The Alien is a fictional endoparasitoid extraterrestrial species that is the primary antagonist of the Alien film series. The species made its debut in the 1979 film Alien.
Unlike many other recurring enemy extraterrestrial races in science fiction, the Aliens are not an intelligent civilization, but predatory creatures with no higher goals than the propagation of their species and the destruction of life that could pose a threat. Like wasps or termites, Aliens are eusocial, with a single fertile queen breeding a caste of warriors. The Aliens' biological life cycle involves traumatic implantation of parasitic larvae inside living hosts, which mature before erupting from the host's chest. Their design deliberately evokes many sexual images, both male and female, to illustrate their blurring of human sexual dichotomy.
The Alien design is credited to Swiss surrealist and artist H. R. Giger, originating in a lithograph called Necronom IV and refined for the series' first film, Alien.
When standing upright, the Aliens are vaguely bipedal in form. They have a skeletal, biomechanical appearance and are usually colored in muted shades of black, blue or bronze. Their body heat matches the ambient temperature of the environment in which they are found, so they do not radiate heat, making them invisible to infra-red vision.
They have elongated, cylindrical skulls, but possess no visible eyes. In Aliens, the adult creatures have a more textured head rather than a smooth carapace. In the commentary for Aliens, it was speculated that this was part of the maturation of the creatures, as they had been alive far longer than the original Alien.
Blood and secretions
Alien blood is an extremely potent acid and is capable of corroding on contact almost any substance with alarming speed. It is dull yellowish-green in color, and seems to be pressurized inside the body so that it spurts out when punctured. Ron Cobb suggested the idea that the creature have acid blood as a plausible means to make the creature "unkillable".
Aliens can produce a thick, strong resin that they use to build their hives and to cocoon their victims, and they can use the walls of their hives as camouflage.
Aliens are eusocial life-forms with a caste system ruled over by a queen. Their life cycle comprises several distinct stages: they begin their lives as an egg, which hatches a parasitoid larval form known as a facehugger, which then attaches itself to a living host by, as its name suggests, latching onto its face. The facehugger then "impregnates" the host with an embryo known as a "chestburster", which, after a period of gestation, erupts violently from the host's chest resulting in the death of the host.
The chestburster then matures to an adult phase, shedding its skin and replacing its cells with polarized silicon. The adult phase of the Alien is known by various different names. The adult Aliens have been referred to as "drones," "warriors," "workers," and sometimes "soldiers," similar to the way ants have been defined.