I don't watch horror movies, they do nothing for me. I will say as a child though, I saw an episode of "Outer Limits" (I think that is what is was called) and the episode was about these little spider looking martians with faces on them, and they would crawl all over people and kill them.
This absolutely terrified me, I had nightmares for a year.
Yeeeccchhhh!!!!
Those were the Zantis, exiled to Earth so that we would be the executioners for their race, who could not destroy their own.