Read an Excerpt
Chapter 1
God's Favorite
Human knowledge will be erased from the world's archives before we possess the last word that a gnat has to say to us.
-Jean-Henri Fabre
On about the sixth day, I realized that the four tiny red welts on my chest were not mosquito bites. It was our third week of a month's sojourn in Kruger National Park, South Africa, where I was one of a team of 14 biologists studying the movements and roosting habits of bats. A small group of us were taking a lunch break during a foray on foot to track the locations of several radio-tagged African yellow house bats.
I had noticed that the welts were becoming larger and itchier with each passing day but had shrugged it off, thinking I must be more sensitive to the bites of whatever African mosquito had had its way with me. As I absentmindedly scratched the bumps through my shirt between bites of a sandwich, I felt a strange sensation-a faint tickling. I peeled off my shirt and scrutinized one of the welts.
It was moving.
Years earlier, I had read of large botfly maggots tunneling their way under the skin of the arms and legs of a teenager who had miraculously survived a midair plane explosion en route to Lima in the 1970s. Her earthward plummet was cushioned by vegetation, and she awoke, still strapped into her seat, in the Amazon jungle. Armed with courage, determination, and a knowledge of edible plants she had learned from her botanist parents, she survived a twelve-day solo hike through the bush to civilization.
My infestation was less dramatic. These were not botflies. Back at camp, Leo Braack, our South African park ranger who happened to be an authority on parasitic flies, soon identified my uninvited guests as African skin maggots, Cordylobia anthropophaga. Anthropophaga translates to "man-eater." Drawn to the rank odor of sweaty clothing I had hung up to dry, the mother fly had laid her eggs on the unclean garments, and when I had re-donned them thinking I could get away with a second wearing, the maggots, stirred by my body heat, had emerged to tunnel through my skin. Burrowed headfirst into my flesh, the hungry grubs breathed through a miniscule hole at the surface. My four tiny wounds were painless, but itchy.
I should say that while the label man-eater is technically true, this was not the sort of consumption that has given certain sharks and tigers their ill-deserved reputations. I wasn't about to lose a limb or spill blood. Nevertheless, it is disconcerting to discover another creature gnawing away at your flesh, however small. Suddenly, my own lunch was displaced by a new priority concerning someone else's: I wanted them out!
An hour later, while I posed for photos at our campsite along the Luvuvhu River, Braack instructed me on how to remove the maggots:
"Just rub a little Vaseline over the opening, and you'll be able to squeeze them out in about 30 minutes."
"That's comforting," I thought. "Easy for you to say."
I retired to a shady spot with a tube of Vaseline and a good book. An hour later I had expressed three pearly-white, rice-grain-size maggots. The fourth one held out until the next day.
Not only was I the only human on the trip to host African skin maggots, but I was at that time the only person in history to host them at our location, according to a delighted Braack. Common though they are, African skin maggots had not been recorded that far south on the African continent. I was soon being lovingly referred to as "the ecosystem" by my comrades, and I became the butt of hygiene humor for the remainder of the trip. Apparently, none of them caught the irony that I, the only vegetarian in the whole group, should be the one whose flesh was deemed most suitable for consumption by a fly.
Unpopular and Important
Let's face it, flies do not win popularity contests with us. Among our most feared animals, flies are vastly outranked by the likes of spiders, snakes, lions, and crocodiles. But if one were to survey humankind for animals we most dislike, flies would make many top-ten lists. "Of all the major groups of insects, the flies are the least understood and most detested," writes entomologist Mark Deyrup in his 1999 book, Florida's Fabulous Insects. "There are no apologists for flies, there are no lobbyists or hobbyists for flies, there are no fly-watchers, no fly-gardens, no picture guides to flies." (Deyrup's last claim has been rendered obsolete, as we'll soon see.) For sheer repugnance to humans, an adult fly is surely trumped by its fellow insect the cockroach, but a juicy fly maggot propelling itself across the putrid flesh of a rotting carcass with successive undulations of its viscera visible through translucent skin makes for stiff competition on the yuck scale.
Then there is their dastardly lust for blood. While most of us go through life without playing host to a flesh-eating maggot, it is a rare human who has not suffered the unsettling whine of a mosquito or felt the familiar itch of her bite. Chances are that anyone reading this will also have been harassed by blackflies, sand flies, deerflies, stable flies, and/or horseflies. Having spent thousands of hours exploring the North American outdoors, I have been targeted by all of these aerial phlebotomists. The business end of a large horsefly has a set of mouthparts that work like alternating saws to penetrate the skin, and the pain is nothing to scoff at. I was terrified by my first encounter with one while swimming at an Ontario summer camp as a young boy. The big black creature swooped down onto the heads of swimmers when they surfaced. The pain of its bite was immediate and severe. I desperately wanted to turn into a fish. I once saw a large horsefly gorging on the flank of a cow in Texas hill country, blood dripping copiously from the wound.
If painful bites were the only cost of cohabiting this planet with dipterans, we'd have it good. Flies wreak far greater havoc as vectors of deadly tropical diseases unwittingly delivered to humans and other animals through their bites. Half of all clinical cases of disease in the world are transmitted by insects, and flies are the most common carriers. A human dies of malaria every 12 seconds, and mosquitoes of various species are its primary couriers. Not ones to retreat from mayhem, mosquitoes also deliver the microbes for yellow fever, dengue, Zika, filariasis, and encephalitis.
Mosquitoes are not the only culprits. Tropical sand flies spread leishmaniasis in humans, and tropical blackflies can carry the roundworm that causes river blindness. One in six humans alive today is infected by an insect-borne illness, and more often than not, the footprint left at the crime scene is that of a fly.
I am not writing this book to demonize flies. I have no personal grudge against them. Only a tiny proportion, about 1 percent, of the 160,000 known species of flies are harmful to humans. By contrast, the beneficial and pretty flower flies (Syrphidae) alone, which are vital pollinators, number over 6,000 described species. Our common antipathy toward insects in general, and flies in particular, obscures a range of critical beneficial services they perform, including pollination, waste removal, natural pest control, and being a critical food source for scores of other animals. Few of us are aware of these and other fly benefits. For instance, you probably didn't know (I didn't) that midge larvae around the world are an important antipollution brigade; in their multitudes-billions per acre in some locales-they filter algae and microscopic debris from the water, which they draw in a little stream through an open-ended tube they build around themselves, facedown in the mud. Even the devilish bites of certain flies have hidden benefits-that is, if you don't adhere too closely to anthropocentrism. Biting flies have kept humans out of ecologically sensitive areas, preventing habitat and biodiversity loss. Case in point: the lush Okavango Delta of Botswana-a seasonal floodplain spanning some 16,800 square kilometers (6,500 square miles)-is a paradise for wildlife and a stronghold of the tsetse fly, whose bite can sicken both humans and their cattle.
Flies also play major roles in science. Modern genetics owes much to the fruit fly, Drosophila melanogaster, which has been the subject of over a hundred thousand published studies. And crime solving owes a debt to Diptera. Such is the speed and efficiency with which certain flies colonize our dead bodies that entomologists, armed with an intimate knowledge of the life history of these fly species, can determine time of death to within a few hours. This technique has aided hundreds of murder convictions, and exonerations.
Megadiverse
Useful or not, flies are hugely successful. I did not choose the subtitle of this book lightly, nor am I hedging with the claim that they rank as "God's favorite."
What do I mean by the success of flies? That adjective seems hardly apt for an imprisoned housefly bouncing inanely against a windowpane. What I am actually referring to is a more biological sort of success: diversity and sheer numbers. On these terms, flies' success takes on celestial proportions.
First off, flies belong to by far the most successful collection of animals on Earth: insects. "It is easy to forget that human beings form a tiny two-legged minority in an overwhelmingly six-legged world," writes Canadian entomologist Stephen Marshall in the introduction to his 2006 book, Insects. Insects make up a whopping 80 percent of the approximately 1.5 million animal species so far named, and there are estimated to be between 5 and 10 million species yet to be discovered. At any one time, there are some ten quintillion (10,000,000,000,000,000,000) insects crawling, hopping, burrowing, boring, or flying. That's 200 million for every living human, according to Animal Life Encyclopedia author Bernhard Grzimek. In his 2017 book Bugged, journalist David MacNeal presents an even more skewed scoresheet: 1.4 billion insects for every human. Ants alone are thought to outweigh humans twelve times over, and Lisa Margonelli reports in her book Underbug that termites outweigh us by a similar ratio. A typical backyard may contain several thousand species of insects and several million individuals.
Nobody knows how many living flies there are on planet Earth at any one time, but researchers at the Animalist channel think there are about 17 quadrillion (17,000,000,000,000,000). British fly expert Erica McAlister estimates there are about 17 million flies for every human. With numbers like these, you may rightly wonder why we are not constantly mobbed by clouds of pesky gnats, mosquitoes, and crane flies. The reason is that most flies are in preadult stages (eggs, larvae, or pupae) and thus lack the conspicuous characteristic they are named for. Nonetheless, such is the abundance and ubiquity of flies that, as you read this, you're likely within a few feet, if not a few inches, of some sort of fly. Wherever you are in the world, if the weather is warm and you spend time outdoors, you will almost certainly be in physical contact with at least one fly on any given day.
You may be excused for doubting the above numbers. It is hardly as though the air and the ground are swarming with insects. But there are vast expanses of land, particularly in far northern latitudes, where insects at their reproductive peak, and flies especially, really do swarm in prodigious number. The Russian translator of one of my books sent me links to videos of tens of thousands of horseflies and blackflies swarming on and around an all-terrain vehicle in a Siberian wetland. The videographers are well protected in netting and gloves, but I shudder for any reindeer who treads there. Then there are the midges, which might turn out to be the most dominant collection of species on Earth. Phil Townsend, a remote-sensing specialist at the University of Wisconsin in Madison, reported in 2008 the laying down of 135 kilograms of dead midges per hectare (120 pounds per acre) per day around Iceland's Lake Mvatn (English translation: Midge Lake). Some phantom midges amass in such huge numbers in East Africa that locals catch them in swinging buckets, then pack them into balls and cook them into edible masses called kungu cakes.
For the record, I'm not suggesting that any kind of fly is the most abundant species on Earth. As we go to smaller organisms, some of their numbers rise astronomically. There are more living organisms in a single teaspoon of healthy soil than there are people on Earth. One of the most abundant animals on the planet is a well-studied nematode (roundworm) called Coenorhabditis elegans. A British biologist estimated that 600 quintillion of them are born every day. According to a 1998 estimate, there are about 510 bacteria on this planet.
Another measure of evolutionary success is number of species. Depending on which expert you ask, flies may rank first, second, or third (after beetles and maybe wasps/ants/bees) as the most species-rich order of animals on Earth. In the 1930s, British geneticist J. B. S. Haldane famously said that God had "an inordinate fondness for beetles," owing to beetles' fantastic diversity, which at that time far outranked that of flies. Today there are about one million known species of insects, of which 350,000 are beetles. But most flies are generally more elusive and obscure than most beetles, and as scientists have redoubled their efforts and honed their skills at collecting and identifying new species, flies have been catching up.
There were about 80,000 known species when Harold Oldroyd's classic book The Natural History of Flies was published in 1964. That number has since doubled to 160,000, and there are signs that we are still only scratching the surface. A DNA barcoding study from 2016 estimated the diversity of gall midges in Canada to exceed 16,000 species-10 times the predicted number. Extrapolating this finding leads to a startling prediction: "If Canada possesses about 1 percent of the global fauna, as it does for known taxa, the results of this study suggest the presence of 10 million insect species with about 1.8 million of these taxa in the gall midge family Cecidomyiidae. If so, the global species count for this fly family could exceed the combined total for all 142 beetle families." Haldane must be rolling in his grave. According to one fly specialist I spoke to, there may be some exaggeration in this extrapolation, but clearly they are "a huge, huge group," nearly entirely undescribed and mostly plant-feeders. At present there are only 6,203 named species of gall midge worldwide.
Steve Marshall is unambiguous in his appraisal of flies' place at the top of the diversity heap. I met Marshall on the suburban campus of the University of Guelph, about an hour's drive west of Toronto, where for 35 years he has served on the environmental biology faculty and as director of the university's world-renowned insect collection. During that time he has built an impressive résumé that includes well over 200 scholarly publications and several magnificent volumes on insect life illustrated with thousands of his own arresting macrophotographs. Alongside Art Borkent (whom we'll meet later), Marshall is Canada's fly guy.
