Inhumi

The inhumi (masculine inhumu, feminine inhuma) are shapeshifting, vampiric creatures native to the world of Green in Gene Wolfe's series The Book of the Short Sun (though they first appear in The Book of the Long Sun in the person of Patera Quetzal). Able to fly to the world of Blue as the two planets approach each other, the inhumi have been an endemic scourge there. Their native form is something like a flying, reptilian leech, but as they feed on the blood of a creature, they become more like it, psychologically and spiritually.

They are responsible for destroying the Neighbors' civilization and driving them from their homes and planet.