Facehugger

A facehugger is the second stage in the Alien's life cycle. It has eight long, finger-like legs, which allow it to crawl rapidly, and a long tail adapted for making great leaps. These particular appendages give it an appearance somewhat comparable to chelicerate arthropods such as arachnids and horseshoe crabs.

The facehugger is a parasitoid; its only purpose is to make contact with the host's mouth for the implantation process by gripping its legs around the victim's head and wrapping its tail around the host's neck. Upon making contact, the facehugger administers a cynose-based paralytic in order to render it unconscious and immobile. During a successful attachment, the facehugger will insert a proboscis down the host's throat while simultaneously implanting an embryo. The host is kept alive, and the creature breathes for the host. Attempts to remove facehuggers generally prove fatal to the host, as the parasitoid will respond by tightening its tail around the host's neck, and its acidic blood prevents it from being cut away. In addition, its grip on the host's head is strong enough to tear the host's face off if it is forcibly removed.

Once the Alien embryo is implanted, the facehugger will remain attached until the implant is secure, which can take anywhere from less than a minute to 16 hours. Once this happens, the parasite detaches, crawls away, and dies. The victim awakens with no awareness of the implantation, believing themselves to have been asleep, and appears to have a normal, healthy bodily function.

According to AVPR: Science of the Xenomorph, a behind-the-scenes documentary on Aliens vs. Predator: Requiem, it is theorized that facehuggers may implant a viral agent that "commands" the host's cells to grow the chestburster, as opposed to an implanted embryo. This is an alternate explanation to horizontal gene transfer as to how the resulting Xenomorph is able to adopt the characteristics of its host.

Giger's original design for the facehugger was a much larger creature with eyes and a spring-loaded tail. Later, in response to comments from the filmmakers, Giger reduced the creature's size substantially. At first, Giger assumed that the facehugger would wrap around the outside of the astronaut's helmet, but Scott decided that it would have far more impact if the facehugger were revealed once the helmet was removed. Scott and Giger realized that the facehugger should burn through the helmet's faceplate with its acid blood; subsequent redesigns of the space helmet included a far larger faceplate to allow for this. Dan O'Bannon initially conceived the facehugger as somewhat resembling an octopus, possessing tentacles. However, when he received H. R. Giger's designs, which substituted tentacles with fingerlike digits, he found Giger's design concept to be superior. Since no one was available at the time, O'Bannon decided to design the facehugger prop himself. The technical elements of the musculature and bone were added by Ron Cobb. Giger's initial design for the smaller facehugger had the fingers facing forward, but O'Bannon's redesign shifted the legs to the side. When the foam rubber sculpture of the facehugger was produced, O'Bannon asked that it should remain unpainted, believing the rubber, which resembled human skin, was more plausible.

In Aliens, the facehuggers were redesigned by Stan Winston so that they would be capable of movement. Unlike the creatures in the first film, the creatures would take a much more active role in impregnating their victims. When Ripley throws one off her, the facehugger was now capable of scuttling across the floor and leaping at its prey, wrapping its tail around the victim's throat. The facehugger is also shown to be capable of independently surviving outside of its egg. Due to the film's budget, only two fully working facehuggers were built.

In Alien 3, another addition, a "super-facehugger" that would carry the embryo of the queen Alien, was planned, but ultimately dropped. The super-facehugger is briefly glimpsed in the Assembly cut of Alien 3, but not identified as such. It made a brief appearance in the canonical Alien book called Alien: Sea of Sorrows, set a while after the events of Alien Resurrection, about the grandson of Ripley Clone 8, Ellen Ripley's clone.