Drone Tail-AVP2004.jpg
Biological information
Host name Any Life Form
Host type
Status Alive
Physical description
Behind the Scenes information
First appearance Alien
Last appearance
Portrayed by

Alien also knowning Xenomorph, is a highly aggressive endoparasitoid extraterrestrial species. The Xenomorphs are vicious predatory creatures with no higher goals than the propagation of their species and the destruction of any life that could pose a threat to them. Like wasps or bees, Xenomorphs are eusocial, with a fertile Queen breeding a host of subordinate castes. The creatures are known for their potent acidic blood and their pharyngeal jaws, although their biological life cycle, in which their offspring are implanted inside living hosts before erupting violently from their chests, is in many ways their signature aspect.

Aside from their repeated conflicts with humans, Xenomorphs have notably been associated with the Yautja, who know them as kainde amedha ("hard meat"). The Yautja revere the creatures as incredibly dangerous and thus highly worthy prey, notably employing them in initiation Hunts that serve to test young members of their society and mark their progression into adulthood.


"I stared into the sun. I stared into the creature's eyes. And what did I see? Nothing. It has no eyes. Neither of us have now. I saw nothing. No devil. No ultimate evil. No ultimate anything. Just bland, indifferent destruction. No more demonic than an earthquake or a plague. There is no devil. There is no god."
Ann McKay describing a Xenomorph (from Aliens: Sacrifice)

Xenomorphs are primarily solitary ambush predators, although they have been known to adopt swarm tactics when acting in larger groups. Despite their voracious ability to kill, they often seek to take their victims alive to be hosts for more Xenomorphs; victims are taken to the Hive (or simply a secluded location if no Hive exists), cocooned and/or immobilized before being impregnated with a Xenomorph embryo. However, when their target becomes a threat or is deemed unsuitable for harvest, the Xenomorph will not hesitate to quickly dispatch the chosen host.


Notably, Xenomorphs will alter their physical appearance during development depending on the physiology of the host in which they gestate – in all likelihood, this incorporation of physical traits gleaned from the host is designed to ensure the adult creature is better suited to the environment in which it will find itself. This ability to alter its form based on the host's physical attributes occurs at a cellular level and has been referred to as the "DNA reflex". Historically, most Xenomorphs encountered have typically gestated inside human hosts, and therefore adopt a basically bipedal, humanoid stance, but other variations born from a wide variety of different host organisms have been seen, and as a result feature varying physical appearances. Perhaps the most notable of these variations is the "Predalien", the result of a Xenomorph gestating inside a Yautja. However, regardless of any physical variation resulting from the host, Xenomorphs always possess certain distinctive, trademark characteristics.

Outwardly, they are encased in a tough mesoskeleton, lending them a skeletal, biomechanical appearance, and are usually colored in muted shades of black, blue or bronze. The outer shell is incredibly resilient, impervious not only to the creature's own potent acid blood, but also capable of withstanding some forms of small arms fire. Whatever organism a Xenomorph gestates within, they invariably possess distinctive, elongated, cylindrical skulls, but have no visible facial features other than their mouth. The carapace atop the head has been seen to vary, from smooth and vaguely translucent to ridged and opaque. It has been proposed that this difference is part of a maturation process, and that younger Drones possess the smoother, domed carapace, while older ones feature ridges. Notably, ridges are often visible beneath the smooth dome of Drones.

The Xenomorphs' primary weapon is their inner pharyngeal jaw, which is capable of shooting from their mouth like a piston with sufficient power to smash through bone and metal. In fact, a common tactic used by the creatures to eliminate prey is to restrain the victim with their hands, immobilizing them, before killing them with a precision jaw strike to the head, piercing through the skull and penetrating the brain; this form of attack is colloquially known as a "Headbite". On several occasions, Xenomorphs have been seen to suspend the corpses of those that they kill from ceilings.

Xenomorphs have segmented, blade-tipped tails. The sharp tip has been seen to vary from a small, scorpion-like barb to a larger, flat blade. Despite their seemingly flimsy physical construction, the creature's tail makes for an incredibly potent weapon, strong enough to impale and lift a Yautja from the floor with seemingly little effort. The tails have been used variously as stabbing, slashing and blunt force trauma weapons. Above the tails, the creature possesses several dorsal spines on its back, typically consisting of two pairs – a larger upper pair and a smaller lower pair – often with a fifth, sharper spine in the center below the base of the head. The exact purpose of these tubes is unclear.

As a result of the DNA reflex, Xenomorphs have appeared as both plantigrade and digitigrade organisms, usually in accordance with their host. For example, human- and Yautja-spawned Xenomorphs typically possess humanoid hind limbs and walk upright, while Xenomorph's spawned from quadrupedal hosts (referred to as "Runners") sport double-jointed hind legs and move predominantly on all fours. The Cloned Xenomorphs created aboard the USM Auriga also possessed digitigrade legs despite spawning from human hosts, perhaps as a result of imperfections and cross-contamination in the cloning process.

Physical abilities[]

"Men consider it evil, but it is simply doing what it does. That it does it so well is where the fear lies."
Eloise, regarding the Xenomorph (from Aliens: Purge)

When standing upright, Xenomorphs are vaguely bipedal in form, though they adopt a more hunched stance when walking or sprinting and are equally adept at moving on all four limbs, even in instances where the host was a bipedal lifeform, such as humans. They are quite capable of running and crawling along ceilings and walls and are expert jumpers. They possess great physical strength, having been known to break through metal vent covers and welded steel doors with little effort, and even of breaking down reinforced pressurized doors over time. Their large clawed talons are more than capable of tearing humans apart, while their primary jaws are capable of producing a bite strength estimated at 6,000 psi.

Xenomorphs do not radiate heat, and their body heat matches the ambient temperature of the environment in which they are found. Adverse extremes of temperature appear to have little, if any, affect on their physical prowess. In fact, physiologically they are incredibly hardy creatures – aside from being unaffected by temperature extremes that would quickly incapacitate or kill a human, they are capable of surviving in the hard vacuum of space, at least for a limited period of time. In order to succeed in their attack on enemy human vessels, the Rage equipped attacking Xenomorphs with breathing apparatus, suggesting that the creatures do require some form of atmosphere to survive for extended periods in space. One Alien on Fiorina 161 was even known to survive several tons of molten lead being poured onto it.


Xenomorphs notably lack lens-based, photosensitive visual organs. However, studies by Lasalle Bionational and Weyland-Yutani have shown that they nonetheless possess several keen senses. First and foremost, the creatures have sensory structures along the sides of their extended skulls that are capable of perceiving atmospheric vibrations (sound). Given the lengthy structure of the head, which gives the creature a wide field of "hearing", this is thought to be the Xenomorph's primary means of rationalizing its environment, a form of biological sonar similar to that employed by terrestrial bats. The creatures are also capable of detecting heat via highly sensitive thermoreactive organs located behind the skull's frontal plate – which is itself constructed of the unusual C60 carbon-lattice, known to demonstrate exceptional conductive properties. This, coupled with a highly developed olfactory sense, is thought to be how Xenomorphs locate their prey. Their sensitivity to pheromone signals would also help to explain why the Yautja Cloak is ineffective against them. Finally, despite the absence of traditional ocular organs, Xenomorphs possess largely vestigial photosensitive organs flanking the frontal plate; these rudimentary visual receptors are thought to grant the creature the necessary depth perception required when attacking prey. It is possible they also aid the creatures in seeing each other, as Xenomorphs produce no notable body heat, a fact that would otherwise render them blind to their thermal receptors.

During tests, Lasalle personnel discovered that it is possible to stun Xenomorph specimens through the use of a low-intensity ultrasound pulse, rendering them completely inert and relatively safe for manipulation and study. This discovery led to the development of weapons effective at disabling Xenomorphs, such as the Sound Cannon.

According to the research of Dr. Paul Church, the Xenomorph has a "psychic receiver" organ at the front of its head lined with compound cells of fullerite-encased hurlantium. The internal structure is solid neurons in two binary very dense fans. The fullerite and hurlantium pick up E-waves and the binary fans create interference patterns from electromagnetic fields. This allows the Alien to receive brainwaves and enables it to assess another animal's physical characteristics by seeing its subtle body. That is why strong electromagnetic fields affect the Aliens.

Furthermore, this organ atrophies when the Alien is in captivity.

Xenomorphs seemingly possess an acute sensory bond with one another, something that develops during early gestation within a host. This allows them to keep track of not only each other, but active hosts, too.

Blood and secretions[]

See also: Alien blood

Xenomorph blood is an extremely potent and concentrated molecular acid that can corrode on contact almost any substance with alarming speed. It is dull yellowish-green in color. The blood is in fact a component in a biological "battery" that provides the creatures with their energy, and seems to be pressurized inside the body so that it spurts out when wounded, as a defensive measure. This blood can prove incredibly problematic when encountering Xenomorphs aboard a starship, as using traditional firearms or explosives to attack the creature will potentially cause its blood to leak out in sufficient quantity to eat through the hull of the ship.

In some instances, Xenomorphs have been known to be conscious of the effects of their acidic blood, and even exploit it to their advantage – aboard the USM Auriga, the Lead Alien and another Cloned Xenomorph successfully escaped their containment cell by eviscerating a third, causing its acid blood to melt through the floor of the cage. Similarly, Xenomorphs on Bouvet Island, led by Grid, freed their Queen by slashing and cutting her, causing her blood to melt the chains that restrained her. Some forms of the Xenomorph have been known to "spit" acid, either as a tool or a form of attack. For example, Facehuggers have been known to regurgitate a small amount of acid to melt through obstructions between them and a potential host, such as the faceplate of a spacesuit helmet. This spitting ability has also been exhibited offensively by adult Xenomorphs; much like a spitting cobra, the creatures will spit acid to blind and incapacitate their victims rather than kill them outright. Despite their own immunity to their blood, Xenomorphs are vulnerable to hydrofluoric acid, which was used against them to great effect on LV-178.

Xenomorph Drones can also produce a thick, strong resin (vomited from their mouths) that they use to build their Hives and to cocoon their victims. This substance has the added effect of paralyzing their victims when regurgitated over their nose and/or mouth, making it easier for the creatures to move them to the Hive for implantation.

Intelligence, communication and behavior[]

"A Xenomorph might attack an armed group, but it will attack a single person for sure."
Bishop (from Alien: Bloodlines)

The Xenomorph's level of sentience is a matter of some debate. However, it is clear that they are clever and tenacious hunters. Moreover, the Hadley's Hope and USM Auriga incidents both showed that the species excels at observational learning and problem solving. In both cases, Xenomorphs managed to learn how to operate the machinery of their mechanized environments at a very basic level. On Acheron, the Xenomorphs were able to cut the power to a section of the complex to allow themselves access to their human prey, while the Queen was able to learn how to operate an elevator simply by observing it once. It has even been suggested that the Queen may have established her "nest" at the colony's main Atmosphere Processing Plant due to some understanding that such a sensitive location would afford her a degree of protection – any attackers would be unable to destroy her and her Hive without also destroying the entire facility. However, others have suggested her choice of location may simply have been the result of her selecting the warmest part of the base in which to make her nest. On the USM Auriga, captive Xenomorphs were able to use blood from one of their own kind to melt through their enclosure and escape. The Xenomorphs in the Yautja pyramid beneath Bouvet Island used a similar strategy to free their Queen from her chains.

It has been theorized that the intelligence of individual Xenomorphs may be influenced by the host. At the very least, the creatures can apparently inherit some degree of basic instinctual urges from their host, as seen when a Predalien on BG-386 was witnessed tearing a skull from a human corpse as a trophy, matching common behavior exhibited by the Yautja creatures from which the Predalien was spawned. With the distinct exception of the "Newborn" aboard the USM Auriga, Xenomorphs have demonstrated little actual emotion, save for basic self-preservation and protective instincts toward their Eggs and the Queen.

The means by which Xenomorphs communicate amongst themselves is unclear, although it is apparent from their behavior that they possess the ability to do so. While Xenomorphs are able to vocalize a variety of hisses and screeches, it seems probable that the majority of their communication is performed through some other means, possibly involving the use of pheromone release or ultrasound. Weyland-Yutani scientists have gone as far as proposing the creatures are bioelectrically "networked" in a collective hive consciousness, allowing for near instantaneous communication, simultaneous learning and unified action among all the individuals in a Hive.

The creatures possess a unique ability to inherit memories genetically, passed down from one generation to another. These memories go far beyond mere base instinct, and can include recollections of very specific events witnessed by earlier generations. According to Dr. Wren of the United Systems Military, the purpose of this genetic memory ability is to ensure the species remains intact regardless of "the differing characteristics they might have to adopt from their varied hosts".

It has been proposed that pheromone detection and the scent of their prey's fear when confronted may determine the behavior and hostility of Xenomorphs during their attacks. Documented study appears to indicate that Xenomorphs may perform excruciating, bloody kills when sensing that their victim is terrified by their presence (Lambert's death aboard the USCSS Nostromo being an example), while cleaner, faster kills take place when the prey either does not notice the Xenomorph or is less aware of its presence. It also seems that pheromone detection may help Xenomorphs to locate their prey, and that, since synthetics do not possess such chemicals, the Xenomorphs usually tend to ignore them as long as they are not disturbed.

They make few vocalizations beyond snarls and high-pitched shrieks when in pain or attacking. They regularly hiss while active, but are otherwise silent, particularly when stalking prey.

According to the research of Dr. Paul Church, the Alien also has an enormously complex neurological structure in the dorsal region of its head. He suspected this is what the Alien has instead of a brain.


Little is known regarding the Xenomorph's diet. The fact that their blood generates the energy they use to power their bodies means they may not require traditional sustenance at all. Events at Hadley's Hope on Acheron seem to imply the Xenomorphs do not use the humans they capture as a food source, as Colonial Marines who entered the Hive there found it to be littered with the corpses of colonists used as hosts, none of whom showed any sign of having been consumed, in whole or in part, despite the fact they had been cocooned for some time. Similarly, Marines from the USS Sephora found evidence that even bodies left cocooned for as long as 17 weeks were not desecrated or devoured in any way following death.

Further contradictory evidence demonstrates the precise opposite: for one, the Dragon on Fiorina 161 was apparently seen to eat at least some of the humans that it killed. The inmate Walter Golic, who witnessed an attack by the Xenomorph and escaped, also subsequently claimed that the creature "feeds on minds" (although owing to his delusional state, it is unclear how accurate this statement may be; he could simply have misinterpreted a Headbite as a form of feeding). In Gunnison, Colorado, Warriors were seen to feed on their victims. On New Galveston, hosts were known to be used as a source of food for the Hive once the embryos inside them had been born, and Xenomorphs on BG-386 were also occasionally seen to feed on humans they had attacked, sometimes while they were still alive.

It is possible that the Xenomorph's blood generates enough energy to support the creature in a state of low or moderate activity, but that food helps it replenish energy after it has been expended after a fight, chase, or any other demanding activity, thus providing an explanation for both occurrences.

Life Cycle[]

Main article: Alien life cycle

The Xenomorph life cycle is a complex process comprising several distinct stages. The creature begins its life as an Ovomorph, or Egg, laid by a Queen, which hatches a parasitoid larval form known as a Facehugger, which in turn "impregnates" a living host with an embryo known as a Chestburster. After a gestation period of several hours, the Chestburster erupts violently from the host's chest, resulting in the death of the host. The Chestburster rapidly matures to an adult phase (within a matter of hours or even minutes in some cases), shedding its skin as it grows and replacing its cells with polarized silicon. Due to the DNA reflex, horizontal gene transfer during the gestation period leads the adult Xenomorph to take on some of the basic physical attributes of the host from which it was born.

The Xenomorph life cycle bears similarities to that of certain parasitoid insect species found on Earth. Its use of a living host as an incubator for the developing infant is arguably the creature's most well-known physical attribute.


Xenomorphs operate under a caste system, with groups of specialized individuals performing distinct tasks within the species. It is not clear to what degree these castes are subject to a social hierarchy, although certain Xenomorph types, notably the Praetorians and the Queens, clearly exercise some degree of control and superiority over other more common variations.

While individual Xenomorphs have been known to operate independently, owing to their tendency to reproduce rapidly and in large numbers they are more commonly encountered in groups and often likened to an infestation owing to their tendency to spread and consume all suitable host organisms in an area. As with many other eusocial organisms, Xenomorphs, particularly in larger groups, will create a central nest or Hive in which they will reside, often overseen by an Egg-laying Queen. Raiding parties will be sent out into the surrounding area to search for and capture more hosts, which will then be brought to the Hive and used to create more Xenomorphs. In larger infestations, smaller "satellite" Hives may be created, containing just a few Xenomorphs, allowing victims to be cocooned and impregnated even far away from the Queen herself.

Genetic Offshoots[]

"The theory was, of course, that aliens without a controlling queen would branch off into different packs. Breeding might (and apparently did) give rise to bugs with recessive traits. If these bugs were allowed to continue to breed, the result would be a new race… and hurry over to start up a new hive, complete with a new queen."
―Aliens: Genocide

In the event a Queen is killed, the hive prioritizes the creation of a new Queen. In the meantime, genetic drift may occur in remaining aliens, making them "freaks" and "mutants" to the parent strain. This new strain typically doesn't exist for very long, as the new Queen will instruct her brood to destroy them, but rarely new strains are able to take root and then duel with other hives in vicious, planet-wide civil wars between hives.


While the exact origins of the Xenomorph XX121 have never been definitively determined, there have been several conflicting accounts of their origins and several notable theories on their beginnings have gained widespread recognition. The creature being artificially created by using Chemical A0-3959X.91 – 15 is the most probable cause of their origin.

Unnatural Lifeform[]

Perhaps the most prominent of these is that they are not a natural creature, but were created artificially to act as a biological weapon of war by another, technologically advanced race. Evidence suggested to support this includes the Xenomorph's general biomechanical biology and appearance, as well as the perceived "perfection" of their physical nature. Various individuals have proposed that the Engineers may be the race that created the Xenomorph, especially given their known propensity for advanced bio-weapons (including Chemical A0-3959X.91 – 15), although another (less widely-accepted) theory is that the Yautja may have been responsible, owing to their close and lengthy association with the creatures.

Following the android David unleashing the Chemical A0-3959X.91 – 15 mutagen on the Engineer homeworld, the local fauna and fungi were affected and led to the formation of certain fungus-like growths that upon being disturbed released tiny, insect-like spores that infected any and all animal life, leading to the gestation of Neomorphs. Converting an Engineer temple into a laboratory, David began conducting experiments studying the mutagenic properties of Chemical A0-3959X.91 – 15 on the indigenous life of Planet 4 and tissue samples taken from deceased Engineers, Neomorphs, and Elizabeth Shaw. Over the course of a decade, David was able to hybridize various strains of Neomorph with Shaw's mutated eggs to create Ovomorphs carrying Facehuggers that produced a non-biomechanical strain of the Xenomorph. David infiltrated the USCSS Covenant colony ship intending to continue his experiments using the crew and colonists, with the desired end result being the creation of a Queen. Whether the biomechanical Xenomorph XX121 was created by David as a direct result of further experimentation or "naturally" evolved from the Covenant strain, or even if they existed in some form prior to David's experiments, is unknown.

Species Aliens[]

Aliens Eggs[]

Facehunggers Aliens[]

Chestbusters Aliens[]

Drones Aliens[]

Warriors Aliens[]

Runners Aliens[]

Praetorians Aliens[]

Crushers Aliens[]

Spitters Aliens[]

Ravens Aliens[]

Carriers Aliens[]

Ravagers Aliens[]

Elite Guards Aliens[]

Mutants Aliens[]

Hybrids Aliens[]