Pesky flies torment this poor dog in a Medieval manuscript from the early 1300s. Then and now, we have seen these insect vermin as an annoyance. In the Middle Ages, however, flies were associated with something far more sinister — demons.
So it was that in the fourteenth century, a poor woman called Ermine de Reims was tormented with spiritual visitations by devils, who would beat her up, threaten, and tempt her. These hellish visitors took on various disguises — sometimes looking like saints or friends, but other times like hideous beasts. After one long bout of fighting off demons, Ermine was unable to stop a group of flies from coming into her bed, crawling under her nightgown, and creeping up her body. Enmine’s spiritual councillor gave her a special flyswatter, but apparently it didn’t work on demon-flies.
Why the association of flies with Satanic forces? As Steven Connor points out in his book _Fly,_ part of the reason might be because this insect “takes its pleasure promiscuously, restlessly, unswervably, unashamedly” — in other words, these bugs could represent unfettered pleasure-seeking to morally minded Medieval folk. Of course, there is also their association with feces and pollution. Perhaps most importantly, in the Middle Ages, the evil nature of flies came from fear of a Biblically named demon called “Beelzebub,” whose literal translation is “Lord of the flies.” (See now why that book you had to read in high school makes even more sense?)
Source(s): Image Stowe MS 17, f. 48., @blogs.bl.uk/digitisedmanuscripts/2014/08/bugs-in-books.html; _The Strange Case of Ermine de Reims_, by Rebate Blumenfeld-Kosinski, 2015, Univ of Penn Press, p. 116; Steven Connor, _Fly_, 2006. Chicago: Reaktion Books, see review by Andreas Keller 2007 May 15 “A cultural and natural history of the fly,” @ncbi.nlm.nih.gov/pmc/articles/PMC1868069 .