Isidore of Seville [7th century CE] (Etymologies, Book 12, 7:): The cynomya is named with a Greek word, skýlos, that is dog. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Worms 9.13): Cynomia is a worm, as Isidore says, which in Greek is called a dog-fly [musca canina], for a cino is "dog" in Greek. This fly is bothersome to the ears of the puppies, and although they frequently shake them, they always fly back in an intrusive manner; but where they find the puppies too lazy to shake themselves, they continue aggressively even to causing bleeding and wounds. And in this it signifies the devil, whose suggestions, if any one receives in the negligent ear of the mind that which should be discarded, he inflicts a wound by the consent of sin or pleasure. With Abraham, then, drive away the flies and the birds of evil thoughts, and this on the rod which is the sign of the cross. For David came to Goliath with a staff, and Jacob crossed the Jordan with a staff. - [Badke translation/paraphrase]