Isidore of Seville : In the fourth place, Egypt is struck with flies. The fly is an insolent and restless animal. What does it stand for except the arrogant concerns of carnal desires? Egypt is struck with flies because the hearts of those who love this world are battered by the disquiet of their desires.The translators of the Septuagint put cynomyia here, which means "dog fly." This word meant the habits of a dog, in which the pleasures of the mind and the indulgence of the flesh are constantly expressed. By dog fly this passage can also mean the eloquence of lawyers, which they use to tear at one another like dogs. — QUESTIONS ON THE OLD TESTAMENT, Exodus 14:8-9 Jerome : Kynomyia does not represent "dog fly," as the Latins translated it, with the Greek letter upsilon; according to the sense of the Hebrew the diphthong oi should be written so that the word is koinomyia, that is, "every genus of flies." — LETTER 106.86