That's terrifying.
Ever read The Animorphs series? by Katherine Applegate and her husband Michael Grant, writing together under the name K. A. Applegate
"Yeerks are parasites. A Yeerk enters a host through the ear canal, flattens itself out on the brain, and takes over completely. The host creature can't scratch an itch unless the Yeerk wants it to. We call a being who has been taken over that way a Controller. You must be thinking the Yeerks are pure evil. But let me tell you what it's like to be a Yeerk who isn't in a host. Yeerks are basically gray slugs. No hands, no legs, no eyes, no ears. If a Yeerk wants to be free, free to really move, free to see the beauty of the world around it, free to hear music or even the sound of rain on leaves, if a Yeerk wants that, it has to have a host. If a Yeerk wants to be free, it has to make another living creature a slave. Not an easy choice, is it?"
―Cassie
The Yeerks are a parasitic species of slug-like creatures who require host bodies to see, walk and verbally communicate. They have made it their mission to search the galaxy and enslave other species.
Ohhhhh, no I haven't read any of their stuff. That extract looks right up my street! I'll add them to my reading list. Looooovvvve the name Yeerk! :)