The Parasitoid Alien from the Movie Star Trek: The Wrath of Khan
Do you remember this parasitoid alien form Star Trek: The Wrath of Khan? It lives on Ceti Alpha V. Once this planet had a flourishing life until a planet near by exploded shifting its orbit and changing it into a stormy desert world.
This alien manages to adapt to new conditions and survive. It is the only non-sentient creature among parasitoid types of aliens, but just as tough and dangerous as the rest of them.
Its offspring crawls inside human ears and attaches itself to the victim's brain.
When they do that humans become very "open to suggestions". They can be controlled and manipulated into doing all sorts of mischief- for example, killing James T. Kirk...But that's not all.
As our alien friend grows inside a human brain, the host goes insane and in the end dies a very painful death.
Chances to survive this alien species seem to increase if you are a starfleet officer who happened to serve under Captain James T. Kirk. :)
