Face hugger

A truly frightening creature from the Alien series of movies. It's the larval state for the xenomorph species which hatch from eggs laid by the queen. They wander around until they find a suitable host, at which time they leap on its face, paralyze it with venom, and jam a tube down its throat. The tube keeps the victim alive until it implantes an "egg" inside its chest. The facehugger then falls off and dies. About 24 hours later, a chestburster erupts from the victim, killing it, and scurries off to grow to full size.

In the Aliens vs. Predator computer game, it's the worst thing to run into. The game is dark, creepy, and dramatic to start with, and then you hear a light scraping sound as a facehugger crawls around the floor towards you. The rooms are very dark. The facehugger is black. Then it smacksup against the screen, ending the game and inducing a fatal heart-attack for the player.

In the film- Alien, this was one of the manifestations of the killing machine from outer space. The creature, designed by H.R.Giger, evolved during the course of the film. It's second incarnation, after emerging from an egg sack, was a slimy, octopus looking creature that attaches to the face of a host animal (in this case a unwitting human). It wraps its tail around the throat of this person, preventing removal. The face hugger has an acid based circulation, so when cut into spills a substance that eats through the steel floors of the spaceship.

It uses the host animal for both a food source and as a breeding ground.

It reappears in the Alien sequels.

It's not pretty