The Flies of Mordor were tiny beasts that dwelt in Mordor. These bloodsucking insects were loud, hateful, and hungry.
It was thought that only Orcs, Trolls, Spiders and some men dwelled 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.
- A Tolkien Bestiary