It was thought that only Orcs, Trolls, Spiders and some men dwelt in the realm of Mordor, but it was little known that there was another beast that tormented any people who entered Mordor. It was said that the Dark Lord 's power was spread to the smallest evil in his land, creating the Flies. At the end of the Third Age, the flies were a nuisance to Frodo and Sam as they crossed the Morgai towards Mount Doom.
Portrayal in adaptations
Flies appear in both Middle-earth: Shadow of Mordor and its sequel Middle-earth: Shadow of War, where they are referred to as "Morgai Flies". The flies can be disturbed by cutting down their nests, after which they will attack nearby Uruks.