Facehugger

The facehugger is the 2nd stage of a Xenomorph. After hatching from an egg, the facehugger must attach itself to a host in order to implant an alien embryo. The facehugger will stay tightly secured to it's host for a few hours, and then slip off.  The hugger also feeds it's host oxyen, as it implants the embryo. Once it is finished, it crawls away from the host and dies.