IN A MEMORABLE CARTOON from my formative years, a well-dressed man with a goatee is seated at a restaurant table across from a fly. It’s a giant fly, a fly large enough to fill a dining room chair much the way a person would. The man addresses a waiter. I’m paraphrasing here. “I’ll have the gazpacho, and some shit for my fly.” It was a commentary on flies, or perhaps an observation on the odd human habit of elevating nutrient intake to social ritual. Or maybe just this: No matter how fond you are of a fly, dining out together is going to be awkward.
And the cartoonist only drew the half of it. Because flies have no teeth, they must first liquefy what they plan to eat. (Or order the gazpacho.) This they do by applying their digestive enzymes outside their body. The process was captured on film and included in the 1940s British Army hygiene filmstrip The Housefly. “Their vomit is puddled about your food to make a kind of porridge,” says an incongruously posh-sounding narrator, “which the fly then sucks up.” Technical Guide No. 30 (Filth Flies) of the US Armed Forces Pest Management Board would also have you know that “flies further contaminate food by defecating on it while they feed.”
No flies of any size are eating at Mi Rancho Mexican restaurant in downtown Silver Spring this evening, but some fly biologists are here, and that can be equally disquieting. We’re talking now about those out-of-body digestive enzymes. A researcher I had spoken to the previous week referred to the salivary glands, not the stomach, as the source. For clarification, I have turned to one of my dinner companions, George Peck, resident filth fly expert at the Entomology Branch of the Walter Reed Army Institute of Research (WRAIR), just down the road.
“I think it’s both,” Peck is saying. “They vomit up enzymes from the crop along with the saliva and let it—”
“Are you all done here?”
Peck looks up to acknowledge our waitress. “I am, thanks . . . and let it fall onto the food.”
With George Peck, the topic of flies and their unusual physiology doesn’t elicit disgust. Awe, mostly. I have heard him marvel at the sensitivity of the fly’s body hairs, how they enable it to detect the bow wave of an approaching hand and lift off in the split second before contact is made. He talks about the halteres, tiny gyroscopes that enable the fly to hover or change direction “faster than the fastest flight computer on any jet.”
Less awesome: Researchers in Japan established that the strain of E. coli known as 0157:H7—deadly outbreaks of which periodically make headlines in the United States—thrives in housefly mouthparts and frass.* Bacteria on or in filth flies have been shown to transmit typhoid fever, cholera, dysentery, and a whole wet bar of lesser diarrheal infections. (Both houseflies and blowflies fall under the grouping “filth flies.”) British researchers documented a close association between filth fly populations and cases of food poisoning from the campylobacter bacterium, both of which peak during the warmest months. (The English used to speak of “summer diarrhea”—loose stools and cramping having joined warm nights and fireflies as hallmarks of the season.) In a 1991 study, an Israeli military field unit that undertook an intensive filth fly control program saw 85 percent fewer cases of food poisoning than a similar one that did not.
The Armed Forces Pest Management Board’s filth fly technical guide includes a figure for the number of times in twenty-four hours that a single fly vomits and defecates on its food after a controlled feeding of milk. The figure, a range from 16 to 31, was arrived at not by staying up all night watching but by counting “fecal spots” and “vomit spots” (the latter distinguishable from the former by their lighter color). The reader is invited to speculate about the number of “spots” on food in a military chow line in the era before sealed dining facilities. Fly infestation in the mess halls of the Vietnam War, the guide relates, was so intense that “it was difficult to eat without ingesting one or two . . .”
Infestations still happen, mostly in the rough and not entirely ready first few days or weeks of a war. Early on, weapons and ammo take priority over latrines and refrigeration units in terms of what supplies get shipped. During the first Gulf war, Marines arrived in the region via the port of Jubail, where the Saudis housed them in a warehouse. “We had ten thousand Marines and two squat toilets,” recalls Joe Conlon, a retired Navy entomologist. The toilets soon clogged and sewage ran in the streets. Meanwhile, with no refrigerated storage, pallets of produce began piling up on the dock in the 100-degree heat. Thousands of flies converged. Conlon estimates 60 percent of the Marines got sick.
Historically, battlefields were even worse. Combat is a filth fly cornucopia—a bounty of rotting organic matter to eat, to lay eggs in, to nourish the offspring. On Pacific islands during World War II, says the Armed Forces Pest Management Board guide, “flies developed in corpses on battlefields and excrement in latrines to levels beyond modern comprehension.” A similar scenario developed in the aftermath of battle in El Alamein, Egypt, prompting officers of the British Eighth Army to mandate fly death quotas—each soldier responsible for killing at least fifty flies a day. During the Vietnam War, corpses became so heavily infested with maggots that pesticides had to be used inside body bags.? In Conlon’s camp on the Kuwait border, accumulating garbage exacerbated the problem. The Marines weren’t allowed to burn it—the normal disposal strategy—because the fires would give away the camp’s position. (The garbage eventually became part of military strategy. It was hauled away under cover of darkness and burned at a distant site, to trick the Iraqis.)
Nowhere was the filth fly situation more dire—or perhaps just more memorably documented—than in the American Civil War. “Few recruits bothered to use the slit trench latrines . . . ,” wrote Stewart Marshall Brooks, in Civil War Medicine. “Garbage was everywhere . . . [alongside] the emanations of slaughtered cattle and kitchen offal.” Entomologists Gary Miller and Peter Adler, in a paper on insects and the Civil War, quote a letter by an Indiana infantryman describing the scene: “The deluge of rain which had fallen . . . soaked the ground until the whole face of the earth was a reeking sea of carrion. . . . Countless thousands of green flies . . . were constantly depositing their eggs . . . which the broiling sun soon hatched into millions of maggots, which wiggled until the leaves and grass on the ground moved and wiggled too.”
You can imagine what might happen to the open wounds of a soldier lying on a battlefield for any length of time. Most likely you would be wrong.
THE SOLDIERS, two of them, are not named, nor is the battlefield on which they were hit. We know that it happened in France during World War I, sometime in 1917. We know that it wasn’t winter, because the men arrived at an army hospital having lain “in the brush” for seven days. And because it was fly season.