Xenomorphs

> A perfect organism. Its structural perfection is matched only by its unmatched hostility. I admire its purity. A survivor. Unclouded...by conscious...remorse...or delusions of morality.
>
> Joshua, about Xenomorphs

**Xenomorphs** (Latin, Internecivus raptus, "*murderous, deadly*" and "*seized*"), better known as the Alien, are a highly aggressive, endoparasitoid extraterrestrial species with multiple life cycles, possibly originating from the planet Proteus (also known as Xenomorph Prime). Arguably the deadliest of all known alien species, these creatures need a host organism in order to reproduce.

The Xenomorphs are 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.

The appearance of the Xenomorph varies depending on its host. The human phenotype is generally around 7–8 feet, and roughly 136.0 to 181.4 kilograms with a long, muscular tail and large, curved, oblong head. The Queen of the species is generally twice as large and possesses superior speed, strength and intelligence. The term Xenomorph is derived from the Greek words xeno ("stranger", "alien", and "foreigner") and morphe ("form", "shape").

## History

### Origins

While the origins of the Xenomorphs have never been definitively determined, several notable theories on their beginnings have gained widespread recognition. 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. To date, no conclusive evidence has been discovered either way.

There are no solid facts as to the origins of the Xenomorph species; instead, there are many assumptions which cannot be confirmed. Based on the limited information, the most commonly accepted hypothesis is that they are an artificially created species, although another hypothesis says that they evolved naturally on a planet much different than our own. Another Theory is the Deacon from Prometheus evolved into the first primitive Xenomorph though there is evidence stating that this is false.

The Xenomorph could be the result of genetic manipulation by Mala'kak (also known as the "Engineers" or "Space Jockeys") as a terraforming mechanism about ten million years ago. This theory has been twisted slightly by Prometheus, as they created an artificial subspecies, the "Deacon" orproto-alien, when the Mala'kak brought containers filled with an unknown substance (it closely resembles Xenomorph secretions in hives). This substance, mutated harmless organisms into somewhat hostile creatures. When humans "infected" with this substance, mate with one another it produced a different subspecies of "octo-facehuggers" that can grow incredibly large. As shown in the movie, this new subspecies regardless of who it infected, Mala'kak or human, would result in the "Deacon" or Proto-alien. It is not known what new subspecies would result if the "octo-facehugger" impregnates a Yautja. As a result, over the years the Xenomorph has become an entirely new species in the galaxy.

Another theory, commonly accepted, touched on in the expanded universe is they were the alpha predator of their own ecosystem on a nightmarish and harsh planet, (some assume it to be Xenomorph Prime, but there is no solid evidence) but were spread throughout the universe as a food source and a delicacy to a species with a natural immunity to their acidic blood. Without their native ecosystem to keep them in check, they have since run rampant and infested their own kind, and developed into a separate dominate species. Other parts of the universe began to take notice in this interesting species and began them. The Mala'kak, the Yautja, Humans, and an unspecified highly technological humanoid species introduced in the comic Alien: Reaper began using them as means of sport, terraforming mechanism, as biological weapons, food delicacies, and scientific experiments.

One idea though, is that they were created by the Mala'kak as biological weapons against an unknown threat or a weapon to wipe out humanity, and the eggs at the derelict ship found at LV-426 was in fact a biological weapon that turned against the crew. Ridley Scott states during the Director's Commentary on the Alien Special Edition DVD that the eggs are the cargo of the Space Jockey's ship with the ship being a sort-of war ship designed to carry these biological weapons, or perhaps a science vessel carrying the eggs as cargo for scientific study.

## Biology

The Xenomorph physical form varies wildly depending on its life stage, hive caste, age and host, with numerous genetic varieties existing whose origins are completely unknown, as well as varieties which have been genetically engineered by other host species or genetically grown. The typical Xenomorph starts life as an egg-like creature which, when detecting the presence of a potential host, opens up to release the second stage: a small quasi-arachnoid life form which launches itself onto the host's face and impregnates it with an endoparasitoid larva, which later consumes the host from within and exits the body as a vaguely worm-like organism called Chestburster, which then grows very quickly, developing into the adult Xenomorph.

Although several and even numerous varieties exist, the adult Xenomorphs all tend to share some common traits: a vertebrate-like body, a protective exoskeleton, a long flexible tail, an elongated domed head, with nearly invisible eyes near the mouth, and a toothed maw which hides a retractable inner mouth. Little is known about their biology, but it is known that they eat with their "tongue mouths", not their outer mouths. This mouth is somewhat similar to the pharyngeal jaw of a moray eel. They also bleed extremely acidic fluid which is yellowish green in color and often referred to as "blood", although whether it's used to transport nutrients through the body and/or serves other functions is not clear.

While the extremely acidic fluids and tremendous resilience displayed by the creature might suggest an alternative kind of biochemistry, the fact that the Xenomorph not only feeds on Humans but actually develops inside them strongly suggests that its biology is carbon-based. The ability to inherit traits from its hosts also suggests that it incorporates genetic material from them, implying that the Xenomorph either has DNA, or is able to read and convert DNA into whatever means it uses to store genetic information.

## Variations

The Xenomorph has been portrayed in noticeably different ways throughout the film series. Much of this was due to the continuing advancements made in the field of special effects, technology, and techniques used to bring it to life.

It has also been shown, both on-screen and in the games based on the Alien series, that the Xenomorph's form is affected by its host, so that different species of hosts will create different varieties of Xenomorph. An example of this is seen in Alien³, when a dog (an ox in the extended edition) spawns a Xenomorph with a distinct canine body structure, quadrupedal movement, and greatly enhanced speed.

### Upper Body

Xenomorphs are depicted as tall, slender creatures with a roughly human biomechanical design. The chest area appears to be rib cage-like in design. In later films, such as Alien: Resurrection and Alien vs. Predator, they are depicted as being shorter and bulkier organisms, as well as being more quadrupedal, portrayed by either stuntmen in suits for close-ups, or computer-generated imagery for their full form.

In Aliens, Xenomorphs are depicted as having ridges along their cranium, while in all other films they have smooth cowls covering their skulls. It was speculated in the Aliens bonus DVD that this was due to these Xenomorphs having had more time to mature, compared to the Xenomorphs in the other films.

In the comics and various video games (Aliens vs. Predator: Extinction, Alien vs. Predator (SNES), Aliens vs. Predator 2), this was depicted as one of the visual differences between the Xenomorph Drone and Warrior castes. The Drones (in this instance used to indicate a "worker" caste, instead of mating-capable males) have the smooth cowl while the Warriors display the ridges. The Drones and Warriors have different tasks: warriors defend the hive, and drones hunt potential hosts, while some live only to protect the queen, such as hive warriors or praetorians.

In Alien and Alien³, the Xenomorph has six fingers, with the index and middle fingers conjoined into one digit, ring and little fingers also conjoined, and thumbs on both sides. In Aliens, the Xenomorphs are shown with five fingers, with the second thumb missing. In Alien: Resurrection and Alien vs. Predator, the aliens have four fingers, though the middle two appear to be a fusion of two digits. No explanation is given in the films for the fluctuating number of digits (this being similar to Yoda's digit numbers in the Star Wars series changing each film).

### Lower Body

In Alien and Aliens, the Xenomorphs were plantigrade. In Alien³, the Xenomorph is digitigrade, owing to its quadrupedal host organism (a dog in the theatrical cut, an ox in the extended version). Alien: Resurrection saw a dramatic redesign from previously-encountered human-spawned breeds: the Xenomorphs that emerged from human hosts in this film walked on digitigrade hind legs in a manner that does not conform with the appearance of previously-seen members of the breed. This is complicated by the fact that the Xenomorphs of the film were spawned by a Queen grown from cells derived from a clone of Ripley, making their genetic heritage muddled at best.

In Alien vs. Predator, the Xenomorphs return to their roots as plantigrade organisms, though their legs are sleeker and more skeletal in appearance, due to the use of computer visuals and hydraulic puppetry, rather than costumes.

Originally, the Xenomorph's tail was roughly the length of the rest of its body, with a small, almost surgical stinger-like barb on the end; but from Alien³ onwards, the tail has extended in length and features a large, knife-like blade at the tip.

In Alien: Resurrection and Alien vs. Predator, the tails have also supported a ridge of spikes right before the blade. This was introduced in Alien: Resurrection to help them swim convincingly, and was left intact in Alien vs. Predator. The tail itself is shown to be of incredible length during Alien vs Predator, measuring almost its full body length.

The original shooting script for Aliens featured a scene in which Lieutenant Gorman was "stung" by a Xenomorph's stinger. He was not killed, merely stunned, and the barb remained lodged in his shoulder, having torn loose from the Xenomorph's tail much like a bee stinger. The novelization also included this scene, though the final cut of the movie does not. This attribute is used later on in various games.

### The Head

The most notable feature of the Xenomorph species is the elongated, banana-shaped head. This aspect is both disturbing and terrifying, combining visual elements that are usually blocked by our conscious mind with others resembling vaguely human features. Though it appears to lack any sort of optical vision components (such as eyes), it is believed that it "sees" by sensing pheromones. This can neither be confirmed nor denied, but is the most widely-accepted hypothesis due to the fact that a Drone will not kill a host body already infected (as seen in the movie Alien 3 and the book Aliens: DNA War). There has been one detail on an alien's head that may be an eye being so small and the same black as the skin. It is hard to see if these are eyes or an implant on the skin (you can see them on the front cover of the Aliens vs Predator 2010 video game and very rarely as a predator in alien vision).

Other proposed conjectures include that the eyes are similar to a desert-burrowing lizard's eyes; meaning that they lay under a thin layer of skin, yet are deep enough that they are not visible from the outside. Another idea is that their whole head is one big insect-like eye, but there is no proof of this. In Alien 3, the fish-eye lens represented the Runner's sight, but it is unknown if this is really how it sees.

Despite this, the Xenomorphs could theoretically see. This is seemingly lent support by early models and toys of the Warrior Xenomorph while Alien was still the only existing movie in the timeline. These showed an actual, physical, humanoid skull built under the smooth carapace, with the smooth top working like a one-way visor.

### Dorsal Spines

Along the back of most Xenomorphs' bodies are a series of appendages that appear to have no function. It's still in debate what they are used for, with theories ranging from sensory organs to communication organs, to breathing apparatus, to defensive mechanisms, to structures that dissipate heat, to storing substances their bodies need, or to provide structures to carry around the young, underdeveloped chestbusters, the eggs or the facehuggers. None of these ideas has been confirmed or denied by official sources so far.

One theory is that the four back appendages are used as a type of radar that the alien uses to see through extreme environments or detect movements. However in the extended universe it is said that the dorsal spines are used to secrete and possibly store the resin used to build their hives.

It is interesting to note that, in the Alien vs. Predator Volume 1 comic, Xenomorph Drones bury themselves in the ground, yet their spines are still shown just breaking the surface, implying some use when connected to the environment. This may be either biological (breathing, heat exchange, etc.) or sensory (detecting the vibrations of marines walking on the ground above).

Other hypotheses include:

* Perhaps the spines separate the dominant Xenomorphs from the weaker ones, for example, the smaller the spines, the weaker the Xenomorph, the bigger, the stronger.
* The creatures might come from a mainly amphibious planet, and perhaps the spines are a mechanism to swim underwater faster to catch prey. They do not seem all that hydrodynamic, but it's possible to suppose the spines might be used for stability, like the dorsal fins of a dolphin (not that their shape seems very much efficient at that either).
* The spines might be spiracles that take in and filter the air around them, while waste is expelled through the mouth. It is widely accepted that they do not have lungs, so this is possible, and yet implausible because Runners, or Dog Aliens, don't have them. But it may be that the Runners have lungs.
* The spines might be used as a defense mechanism, to repel enemies that try to sneak up on them from behind or above.
* They might also be traits that the alien acquires by chance when developing inside the facehugger, putting legs of the facehugger on the back. The chestbuster does not develop directly from the facehugger (instead, the facehugger plants the egg/larva that will become the chestbuster inside a host), but it's not impossible that it acquires genetic traits from it.
* They might be used to blend in with the hive web when under attack.
* The spines may be for Chestbursters to latch onto, allowing the adult to bring them to a safer location.
* If the alien uses echolocation to see its prey, these may be what they feel the vibrations from.
* They may be used to carry unhatched eggs to a new location when the Queen dies giving them the ability to still climb walls while on the move.
* They might be used to create the hive somehow.
* The spines may be used to distribute pheromones - to distinguish one from another, and from other hives.
* The spines may act much like the Carrier Xenomorph form seen in Alien Vs. Predator: Extinction, allowing a Facehugger to hook their spider-like legs until a victim is near. The Facehugger will let go of its crude form of transportation, find the victim, and proceed with the process of laying eggs.

### Secondary Jaws

The secondary jaws, also known as the inner mouth, double jaw, or maw, is another disturbing feature of the species. It's assumed that it's powered by extremely strong muscles inside the creature's head, that enable it to be quickly launched and retracted, similar to the tongue of a chameleon.

It is the Xenomorph's close-combat weapon, as opposed to its long-range tail. The Xenomorph lashes it out of its mouth, and it destroys anything it hits, able to put a hole in a thickened Yautja skull and still have enough power to plunge another hole through the back as it escapes.

The secondary jaw is powered by muscles as seen in the first Alien vs. Predator movie when the predator rubs a part of the interior (resembling the gills of a crab) a feature that can be seen from the external midsection on each side of the head, ovular in shape. Muscles rub along here, letting the mouth be pushed out like a piston through the target the Xenomorph has acquired.

The Predalien has the ability to use its inner mouth to implant Chestburster embryos into a host's throat, like a Facehugger.

Yautja take them as souvenirs of their kill.

### The Tail

It is accepted that the tail is an offensive weapon and little more. Though the creature can and will run on all four appendages, it often stands on its two hind legs so it can reach for its prey with its arms. While standing, it has also been seen to impale its victim with its tail, even to the point where it can raise a creature heavier than itself to eye level (if it had eyes), possibly in preparation for a face-bite using the secondary jaws. This would clearly be impossible if the tail were needed for balance, as the already-shifting weight would be too awkward, causing the monster to fall.

As a weapon, the tail is extremely efficient, as it is long enough to attack from great distance and can be used in a variety of ways; for example, in Alien vs. Predator, a Xenomorph used its tail to knock the legs out from under a Yautja before trying to stab it.

The tail can be used in stealth attacks, since it is flexible enough to attack from a variety of positions, and is hard to notice if it is behind the enemy, or if the area is rather dark. Even when the sharp point is cut off, the tail is still deadly, as the Xenomorph can use the tail to spray its acid blood from the severed tip over a wide area. Xenomorphs are also capable of using their tails as blunt-force weapons, clubbing their enemies with the vicious tail spikes.

### Acidic Blood

The body fluid of all Xenomorphs appears to be a highly concentrated acid. It is mistakenly called "acid blood", but when it is compared to the blood of every other known life form, it doesn't seem to carry any nutrients through the body.

It is also highly unlikely that it carries oxygen for a few reasons: the first being that the Xenomorph has been known to survive in vacuums such as space (for short periods of time, at least). The second being that, in the Director's Cut of Aliens, Bishop mentions that the fluid loses its acidity shortly after the creature's death due to oxidation. This is plausibly unimportant as oxidation is a term in chemistry used for the loss of electrons rather than a reaction with oxygen. All acids are oxidized no matter what they react with, therefore this has no bearing on blood carrying oxygen.

The "acidic blood" is able to spread through almost everything except the Xenomorph's body, as shown in Alien vs. Predator. It apparently knows how corrosive its "blood" is, as one flicked it at a charging Predator, and it has been used to escape cages (by killing a "brother"). Some specially-treated Predator weapons can resist this acid, although how long exactly is unknown. "On the pH scale, it would probably rank at a devastating negative four or lower", a previous author claimed.

This, however, is impossible, because the pH is the minus logarithm of the free H-ions' concentration, and thus can never be lower than -2.5 or so. Super acids with higher H-concentrations than this are merely theoretical, and cannot remain in this state because they immediately react and lose their unstable energy, by oxidation or neutralization. Another possibility is the presence of catalyst or enzymes in the blood which would increase the rate of reaction. However, we are limited in our knowledge of universal biology, as we simply base it off of what we know on Earth. Different environments in other worlds could evolve "acid blood" that could also carry whatever nutrients that the Xenomorph needs.

It has been often theorized that the Xenomorph "blood" may serve no function other than defense, being a liquid stored under the creature's skin that causes great harm to whoever succeeds in harming the Xenomorph. It remains possible, though, that the acid serves some function in the alien's metabolism, perhaps even as an actual blood system analolgue. One possibility is that it may be an extreme analogue of our stomach acid, and likewise serves to digest food. In that case, the Xenomorph digestive system would be spread like a circulatory system throughout its body: the acid is so powerful that anything it consumes is immediately dissolved and the remains distributed over its body, with the extremely resistant walls of the "acid vessels" somehow allowing nutrients to be absorbed.

### Genetic Adaptation

Due to transfer horizontal gene transfer during the gestation period, the Xenomorph 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.

Through experiments, it was discovered that the embryo attaches itself to a major artery of its host, to get nutrients as it grows. It is presumed that the DNA from the blood it acquires infuses itself with the embryo's DNA to make up for its lack of genetic structure.

It may take on a thicker, bipedal form with a darker exoskeleton if it comes from something that stands on two legs, such as a human. In the movie Alien 3, it came from a four-legged animal, and thus took on a more slender, sleeker appearance where it too moves as a quadruped, with a more reddish/orange exoskeleton. It may also take on some facial features of its host (such as mandibles when implanted in a Yautja). Predaliens (Yautja-Xenomorph hybrid offspring) have a yellow-green partial skin covering their exoskeletons.

Furthermore, it is conceivable that it derives some level of intellect from its host. The quadrupedal variant in Alien 3 seemed easier to trick than previous bipedal versions and the Predalien appeared to have a better understanding of weapons being used against it.

## Characteristics

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.

### Anatomy

The Xenomorph Warrior is equipped to be the perfect killing machine. It possesses an exoskeleton much like that of a lobster, impenetrable to everything but the most powerful human firearms (12-gauge shotguns, Pulse Rifles, and stanchion launchers are quite effective). Ash claims the creature's skin is made from 'protein polysaccharides', so this would imply a substance similar to chitin. He also says the creature replaces its surface cells with polarized silicone, which is a very inert, heat resistant, and flexible polymer. This allows the creature great environmental resistance. However, they are vulnerable to sudden, massive changes in temperature, as shown in Alien 3, when the creature is destroyed by first immersion in molten lead and then sudden cooling with fire sprinklers, causing its silicone shell to shatter.

Attached at the ends of both of its arms are a set of long fingers and shiny, black, and extremely sharp claws capable of slashing through almost anything within its grasp. It has two pairs of finger-like digits and appears to have two opposable thumbs (on opposite sides of the hand) on each hand. Its tail is long, and can be used as a whip. Later movies show it to have ridges on top, and a serrated toxic tip at the end to lacerate enemies.

It stands around 7 feet tall, averaging in at anywhere between 140 kg and 180 kg; although size may vary wildly depending on the host chosen, as seen for instance with the "Jock-Xenomorph". Its mouth is filled with sharp teeth, but its main killing device is the inner jaw that shoots out to penetrate the victim's brain.

The inner jaw (also known as an "attack tongue") is a muscular appendage on the inside of the Xenomorph's mouth. All Xenomorphs have this trait. It consists of a cord of muscle with a small but extremely deadly mouth-like appendage on the end. This attack tongue is able to punch through almost anything, from bone to Predator armor.

### Appearances

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 have a skeletal, biomechanical appearance and are usually colored in muted shades of black, blue or bronze. Whatever the host organism, they invariably possess distinctive, elongated, cylindrical skulls, but possess 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 creatures or Drones possess the smoother, domed carapace, while older specimens, such as Warriors, 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 tubes 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 centre below the base of the head. The exactly purpose of these tubes is unclear.

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.

### Physical Abilities

The adult Xenomorph is a living weapon, noted for its ferocity and deadliness in any condition. Once fully matured, they have great physical strength and agility. They are masters of stealth; a favored method of acquiring prey is to wait in a dormant state until an appropriate victim strays near, and then drop down silently from behind or use its tail to impale whoever walks by. The prey is generally blind to the fact that a Xenomorph is present, due to its propensity to camouflage itself within its nest walls or the surrounding artificial environment given its biomechanical-like appearance. A Xenomorph will also use its pitch black carapace to its advantage, lurking in the shadows whilst waiting for prey to stray too close.

Xenomorphs are shown to be able to take extreme amounts of physical damage that would kill any Earth lifeform. An example of this is the Queen in Aliens survived a multi ton exo-suit falling on her from over 30 feet. Xenomorphs are capable of surviving with limbs shot off as seen in AVP3 the game and Aliens. Even stabbings and shots through the head (though total decapitation kills them) as seen in Alien vs Predator and its sequel are not guaranteed to kill Xenomorphs.

Adult Xenomorphs are quick and agile, and can clamber along ceilings and walls, a skill they exhibit freely whether they are evading others, attacking, or hunting. They can survive in extreme temperatures, are well-adapted to swimming, can respirate in harsh atmospheres, and can survive in vacuum for short lengths of time. Their movement tends to be silent, and they do not radiate heat as their exoskeletal temperature matches the ambient temperature. They also salivate profusely. This saliva is not acidic, though some Xenomorphs do have the ability to spit acid, which may come from their stomachs, a special gland somewhere in their throats, or acid pouches lining the head. This can be used to blind victims, much like a spitting cobra.

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.

The creatures possess no visible eyes; Giger mandated this in his original design, because he felt that it made the creatures much more frightening if one could not tell they were looking at them. In the Alien vs. Predatorseries, the game implies that the Xenomorph sees using its attack tongue. In the original Alien film, the top of the creature's head was semi-transparent, with empty eye sockets of human appearance visible within. This element was dropped in later movies, but reused for the Predalien design, on the front portion of its skull.

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. One Alien on Fiorina 161 was even known to survive several tons of molten lead being poured onto it.

In Aliens, the adult creatures are lacking the smooth carapace covering their heads. 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 Xenomorph. This maturation process involves the now adult Xenomorph shedding the smooth dome-like plate covering its head, leaving the skin underneath to be exposed. In Alien³, a fish-eye lens (which creates a perspective similar to that of a peephole) was used to depict the Xenomorph's sight. Whether this can be considered sight or just a filmed representation of the creatures' sensory perception is unknown.

Xenomorphs may be able to detect their 'prey' through electro-reception. This is the method sharks use to detect even the most hidden prey. Creatures with the electro-reception sense can detect the electromagnetic field all animals produce allowing them to detect the creature's heart beat. This would explain how Xenomorphs always know where the humans are.

And, as depicted in the Aliens vs. Predator games, the Xenomorphs can also detect their prey using pheromones. Another theory is that the eyes of a Xenomorph are behind their black carapace and they see through it, similar to a one sided mirror (except in this case no one can see in, but the Xenomorph can see out).

Xenomorphs can also produce a thick, strong resin, which they use to build their hives and cocoon victims. Much like termites, they mix their viscous saliva with solids. It shows amazing heat and moisture-retaining qualities.

### Senses

Studies have shown that Xenomorphs possess sensory structures along the sides of their extended skulls that are capable of perceiving 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. The creatures are also capable of detecting heat via highly sensitive thermoreactive organs located behind the skull's frontal plate. Finally, the creatures possess largely vestigial photosensitive organs flanking the frontal plate; these visual receptors are thought to aid the creatures in seeing each other (Xenomorphs produce no notable body heat, a fact that would otherwise render them blind to their thermal receptors). These remnant visual organs are also thought to grant the creature the necessary depth perception required when attacking prey.

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.

### Cocooning

Cocooning is a trait used by Xenomorphs to reproduce quickly. An injured (but alive) human, or any other creature, is dragged away, and a cocoon of saliva and resin is placed over them (their face left free), usually in an area where the Queen has produced a large quantity of eggs, so that the Facehuggers are able to latch onto them easily and deposit a Xenomorph larva in their chest. In a cut scene in Alien (included in the Special Edition), Ripley found two of her cocooned colleagues actually being turned into Xenomorph eggs.

This suggests that Xenomorphs can convert humans into eggs when there is no queen, although this may have been scrapped as many other features of the Xenomorphs were in later movies (such as the transparent skulls and empty eye sockets). In the book, it's described how the drones are able to implant a fetus in up to four hosts, thereby creating enough drones and warriors to start a hive off.

Another feature of cocooning as seen in the game Aliens Vs. Predator 3 is that the Xenomorph Number Six, after entering and cocooning its victims, can change its appearance, eventually becoming a queen itself. This rapid genetic regeneration is also another evolutionary trait of the Xenomorph to ensure its very survival as a species. In Alien vs. Predators: Extinction the praetorian acted as a princess of the hive who then became the queen. This stage is seen with Number Six. If this is so, then Hudson is correct with them being like bees.

The Xenomorph Queen can lay specialized eggs that are bigger (like queen egg cells in bees which are bigger than drone cells) that upon hatching can carry on the species through making other hives after the new female cocoons into a queen, as seen with Number Six and the aliens of Aliens vs. Predators: Extinction. If this is the case though, that a drone can become a queen when no queen is present, then cocooning is also a method of survival for the Xenomorph species.

### Intelligence, Communication and Behavior

Xenomorphs appear to possess an intelligence roughly similar to that of a typical primate. Although they do not demonstrate Human-level intelligence as a species (such as abstract reasoning, introspection, and technological advancement), their queen appears to possess considerable acumen in its social behavior and manipulation of human technology, such as cutting the power of the LV-426 colony and operating an elevator. In the director's commentary for Aliens, James Cameron noted that the Xenomorphs in Aliens had been alive far longer than the Xenomorph in the original, and so has had more time to learn how to manipulate machinery, if only at the most basic level. However, the genetic Xenomorphs from Alien: Resurrection learned very quickly that they were being contained, so they killed the weaker one so the acid of the Xenomorph's blood would seep through the floors.

As the adult Xenomorphs seem to inherit physical characteristics from their hosts (exemplified, for example, when a Yautja became infected, the parasite that later developed into a "predamorph" or "predalien") it is possible that the intelligence level of the creature may be influenced by its host as well. Furthermore, being a eusocial species, it is possible that the intellectual capacity varies for each different caste.

Xenomorphs have demonstrated little emotion, though they are not completely devoid of fear, especially for their eggs, or in the presence of fire. They have also been shown to exhibit pain through shrieks or screams when attacked.

The Xenomorph 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 maternal instincts toward their Eggs and the Queen.

In the Aliens literature, it has been suggested that the creatures may have a hive mind, or a collective consciousness directed by the Queen, who can call back and give orders to her warriors, telepathically and with shrieks. In the Aliens comic book series, as well some novelizations (produced before the Alien³ film), it is suggested that the Queen Mother Xenomorph communicates telepathically with its potential hosts, through terrifying dreams and religious visions, leading to the formation of cults with the Xenomorph as a god-like figure. This is similar to the H. P. Lovecraft The Call of Cthulhu. This can be seen in Alien 3, when Golic is induced by supposed "telepathic" messages from a captured Xenomorph. This ultimately leads him to release it and let it kill him. He called it "The Dragon", and viewed it as a god.

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 pheromone release, ultrasound or even some form of telepathy. 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. According to some sources, 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.

Through cloning in the events surrounding Alien: Resurrection (noted in the novelization), it appears that the Xenomorphs' hive mind includes a collective memory that passes along even at a genetic level. Through the tests conducted on Ellen Ripley, it is revealed that the memory passed from Ripley onto the new generation of Xenomorphs allows them to read and understand different languages. Events on the LV-426 colony and the USM Auriga show that the species excels at observational learning. Another case of observational learning from Alien: Resurrection is seen, after a Xenomorph has escaped its cell. It had learnt that the consequences of attacking the glass through which they were watched was a jet of extreme cold (possibly liquid nitrogen), triggered by a large red button on the console. When a crewman enters the now-empty cell to study the hole through which the Xenomorphs escaped, one of them enters the control room and activates the button using its inner jaw.

In the rare event that a Xenomorph finds itself under attack or otherwise vulnerable, it might display incredible creativity and cleverness. They are capable of moving quickly and silently in ventilation systems, despite their size, and will use such conduits for ambush, escape, or simply as an easy way to travel between areas.

Xenomorphs are conscious of the effects of their acidic blood, and will use it to their advantage - to break out of human-constructed confinement, or as a weapon. They show some military tactics (such as retreating when overwhelmed), and can find ways to get around certain problems (such as pushing the red button to freeze a soldier in liquid nitrogen). They know that the darkness is their ally, and break lights to create cover.

### Blood and Secretions

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, 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 hydrofluric acid, which was used against them to great effect on LV-178.

Xenomorphs 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.