Trope-a-Day: Puppeteer Parasite
Puppeteer Parasite: Mostly not naturally (due to the aversion of No Biochemical Barriers), but infectious neuroviruses can do a damn good impression of this – which is the sort of thing that makes defense planners twitchy, but no-one’s done it on a large scale yet (as mentioned under Alien Invasion), mostly because of what happens to people who earn that place on the Top Ten Galactic Atrocities List.
Another theoretical possibility – which as far as people know hasn’t been done at all – would be to encode a mind-state in a self-replicating/self-modifying infectious neurovirus to make a true puppeteer parasite clade. Squicky.
But still, it’s nice to know there’s a firm-SF plausible way to do this: