Alien (Xenomorph)
Intervacius raptus
Sapience level Semi-sapient
Average height 7-8 ft. (drone)

15 ft. (queen)

Average weight 136-176 kg
Diet Carnivore
Social unit Colony (w/ caste system)
Population status Abundant
Subspecies see below ↓

More Alien vs. Predator species

Xenomorphs (more commonly referred to simply as Aliens) are an extraterrestrial species of insectoid parasites with elongated heads.

Among the deadliest of all known alien species, Xenomorphs need a host organism in order to reproduce. Unlike many other extraterrestrial races, they 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 Xenomorph biological life cycle, in which their offspring are violently implanted inside living hosts before erupting from their chests, is in many ways their signature trait.

Anatomy and appearanceEdit

When standing upright, Xenomorphs are vaguely bipedal in form, though they adopt a more hunched, quadrupedal stance when walking or sprinting. They have a skeletal, biomechanical appearance and are usually colored in muted shades of black, blue or bronze. Aliens do not radiate heat, as their body heat matches the ambient temperature of the environment in which they are found. Drones have the ability of running and crawling along ceilings and walls. They have great physical strength, having been shown to be capable of breaking through welded steel doors.

Xenomorphs also have segmented, blade-tipped tails. As a weapon, the strength of the tail is very effective, having been shown to be strong enough to impale and lift a Predator with seemingly little effort. They are also adept at using their tails as blunt weapons, sometimes to deadly effect.

They have elongated, cylindrical skulls, but possess no visible eyes. How the creatures see is uncertain. The xenomorphs' inner jaws are powerful enough to smash through bone and metal. Throughout their appearances, human-spawned drones have been shown to have a fluctuating number of fingers. Originally, the creature has webbed, six fingered hands. The number of fingers is reduced to three in Aliens, and are shown to be much longer and more skeletal. Later, the number of digits is increased to four, with two long middle fingers and a pair of thumbs.

Both plantigrade and digitigrade organisms, drones' appearances usually vary in accordance to their host. Human-spawned drones have humanoid hind limbs, while dog-spawned drones sport double-jointed legs due to its quadrupedal host.

Xenomorph 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. Facehuggers can spit this acid in order to desolve surfaces preventing it from infecting a host, some drones retaining this ability as well. Some have suggested the idea that the creatures have acid blood as a plausible means to make the creature "unkillable"; if one were to use traditional firearms or explosives to attack it, its blood would eat through the hull of a ship. It has been suggested that, at least at the "facehugger" stage, the acid is not blood but a fluid maintained under pressure between a double layer of skin. Drones are shown to be conscious of the effects of their acidic blood, and even use it to their advantage: two are able to escape a cage by killing a fellow drone so its acid eats through the cage floor; a queen being held by chains apparently instructs several drones to slash and cut her, thus corroding the chains. It is theorized that the Aliens' acid blood could be some type of "hydrosulphuric acid" composition due to its corrosiveness and the conspicuously toxic effects on living human tissue. It is also speculated that xenomorphs are immune to their own acidic and toxic liquids due to a endobiological build-up similar to the human stomach's ability to protect itself from its digestive fluids. This theory is taken one step further and speculates that the organisms' protection system against its own toxic hydrosulphuric acid is protecting the rest of the organism with what is basically a bio-organically produced Teflon isolation. The xenomorphs' chitinous hide can be used as an effective armor against their own acid.

Xenomorphs can produce a thick, strong resin (secreted from their maws, giving them the look of a slavering beast) that they use to build their hives and to cocoon their victims, and they can use the walls of their hives as camouflage.

Behavior and intelligenceEdit

Xenomorphs are eusocial life-forms with a defined caste system which is ruled over by a queen.

Events on the LV-426 colony and USM Auriga showed that the species excels at observational learning and problem solving. In both cases, the xenomorphs managed to learn how to operate the machinery of their mechanized environments at a very basic level. On LV-426, the Aliens were able to cut the power from a section of the complex to allow themselves access to the humans. The queen was able to learn how to operate an elevator simply by observing it once. The queen establishing her 'nest' at the base's main power plant could equally be the result of her selecting the warmest part of the base to make her nest or her deliberately selecting a location where any attackers would be unable to destroy her without destroying the entire facility. On the USM Auriga, they were able to use blood from another xenomorph to melt through their enclosure and escape, with drones in an Antarctic temple using a similar strategy to free the queen from her chains. With the exception of the "Newborn", xenomorphs have demonstrated little actual emotion, save for self preservation and maternal instincts toward their eggs. Xenomorphs communicate via an empathic or telepathic bond.

Life cycleEdit

The Alien 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. It is theorized that this parasitoid would not likely be able to use a host any smaller than a cat, or as large as an elephant.

The facehugger then "impregnates" the host with an embryo known as a "chestburster," which, after a gestation period of several hours, erupts violently from the host's chest resulting in the death of the host. The chestburster then matures to an adult phase within a few hours, shedding its skin and replacing its cells with polarized silicon. Due to Horizontal gene transfer during the gestation period, the Alien also takes on some of the basic physical attributes of the host from which it was born, allowing the individual alien to adapt to the host's environment.



Queen xenomorphs are significantly larger and stronger than the warriors. Their body structure differs also, having two pairs of arms, one large and one small. The queen's head is larger than other adults and is protected by a large, flat crest, like a crown, which are unique from queen-to-queen.

Unlike other Aliens, the queen also has high heel protrusions from its feet. Pregnant queens possess an immense ovipositor on their lower torso, similar to a queen termite's, which is responsible for creating eggs. The queen is able to detach from the ovipositor. When attached to its ovipositor, the queen is supported by a "biomechanical throne" that consists of a lattice of struts resembling massive insect legs.

Unlike insect queens, there appears to be no need for drones to fertilize an Alien queen's eggs. There is also a form of oral implantation, by which the "Predalien" mimics the action of facehuggers, directly depositing multiple chestburster embryos into a host via its inner jaw. This is a stage between adult and queen known as Praetorian, by which a young queen attempts to quickly build its army before it grows the egg sack and cannot defend itself.


The eggs laid by the queen are large, ellipsoidal leathery objects between two to three feet high with a four-lobed opening at the top. As a potential host approaches, the egg's lobes unfold like flower petals, and the parasitic facehugger extracts itself from the egg and attaches itself to the potential host.



The facehugger is the second stage in the xenomorph'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 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 tightens its tail around the host's neck in order to render it unconscious through oxygen deprivation. The facehugger then inserts a proboscis down the host's throat, supplying it with oxygen whilst simultaneously implanting an embryo. Attempts to remove facehuggers generally prove fatal, as the parasitoid will respond by tightening its grip, and the facehugger's acidic blood prevents it from being safely cut away. Once the embryo is safely implanted, the facehugger detaches and dies.



After implantation, facehuggers die and the embryo's host wakes up afterwards showing no considerable outward negative symptoms. Symptoms build acutely after detachment of the facehugger, the most common being sore throat, slight nausea, increased congestion and moderate to extreme hunger. In later stages where the incubation period is extended in preparation of a queen birth, symptoms will include a shortness of breath, exhaustion, and hemorrhaging (detectable through biological scanners and present in nosebleeds or other seemingly random bleeding incidents), as well as chest pains inflicted either in lack of chest space due to the chestburster's presence, or even premature attempts to escape the host. The incubating embryo takes on some of the host's DNA or traits, such as bipedalism, quadrupedalism or possessing the mandibles of a Predator and other body structure changes. Over the course of 1–24 hours, indeterminable in some cases, and sometimes up to a week, in the case of some queens, the embryo develops into a chestburster, at which point it emerges, violently ripping open the chest of the host, killing it.

Growth and maturityEdit

When a chestburster erupts from the body of its host, it is less than 1 foot tall. However, it soon undergoes a dramatic growth spurt, reaching adult size in a matter of hours. The chestburster often molts several times before reaching maturity. The creature's final limbs do not grow in the earliest stages.

Xenomorph varietiesEdit

Aliens take on various forms depending on the characteristics of their hosts. Most of the Aliens seen to date have been human-spawned, but a number of Aliens born from other hosts have also been seen.

Predalien (from Predator host)Edit


The Predalien shares many characteristics with its host, such as long hair-like appendages, mandibles, skin color and similar vocalizations. It is a large, bulky creature, and possesses physical strength greater than that of human-spawned drones. Like human-born xenomorphs, it is also shown to be stronger than its host species, as evidenced by its ability to pin, push, and knock a Predator away with ease. It also possessed the ability to impregnate human hosts with multiple embryos. It also has the ability to control drones and warriors.

Runner Alien (from dog host)Edit

The runner shares the same basic physical conformation and instincts as the other drones, although there are several differences due to the fact it was spawned from a dog. The runner in its chestburster form is a miniature version of the adult, unlike the larva-like human spawned chestbursters. The adult is primarily quadrupedal, has digitigrade hind legs and lacks the dorsal tubes of the human-spawned variety.


Due to significant genetic tampering in an attempt to recover DNA from the deceased Ellen Ripley and the queen embryo within her, the resulting cloned xenomorphs show a number of minor human traits. The cloned queen inherits a womb, and as a result it ceases to lay eggs and gives birth to a humanoid mutant. Physically, the human-xenomorph Newborn is very different from its brethren, being larger, with pale, translucent skin, a skull-shaped face with eyes, a human tongue and complete absence of a tail. The Newborn fails to bond with its xenomorph mother, and kills it. Instead, the Newborn sees the Ripley clone as a surrogate parent. Its' blood was reddish, but still acidic.