Houseflies as Health Hazards

Environmental and medical historians know a good deal about the spread of diarrheal pathogens and their relation to the niche of Musca domestica. Female houseflies lay their eggs (usually anywhere from 100 to 150) in horse manure, refuse, or other rotting organic matter. Horse manure in particular provided the flies with a “near-perfect medium” for breeding and feeding, and it also often contained bacterial (like salmonellosis) and parasitic (like cryptosporidiosis) pathogens that were among the likely causal agents for “summer diarrhea.”3Webb, The Guts of the Matter, 75. Female flies try to find warm organic matter, rotting in sunlight, in which to bury their eggs, where they incubate for anywhere from eight hours to two days before the larvae hatch to feast upon the dung.4Harper, Plagues upon the Earth, 137.

Until the first decades of the twentieth century, when horse-drawn carts began to be gradually replaced by automobiles (Britain’s horse population peaked in 1902), the removal of both human and animal (especially horse) waste remained an “imperfect practice” in large British cities, creating an ideal ecological niche for flies to breed and spread diarrheal pathogens.5Hardy, “Death and the Environment in London,” 72–73; Hardy, Salmonella Infections, 69. Hot and dry summers exacerbated the dangers of diarrhea by accelerating the life cycle of the fly (to as short as eight to eleven days) as well as the process of organic putrefaction.6Buchanan, “Infant Feeding, Sanitation and Diarrhea in Colliery Communities,” 161. Historian Chris Otter graphically argues that the English urban environment remained a catalyst for “waves of diarrhea, while large urban horse populations and ramshackle sanitary contraptions provided copious quantities of available dung for larval [flies’] development.”7Otter, Diet for a Large Planet, 186. Neighborhoods still reliant on privies and ash pits, from which waste was irregularly removed, provided flies with “ample access to human excreta” in which to thrive.8Hardy, Salmonella Infections, 69. Dry weather aided the houseflies’ ability to spread pathogens, as it increased the mobility of the flies.9Buchanan, “Infant Feeding, Sanitation and Diarrhea in Colliery Communities,” 161. After taking refuge in the refuse, historian Naomi Rogers argues, flies often “bathed” in coffee, tea, or milk, leaving behind a “trail of filth and bacteria” that ranged from typhoid to dysentery to infantile diarrhea.10Rogers, “Germs with Legs,” 599, 606; Biehler, Pests in the City, 30–31. Flies infrequently came into direct contact with children, but, they exposed the child to diarrheal pathogens by way of the syrup, milk, bread, or fruit that the flies visited in a shop or home.11Niven, “Summer Diarrhea and Enteric Fever,” 158. Sweetness and sugar are as much a treat for flies as they are for humans, which flies can detect with special taste organs on their feet.12Connor, Fly, 54. The working-class kitchen, Otter argues, was a bountiful feeding ground for flies, “enticingly splattered with sugar and condensed milk.” While they feasted, flies spread infectious material around as they “manically vomited and defecated assorted microorganisms” onto foodstuffs and serving implements or, more dangerously, the baby’s milk supply or bottle.13Otter, Diet for a Large Planet, 186.

Contemporaries at the turn of the twentieth century were also actively studying fly ecologies, and warned housekeepers of the importance of guarding the “home from the housefly.”14Rogers, “Germs with Legs,” 601; for an example of a study conducted in the city of Liverpool, see Newstead, “Preliminary Report on the Habits, Life-cycle and Breeding Places of the Common House Fly,” 506–22. Books like Charles Gordon Hewitt’s House Flies and How They Spread Disease, published in the Cambridge Manuals of Science and Literature series in 1912, sought to educate the public on the dangers of the housefly. Hewitt, a Canadian entomologist, argued that flies carried organisms in their guts and then, through defecation or vomit, discharged these onto human foodstuffs on which they landed and fed.15Hewitt, House Flies and How They Spread Disease, 73. Hewitt explained how human excrement in latrines or ash pits, as well as other forms of waste, created favorable conditions for flies to breed and lay their eggs. He further argued that houseflies required warm temperature (25 to 30°C) to lay their eggs, resulting most frequently in breeding beginning in the early summer and egg-laying during the hottest months, typically August and September.16Hewitt, House Flies and How They Spread Disease, 20, 27. Thus, the connection between climatic conditions, especially summer temperature and rainfall, and cases of diarrhea each year becomes clearer. In hot, dry summers, when subsurface soil was less frequently cleansed by rainfall, this resulted in a greater accumulation of refuse, which then created an ecological niche favorable for fly breeding and egg laying. A surge in cases of summer diarrhea often followed when the fly populations took flight, which explains why the highest number cases tended to occur in the late summer and early fall.17Hawes, “The Development of Municipal Infant Welfare Services in St Helens,” 167.

By the turn of the twentieth century, the Medical Officers of Health clearly understood the danger that houseflies posed to both public health and children’s health.18Hardy, “Food, Hygiene, and the Laboratory,” 299; Wall, Bacteria in Britain, 152–53. In 1903, Arthur Newsholme, then Medical Officer of Health for Brighton, who would later become the Chief Medical Officer for the Local Government Board, vividly described how flies spread diarrhea-causing pathogens in the housing of the urban poor. He described housing that had “no pantries; food is stored in cupboards in a living room or bedroom. The sugar used in sweetening the baby’s milk is often black with flies, which have come from a neighbouring privy or manure-heap, or even from the liquid stools of a diarrhoeal patient in a neighboring house.” Despite this, expensive milk supplies were still used. In some impoverished households, Newsholme recalled that “flies have to be picked out of the half-empty can of condensed milk, before its remaining contents can be used for the next meal of the infant.”19Newsholme, “Remarks on the Causation of Epidemic Diarrhea,” 40.

In Manchester, James Niven observed a seasonal pattern from year to year during his tenure as Medical Officer of Health that directly related to the life cycle of flies. In his 1903 annual report, Niven noted: “warm weather brings flies, and warm weather brings Diarrhoea about the same time. It is certain that flies can and do carry infective matters, and the large numbers of flies which settle on food in poor households might, therefore, quite well act as carriers. In cold summers, when there is very little Diarrhoea, there are few or no flies.”20Niven, Report on the Health of City of Manchester, 1903, 167. Relatedly, Niven observed that mortality rates “remained at a uniform low level” from January until late summer, rose rapidly during the three summer months of “fly season,” and then declined “with nearly equal rapidity” in the following months.21Niven, “Discussion on the Etiology and Prevention of Summer Diarrhoea,” 606. He took experimental steps to prove the relationship.

Niven rejected several of the contemporary etiological explanations of summer diarrhea – that it grew in the soil, that it was carried in fruit, or that it was simply caused by dust. In his study he questioned how the bacilli could escape from the soil in well-paved central districts (Ancoats, Bradford, Central, Clayton, St. Georges, West Gorton) and yet not be prevalent in “the comparatively uncovered parts of outlying districts” where the wealthier classes lived, and diarrhea was less prevalent. With regards to fruit, he questioned how the appearance of the disease occurred in house after house in which “the infant has no fruit”. To Niven, the seasonality of the disease challenged the dust explanation. He asked, “why should dust effect so much in August, so little in March, April, May, June and July?” His answer to all these questions was the role of the housefly. He argued that in the poorer central districts, collections of horse manure and other organic waste created the favorable ecology for the flies to breed; rotting fruit attracted flies to the sugar and the seasonality coincided with the breeding season of the housefly in the late summer. This then caused the higher rates of diarrheal mortality in the central districts.22Niven, “Summer Diarrhea and Enteric Fever,” 134–40.

To prove his theory, Niven began a careful study of the role of the housefly in connection with the spread of summer diarrhea in 1903. He asked households to track, day by day, the number of houseflies they caught in a bell-shaped glass trap which he provided to them. These traps were “covered above but accessible from beneath, the lower rim curving inwards to form a semicircular ring, into which was to be poured day by day a thin sweet beer . . . very attractive to flies; they enter from below, hasten to partake of the beverage, and get drowned.”23Niven, “Summer Diarrhea and Enteric Fever,” 141. The number of flies was then compared with the rate of diarrheal mortality in that district. Niven continued this study annually until 1909. He published the results of this years-long study in the Proceedings of the Royal Society in 1910, reporting that the highest diarrhea mortality rates occurred in the poorest, more densely populated, urban districts.24Niven, “Summer Diarrhea and Enteric Fever,” 134, 168–69.

Based on the results of his observational study, Niven came to several important conclusions about the nature of summer diarrhea and the role of flies as its vector. First, he discovered that there was a lag between the onset of the illness and death (slightly longer than one week), and that this lag grew longer over the course of fly season. Second, unsurprisingly, he found an apparent correlation between a sudden rise in temperature, which he argued enabled the breeding of more flies, and a surge in diarrheal mortality. Third, he found that “deaths diminish more rapidly than do flies” in the latter part of the season. For this he had two explanations: one which related to the children and one that resulted from the life cycle of the flies themselves. “In years of high [mortality] the more susceptible and exposed infants have been killed off or rendered immune [earlier]. In every year towards the close of the fly season the flies are attacked by Empusa muscae [a fungus fatal to flies] and are hindered by the cold from leaving the house, so they cease to act as transmitting agents.”25Niven, “Summer Diarrhea and Enteric Fever,” 145, 153–54.

So, why do flies matter? The housefly became an important bridge between the environmental and social conditions that created a serious threat to children’s health. While seasonal environmental conditions created a favorable or unfavorable niche for flies to breed, flies also needed to enter and contaminate the household to endanger children’s health. The hygienic conditions of English working-class homes intensified or lessened the risks by attracting flies. The local Medical Officers of Health certainly were aware of these problems, as we saw in Newsholme’s vivid description of a working-class home. Convinced that flies were a major vector by which summer diarrhea spread, Medical Officers of Health like James Niven became increasingly convinced that protecting children’s foodstuffs from contamination by flies was the key to preventing the spread of summer diarrhea. To save a baby from the threat of diarrhea required the elimination of detritus in and around the home. Enhanced city-wide sanitation was an important first step, but, ultimately, macro-scale interventions alone were insufficient to mitigate the dangers of diarrhea. Niven believed that reforms also had to improve the hygienic conditions and ecology of the British home. As interventions became much more intimate, and, perhaps, as Mooney argues, more “intrusive,” this invites us to think about the second and third stages of my argument. Efforts to defeat diarrhea in the household required further public health interventions in the last decades of the nineteenth century (well before Niven’s study was even finished). In so doing the state began to intervene much more deeply into the private lives of English parents and their children.26Mooney, Intrusive Interventions.