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 one of the characters). Green sometimes passes close enough to its sister world Blue that the inhumi can launch themselves through the void between the worlds and descend to Blue. After Blue's colonization, they begin commandeering landers to make the crossing less risky. 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.