themselves to rocks at the bottom of swiftly flowing streams, often in such numbers that the rocks look coated with black mats of moss—but each “moss” frond is a larva. These larval mats may extend endlessly in a stream, and when the adults emerge half of them are hungry for blood. (The other half will be males who don’t need the protein meal.) The flies are silent—unlike mosquitoes, they emit no hum on their approach—and as soon as one surreptitiously lands, it starts sawing into the flesh. Blackflies drive moose to distraction, and affect some people even more severely. People who live near a wilderness or venture into the woods in “blackfly season” (i.e., summer), even those who have over the years developed an immune response, consider these flies quite a nuisance.

My first memories of Maine blackflies are associated with trout streams at a time when my backwoods mentor, Phil Potter, tried to make a man out of me—and out of his young nephew, Bertie. I don’t recall how well he succeeded with either of us, but I won’t forget our simultaneous entanglements with trout fishing lines and blackflies in the alder bushes where we were wading in cold water, while the part of us above water level was all lathered up with DEET. No matter what, the blackflies always managed to find entry points along the sleeves, collar, hair, fly, nose, mouth, and ears. Especially the ears.

My most memorable incident with blackflies occurred in Ontario. My wife and I, our young daughter, and our dog Foonman were making our annual trip to Maine from California. It was a warm, humid summer day. We stopped off in the woods to let the dog out for a brief romp. He jumped out of the car and headed for the nearest tree to lift his leg, but his pit stop was uncharacteristically brief. He raced back to the car even more eagerly than he had left it, chased by a diffuse black cloud.

The problem for us is that blackflies are diurnal. They are active at about the same time as we are and in the same places where we like to enjoy the summer world—out in the woods, the garden, or the trout stream. Few people who have not experienced blackflies have any idea what they can be like. At least I assume so, because I often hear someone complain bitterly about blackflies where they are practically nil. I think, “What blackflies?” To see real blackflies you need to check out the northern woods on any warm day between 1 May and the second week of July. The rest of the summer is usually relatively free of them.

It is possible to somewhat reduce the flies’ depredation, by knowing their habits. First, unlike mosquitoes, blackflies avoid dark, enclosed spaces. Therefore, they don’t molest you in the house, even if the door is kept open. And timing is crucial; they can be almost totally absent on a clear morning, if it is cool. They are equally reluctant to fly at high temperatures: those above 85°F are the niche claimed by another group of flies, the tabanids.

The tabanids, high-temperature specialists, are large, compact animals with short legs and a fast, quiet flight. They have huge, commonly iridescent green eyes, and some of these are colloquially known as “copperheads.” The group includes deerflies, moose flies, and horseflies. Like blackflies, these do not just pierce your skin; nor do they “bite.” Instead, their mouthparts have a bloodletting tool consisting of two side-by-side scalpels that, working like alternately moving blades of a pair of scissors, cut into the skin. While they are at it, like other bloodsuckers and blood lappers the world over, they also rub it in by simultaneously applying anticoagulant from their spittle. They make the blood flow and keep it flowing so as to lap it up all the more easily. Unlike the blackflies, these large flies—in the case of some species, huge flies—are often conspicuous as they zoom around you, yet they are often very cautious in landing. You anticipate a wallop of a “bite” (an incision) at any second, but the critical and continually anticipated event may be delayed for minutes as they keep circling around your head, waiting for an opening. While I’m running, they fly circles around me, searching for an opening, which is usually under the damp hair on the back of my head.

Of the many biting flies, for me the most objectionable are the smallest: the midges, also called no-see-ums. They are especially active on warm, balmy nights. Not only don’t you see them; you don’t hear or smell them either. But when they arrive, you know it. You feel crawling, burning sensations on all exposed areas of the body, and then also on the unexposed areas. These insects come at you even inside your dwelling, and most window screens are no obstacle to them.

A friend, a guide in Maine, once entertained a couple of summer “sportsmen” from New Jersey who had never encountered midges before. He told me of one memorable incident with them. The party of three arrived at dusk at their bucolic, Edenic campsite deep in the Maine woods. As they were unpacking and getting set up, the sportsmen began to scratch. Then, suddenly realizing that they were under attack, they jumped up and went “literally crazy,” as my friend put it. They eventually ran off into the woods, trying to escape their tormentors. Unlike the superfast tabanids, which not even a deer can outrun, no-see-ums can be outrun by a reasonably fit man. But the problem is that there is no place to run to, because they are everywhere.

Smoke. DEET. Running. Nothing worked to diminish the sportsmen’s pain. Even sooner than anticipated, they resorted to trying to distract themselves with their precious stock of beer. However, the night was hot and muggy and the midge onslaught was long; their beer supply ran short. After that my friend had to spend the night with his guests in their truck, driving back and forth on a bumpy road through the forest to create a cooling breeze that would blow the midges off. It worked, until their gasoline ran low. Drained in more ways than one, the summer vacationers sped back to New Jersey in the morning.

Well, at least in New England nobody has to pay homage to botflies. These are nonbiting flies, but they can be even more bothersome than the blood specialists—especially for caribou in the arctic. The large botflies bother caribou to distraction by flying up their nostrils to deposit, not eggs, but live maggots that will burrow in and wander around in the body before lodging under the skin to grow there to adulthood. When the maggots are well fed and fully grown they pop out of the caribou’s skin to pupate on the ground. In winter, on a freshly skinned caribou hide, I have seen dozens of large white welts, each containing a big botfly maggot. I have also seen botflies on skinned mice and chipmunks in Maine; relative to the size of their hosts, one of these maggots would be as big as a woodchuck to us.

I’ve learned a few things from flies. I’ve learned that it’s unproductive to swat gnats. I’ve learned that it’s a good idea to look at flies carefully, to distinguish the bothersome from the benign. The good ones, for me, are those who dance for their own pleasure. I do not disdain those who suck my blood so that that they can lay their own precious eggs; they are just programmed that way. It’s pointless to try to reason them out of it. It’s better to take hits without flinching, and to develop an immunity to the toxins.

Aside from that, flies give me hope. They also inspire others, as I learned from a bumper sticker that made my day a little over a year ago. It said in bold black letters: “Save the Blackfly.” I trailed behind the car with the sticker for about twenty miles before it finally pulled over in Plainsfield, Vermont. I pulled in right behind. I could now read the fine print at the bottom of the sticker. It said: “Maine Blackfly Breeders Association.” I wanted to belong, knowing that blackflies effectively do more to fulfill the promise of the well-known state slogan to “Keep Maine green” than anything government ever would or could do to keep “development” at bay. But as I walked over to introduce myself to the gentleman in the car, he stepped on the gas pedal and quickly drove off.