The inhumi are shapeshifting, vampiric creatures native to the world of Green in Gene Wolfe

Gene Wolfe

Gene Wolfe is an American science fiction and fantasy writer. He is noted for his dense, allusive prose as well as the strong influence of his Catholic faith, to which he converted after marrying into the religion. He is a prolific short story writer and a novelist, and has won many awards in the...

's series The Book of the Short Sun

The Book of the Short Sun

The Book of the Short Sun is a trilogy by Gene Wolfe, comprising On Blue's Waters , In Green's Jungles , and Return to the Whorl . It is the sequel to Wolfe's tetralogy The Book of the Long Sun, and has connections to The Book of the New Sun...

 (though they first appear in The Book of the Long Sun

The Book of the Long Sun

The Book of the Long Sun is a tetralogy by Gene Wolfe, comprising Nightside of the Long Sun, Lake of the Long Sun, Caldé of the Long Sun, and Exodus from the Long Sun. The first two volumes are published together as Litany of the Long Sun and the last two as Epiphany 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.