Facehugger

The Facehugger appeared in 1979 movie called Alien. The facehugger is the second stage in the life cycle of a Xenomorph. Its bony finger-like legs allow it to crawl rapidly and its long tail can launch it in great distances. These particular appendages give them an appearance somewhat comparable to chelicerate arthropods such as arachnids and horseshoe crabs.

The facehugger is a parasitoid; its only purpose being to make contact with the host's mouth for the implantation process. The Facehugger secures its eight finger-like appendages tightly around the head of its victim and wraps its tail tightly around the host's neck, eliciting a gasping response and allowing the insertion of an ovipositor into the host's esophagus.

An embryonic form of the Xenomorph is then implanted directly into the stomach of the host. During the implantation process the host is fed a constant supply of oxygen via two lung like organs. Attempts to remove the Facehugger result in the parasite tightening its tail around the host's neck, almost as a threat of death if not allowed to continue the implantation process. Another deterrent is its highly pressurized molecular acidic blood which sprays wildly if the parasite's skin is cut into, ensuring that if it is removed from the host surgically the host will suffer catastrophic burns, almost certainly leading to death.

As the implantation process nears completion the facehugger's epidermis solidifies into a chitinous layer of silicon, presumably in an attempt to ensure the success of the implantation. Once the embryo is safely implanted, the parasite detaches from the host and retreats to die in seclusion. Eventually, the larval form of the Xenomorph, known as a Chestburster, will violently erupt from the host's chest cavity, resulting in a gruesome and excruciating death.

While still residing within the Ovomorph, the facehugger appears to possess the ability to assess the physical viability of a potential host, including being able to discern the difference between living and artificial beings. The parasite will generally avoid hosts with obvious deformities or maladies, choosing instead to remain within the Ovomorph.