This flying vermin shall be known as Fairies or Wisps, fairies being humanoid and winged while wisps are floating spheres, both are bioluminescent and fairies and wisps will attack each other when close by, causing the elves involved to attack each other too, mistaking each other to be evil when in fact, wisps and fairies prey on each other, wisps stealing and eating fairy eggs while fairies absorb young wisps for their magic. Of course they attack the adult forms of their predators(prey) so their young don’t get attacked
((I wonder if such a relationship exists IRL, adults of one species attacking the other species’ young and vica versa, probably not though, such a cycle would eventually bring both to extinction)) however in Dwarf Fortress, every time a spell is cast, there is a 50% chance of a fairy or a wisp spawning, a side effect of this is lone fairies or wisps being found near undead, attacking them since the undead cannot use spells, and therefore cannot help create more of them. A result of how they are born, involves young wisps and fairy eggs all over some zombies. If they were made at the same time, they’d grow up/hatch simultaneously or near simultaneously thus none are eaten/absorbed, since fairies cannot eat adult wisps and wisps cannot eat adult fairies. Another result of being born from magic is that they will not directly attack any necromancers directly