In Gaichu no Tanjo (Birth of Harmful Insects), I argued how modern nation building has changed the relationship between humans and nature. Before the early Meiji period, most farmers considered insect outbreaks uncontrollable natural disasters. However, in the 1890s, the government enacted a law forcing farmers to eliminate pests from their paddies. Entomologists also worked strenuously to educate farmers on ways to control insects using scientific knowledge. As a result, the concept of gaichu (i.e. all harmful insects should be controlled by humans) became popular.

This concept expanded to include flies and mosquitoes, which transmitted many diseases in the 1920s. An outbreak of typhoid fever, one of diseases transmitted by flies, became a serious problem in metropolitan areas at the time. As a result, the Tokyo city government began hae tori de (Swat the Fly Day) to mobilize citizens to exterminate flies. Medical entomologists had also begun to play a crucial role in educating citizens about the harmful nature of flies. In these ways, science and politics have changed the relationship between humans and flies significantly.

In this presentation, however, I revisit my thesis and argue from a different perspective by suggesting that Swat the Fly Day was a result of the ecological relationship of insect, germs, and humans. In the early 1930s, the day resulted in an uneven distribution of flies caught in each ward. Two things factored in this unevenness: the actual size of the fly population and the distribution of the lower-income classes. From an ecological perspective, I argue that flies were not the cause of the disease outbreaks. Rather, these outbreaks were the results of a human-made ecosystem.