Shoo Fly

My summer vacations have always been spent hiking in the north woods of Michigan. Both the days and Lake Superior’s waters are crisp and clear, and the only fly in the ointment are literally the flies that occasionally arrive in hordes. Horse flies are generally a minor annoyance, since they do not arrive in droves, but occasionally one will relentlessly circle your head for hours on end. Their endless droning can drive you to distraction, and then when the droning stops, like a landed grenade, you may have mere seconds to avoid the incoming bite. My strategy is to constantly swing a branch over my head, in the hopes of nudging a horse fly into another orbit around an adjacent hiker. Perhaps this is a breach of trail etiquette; once you acquire a horse fly, maybe it should be yours until death do you part, but personally, I am very satisfied when my in the midst of my wild swinging, my stick lands a glancing blow to the horse fly, and then suddenly I hear a fellow hiker curse as the fly assumes a new orbit.

It is the beach fly that can be the scourge of an August vacation. They predictably arrive with a south wind, and within hours of a wind change, it seems that the beach is inundated with flies in plague-like proportions, coating people and dogs, following both inside and into the dining hall with unappetizing results. The first hint of the descending horde might be the gathering number of flies noted on the person walking ahead of you, and then the growing realization that your back is probably covered as well. I remember one memorable hike where I looked down on my pant leg and was struck dumb by a patch about the size of the palm of my hand that was covered with a seething orgiastic mass of flies. Perhaps they were whipped into a frenzy by an inadvertent smear of mayonnaise on my pants, perhaps this was some sort of breeding ritual, but this incident has left a searing memory as something truly revolting, and also left me with the knowledge that you cannot outrun flies.

Flies are also challenging since, unlike mosquitoes, they are difficult to catch and kill. I remember sometime in my teenage years, someone came up with the more successful alternative to merely trying to swat the fly, but instead actually clapping right above the fly. Apparently those huge complex eyes could detect the swat but not the clap. I also recall a few memorable summers where one of my peers had developed sufficient hand eye coordination that he/she could actually snatch a fly from off a pant leg, then shake it madly in the fist, finally slamming the disoriented fly onto the table or ground. If that weren’t enough, you could then pluck a hair from your head and tie it onto the fly’s thorax. When the fly came to, it would fly around, tethered on the world’s smallest leash, to the great amusement of all.

I also remember the now bygone tactic of flypaper, that gooey yellowish strip of paper that you could hang in critical areas, watch as the flies slowly accumulated over your head or in the kitchen, and then discard when the fly paper was completely filled, or you were totally grossed out, whichever came first. My mother used to hand out the flypaper to each of us siblings with the challenge to find the best place to hang it. Whoever had the most flies on their strip of paper, would win. Yes, we Browns were a competitive family.

A few summers ago when the south wind blew, I tried to approach the beach fly issue more intellectually. Really, where did all these flies come from, and why did they appear so reliably with a south wind? Could they really have been blown all the way here and why were they dumped on the beach? It seemed odd that they could truly have been blown there, because the interior woods were relatively still, and the simple fact that there were so many of them in such a short period of time. Throwing many years of higher education at this problem, I came up with three possible theories; 1. either they were blown there; 2. they were born there during the hot dry weather, or; 3. the flies were always there, but just became more active during the warm weather. My theorizing came just at the time that Edie Farwell was planning her nature school in the fall and was looking for guest lecturers. I volunteered to give a lecture, figuring that this would give me the incentive to research the possibilities.

It turns out that the term “flies” refers to the general insect order of “Diptera,” which includes some 120,000 species; in fact 1 in every 10 animals is some type of fly. For example, a mosquito is technically a fly. Diptera are unified by the presence of a paired set of wings, and a life cycle involving a soft wingless larval stage transforming to a hardened winged stage. Some of you may be recalling the sadistic moments in your childhood when you pulled wings off flies, and are thinking, hey I only remember two wings, where’s the other set?” Well, the hindwings of flies are reduced to mere nubbins and are called “halteres.” The halteres function as balancing organs during flight and are responsible for the acrobatic movements of flies. The focus of my nature lecture to Edie’s class was a search for the halteres with a magnifying glass. If that failed, I was going to show the kids how to immolate flies with focused light. I think we spotted the halters so the flies escaped a fiery death.

I was overcome with sheer number of different kinds of flies, but it seemed most likely that the beach flies were either house flies (Musca domestica), cluster flies ( Pollenia rudis ), or stable flies (Stomoxys calcitrans). House flies don’t bite since their spongy mouth parts only allow them to ingest liquids, cluster flies crawl through small openings into a house, but the stable fly seemed to fit the bill. The stable fly breeds in the fetid and fecund environment of rotting vegetation (common along ocean beaches) or a mixture of manure, urine and straw. Stable flies can have a big impact on the diary and cattle industry, since harassed animals either grow slowly or do not produce as much milk; this economic impact has fueled most of the research. Many variants of fly paper and traps are common around stables; one website even recommended outfitting cows in a pair of old trousers for protection. I have never been clear about the distinction between trousers and pants, but would intuitively agree that trousers would be a better choice for a cow.

A literature search on the scientific name Stomoxys calcitrans revealed that there is considerable research interest in why flies accumulate along the beach. In particular I discovered several articles specifically on the beach fly problem around the Great Lakes and its impact on the tourist industry. Dr. Carl Jones and Dr. Jerry Hogstette were authors on several of them and both were gracious enough to spend some time with me on the phone. The technical description of their research is a combination of aerobiology (the dispersal of organisms in the air) and phenology (the study of the relation between biologic phenomenon and climatic change), and Dr. Jones admitted that research money to solve the problems of beach tourists has dried up a bit since 9/11; money for aerobiology research is now focused on more on terrorist tactics. The most prevalent theory of fly dispersal still focuses on weather patterns. Dr. Hogstette hypothesized that young adults (< 2 days old) are the most sensitive to changes in barometric pressure which prompts them to fly up where they caught up in the moving air above the tree tops where they are blown along. Swarms of flies have been spotting at up to 18-25,000 feet, moving along at 18-25 miles per hour. The next step is to flush the flies out of the air current. Competing weather fronts often collide over large bodies of water, and air may be very still at their juncture, allowing the flies to drop down through the cracks, so to speak. There are anecdotes of fishing boats, some 60 to 70 miles off shore, that will suddenly have a cloud of flies rain down upon them.

While the theory made intuitive sense, it didn’t explain why the flies always seem to drop in right along the beach, and often at a time when the sky is cloudless and there is no hint of a colliding weather front. Dr. Hogstette explained that the flies could be dropping out over a broader area over the water, but are sucked back along the beach due to the air rising over the hot sand, creating a vacuum. Furthermore, flies appear to be attracted to water, perhaps due to the distinctive UV light patterns, or the contrast of a sandy beach with the dark water. Dr. Hogstette provided the fascinating detail that these stable flies actually had their origins in Africa, and thus are invasive species arriving in this country around the 1850s. Perhaps they are still responding to environmental cues that were appropriate for their African habitat, but are inappropriate for Lake Superior. Dr. Hogstette would like to study stable flies in their natural environment, but the research dollars in Africa are naturally targeted to the more lethal tsetse fly.

There are still many unknowns, in part due to the technical difficulties of dispersal research. Either you can release tagged laboratory raised flies and hope to recapture them at the target site, or you can catch random flies and hope to ID their environment of origin. Critics of laboratory flies point out that these coddled flies are not hardened to the savage natural world, and thus may behave differently, while the identification of the random flies poses technical difficulties. Dr. Jones has experimented with identifying the pollen clinging to the fly as one technique, but one that requires painstaking microscopic examination of each fly. By identifying pollen patterns, one might be able to match it up with known pollen patterns in other parts of the state, and from this one might be able to determine how long the flies had been airborne.

I was also able to contact Dr. Jim Silek who works at the Public Health Entomology Research and EducationCenter in Panama City, Florida. In Florida they actually spray the beaches if the flies become too dense. The trigger for spraying is a landing rate of 5 flies per minute, which is simply tested by sending someone outside and counting the number of flies that land in a minute. When I mentioned that I have personally experienced a landing rate of probably 100 per minute, Dr. Silek was extremely impressed, “Wow that’s a lot.””

Dr. Silek’s research focuses on control measures that the individual owner might use. His article was intriguingly titled, “Attractiveness of Beach Ball Decoys to Adult Stable Flies.” In this article he tested different colored beach balls covered with an adhesive substance, i.e. essentially big, round globs of flypaper. When the ball is completely covered with adherent flies, it can be popped and placed in a garbage bag for disposal. Alternatively he suggested that outdated political lawn signs could be covered with goo and repurposed as fly trap. Dr. Silek kindly sent me reprints of his articles and also how to purchase the adhesive. (Tangle Trap Insect Trap Coating, Grand Rapids, MI Tel: 616-459-4139). He said that coated beach balls could be hung from a tree or pole at eye height around the perimeter of the property. When I asked how many beach balls I might need, he suggest one every 20 to 25 feet (!) or so. I didn’t have the heart to tell him that the beach in question was about 3 miles long.

Several of my interviewees told me that the flies on the beach issue is a particular problem for Lake Superior, the coastal part of New Jersey, several lakes in the Tennessee Valley Authority, and the beaches of northwest Florida. In particular PorcupineState Park in the western UP has been closed due to intolerable flies. I had originally thought that beach flies were probably endemic at most beaches, but no. Several years ago I wrote another essay on snapping turtles that had as its theme my quest to rationalize my innate loathing of snapping turtles. While not the initial intent of this piece, I now can also begin to appreciate our flies on our beaches. Stay with me, since this will be a hard sell, but the flies on the beach represent another of nature’s clever puzzles that is peculiar to our environment. The stable fly represents an intricate combination of weather, instinct, and a little bit of intelligence, and the conundrum of its behavior has stimulated the human mind to study pollen on the legs of a fly, put sticky goo on old lawn signs and trousers on cows.