the Silmarillion, on Melkor’s corruption of the world before the second great war.
flies are bred by Morgoth? this doesn’t make any sense, though! everything else we’ve seen bred by Morgoth is evil, like orcs and werewolves and dragons and aforementioned monsters of horn and ivory that dye the earth with blood. (sidenote: fuck, Tolkien would write some incredible horror novels). But flies are great! Detritivores are an important part of a sustainable ecosystem! Unless literally no plants or animals ever died in the Valar’s first vision of Earth, we need flies. And maybe that’s actually it - everything was eternal, including every single blade of grass. Maybe Morgoth’s original role, if he hadn’t fucked it up, would have been inspiring the other Valar away from a design-a-perfect-thing-keep-it-that-way model. Because real ecosystems don’t have an equilibrium (this was a common mistake made by early ecologists), they are inherently disruptive and unsustainable and healthier for it.
Instead he lit whole continents on fire, which is the wrong sort of disruptiveness. But still, the flies are necessary, they didn’t do anything wrong.
I think I prefer to believe that Oromë and Vána, who understand the cyclical nature of healthy ecosystems on account of being the Vala of hunting and the Vala of eternal youth (which I interpret as ‘renewal’), collaborated on the invention of flies and then Morgoth corrupted them into mosquitos, which are totally evil and ecologically unnecessary.
mosquitos are to flies as orcs are to Elves, basically.