|Biochemistry||Silicon-based lifeform (presumed)|
|Average Height||Varies by caste|
|Average Weight||Varies by caste|
|Average Length||Varies by caste|
|Average Wingspan||Varies by caste|
|Predators||Yautja (sports hunting)|
|Capital City||Xenomorph Prime|
The Xenomorph XX121, better known just as Xenomorphs (which literally translates to "strange form") or simply Aliens, are an extraterrestrial, endoparasitoid species with multiple life cycles, possibly originating from the planet Proteus (also known as Xenomorph Prime). One of the most deadly of all known alien species, these creatures need a host organism in order to reproduce. The appearance of the Xenomorph varies depending on its host, as they leech DNA from their host to speed up their maturation process. The seemingly common 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 this species is generally twice as large (they can grow even larger, some even up to 100 feet tall, and stronger if given time) 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").
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 humanity has available, 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.
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, but apparently it went horribly wrong. As a result, over the years the Xenomorph has become an entirely new species in the galaxy. Despite this, the crew of the Prometheus encountered cannisters on a Mala'kak vessel filled with an unknown substance that resembles the royal jelly secretions of Xenomorph hives. This substance mutated harmless organisms into somewhat hostile creatures. When humans became "infected" with this substance, hormones are released that cause them to mate with one another. This very quickly produces a different subspecies of "octo-facehuggers" that can grow incredibly large. This new subspecies regardless of who it infected, will result in the "Deacon" or Proto-alien. It is not known what new subspecies would result if the "octo-facehugger" impregnated a Yautja.
Another theory is that 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). Without their native ecosystem to keep them in check, they have since 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 gathering them, as happened with another severely dangerous xenomorphic species, the Metroids. The Mala'kak, the Yautja, Humans, and an unspecified highly technological humanoid species began using them as means of sport, terraforming mechanism, as biological weapons, food delicacies, and scientific experiments.
One interesting idea though, is that they were brought over by the Mala'kak as biological weapons against an unknown threat (such as the Yautja species) or a weapon to wipe out humanity and other species that exist in the galaxy. The eggs at the derelict ship found at LV-426 was in fact a biological weapon that turned against the crew. The LV-426 incident allowed humans to take more notice into account about the Xenomorphs that they do know exist in the galaxy.
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 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 lifeform 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, which then grows very quickly, developing into the adult Xenomorph.
Although 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 eyeless head, 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. Despite this, it is known that their teeth and claws are metal, indicating that they may in fact be some sort of carbon/silicon hybrid.
Xenomorphs appear to possess an intellect roughly similar to that of a typical primate, but have shown to learn relatively fast and utilizing the situation around their environment. 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.
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 or direct malice, especially in relation for their eggs, or in the presence of fire. They have also been shown to exhibit pain through shrieks or screams when attacked. They seem to be naturally flamboyant, and burn longer than a compared species.
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. It has also been 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 Cthulhu cults, such as when Golic is induced by supposed "telepathic" messages from a captured Xenomorph. This ultimately led him to releasing it and letting it kill him. He called it "The Dragon", and viewed it as a god.
Through cloning 300 years after the LV-426 Incident, 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 was discovered 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 showed that the species excels at observational learning. Another case of observational learning has been reported, occurring after a Xenomorph had escaped its imprisonment. 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 will break lights to create cover.
The Xenomorph Warrior is equipped to be the perfect killing machine. It possesses an exoskeleton much like that of a , impenetrable to everything but the most powerful human firearms (12-gauge shotguns, Pulse Rifles, and stanchion launchers are quite effective), though the exact weaknesses may vary between castes. The Weyland-Yutani android Ash claimed the creature's "skin" is made from 'protein polysaccharides', so this would imply a substance similar to chitin. He also stated that 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 occurred when Ripley fought one of the creatures and successfully 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, giving it six phalanges per hand. Its tail is long and very prehensile, and can be used as a whip or better yet, a spear. It appears that the variable DNA of hosts such as Humans affects the exact morphology of a hive, likely stemming from the host of the Queen. This has been shown in that each encounter with Xenomorphs has been different, and tails have been a somewhat obvious difference, with some showing ridges along the dorsal ridge, as well as a serrated, toxic tip at its end used to lacerate foes.
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 at swift speeds 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 post-chestburster 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.
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 bio-mechanical-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 known Earth lifeform. An example of this is when the Hadley's Hope Queen survived a multi ton exo-suit falling on her from over 30 feet. Xenomorphs are capable of surviving with dismembered limbs, with this trait going so far as barely slowing down their overall speed and agility. Even stabbings and shots through the head are not guaranteed to kill Xenomorphs, though total decapitation is absolutely fatal to their kind, cutting off brain activity as with typical lifeforms.
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 it is extremely thick, slimy and sticky. 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.
The creatures possess no visible eyes, and in fact does not need them, instead seeing aural sight. Strangely, it has been implied that the Xenomorph sees using its attack tongue. In some variants of the species such as Kane's Son, the top of the creature's head may appear semi-transparent, with empty eye sockets of human appearance visible within. This appears to be due to their maturation process, with the carapace covering the heads losing its smooth qualities. This maturation process involves the now adult Xenomorph shedding the smooth dome-like plate covering its head, leaving the skin underneath to be exposed.
The creature aboard the Nostromo, Kane's Son, was at one point held mesmerized by a spinning green light for several minutes. Due to the absence of clearly visible eyes, it is possible that the creature uses echolocation to see its environment, much like bats. It may be for this reason that Xenomorphs hiss almost constantly. Though it may have the ability to see through an unknown structure, as they evolved differently from life on Earth.
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.
Also 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). Some species of terrestrial fish such as the Barreleyes see through a transparent layer of skin; it is possible Xenomorph vision is similar.
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.
""Buggers don't like fire. This'll flush 'em out"."
Xenomorphs, in all stages of their life cycles, have been said to have vulnerabilities to heat; the only known Xenomorph variant not vulnerable to fire is the #Predalien. This seems to be due to it secreting a fire-retardant layer over their body which cannot be ignited, though they are visibly pained by temperature extremes such as liquid nitrogen.
A rapid succession of extremes in both high and low temperatures apparently causes a thermal shock effect on a Xenomorph's exoskeleton. Xenomorphs are capable of adapting themselves to cold environments with little discomfort. The alien queen is extremely vulnerable to fire, for unknown reasons, as are Bull Aliens.
Xenomorphs are shown to be both invulnerable and vulnerable to small firearms, ranging from 9mm to 5.56mm. Evidence from Hadley's Hope marines Vasquez and Lt. Gorman revealed that when they found themselves trapped in the ventilation between advancing aliens coming from both directions, Gorman fired with his pistol on one of them with no effect at all, instead it looks like they bounce off (presumably from the head carapace). Vasquez had earlier also held an alien at gun point and fired her pistol at the head, which apparently goes through and the alien rattles away, obviously damaged. High-caliber firearms, with the explosive rounds of a M41A pulse rifle may cause the creatures to detonate. High-energy beam weapons, such as the plasma weapons used by Yautja, appear to be the best way to kill the Xenomorphs.
They are not invulnerable to melee weapons, although such equipment is likely to be destroyed upon contact with their acidic blood, with a few notable exceptions. It also leaves the user in close proximity to the alien's blood, which is in all cases an extremely dangerous venture.
Cocooning is a trait used by Xenomorphs to reproduce quickly. A human, or any other creature, if dragged away, would have a cocoon of saliva and resin placed over them (their face left free, perhaps for respirative purposes or for hopefully attracting other would-be victims with their potential moans and cries for help), 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.
Another feature of cocooning involved the xenomorphs themselves: After entering and cocooning its victims, they can change their appearance, eventually becoming a queen itself, although this may require making physical contact with royal jelly from a former queen. This rapid genetic regeneration is also another evolutionary trait of the Xenomorph to ensure its very survival as a species. Praetorians can act as a princess of the hive to become a queen. 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. 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 and helps prove how difficult it is to actually eradicate a xenomorph infestation.
The Xenomorph have been reported. This is because the Xenomorph's form is at least partially affected by its host, so that different species of hosts will create different varieties of Xenomorph. for instance, when a dog or an ox spawns a Xenomorph, it will have a distinct canine body structure, quadrupedal movement, and greatly enhanced speed, known as a Runner.
Regularly, Xenomorphs are depicted as tall, slender creatures with a roughly human biomechanical design. The chest area appears to be rib cage-like in design.
However, other groups such as those spawned from the hidden temple in Antarctica and those found many centuries later, they are depicted as being shorter and bulkier organisms, as well as being more quadrupedal.
These differences is what differentiates the younger Drone and the older Warrior castes. The Drones (used as 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.
Xenomorphs have six fingers, with the index and middle fingers conjoined into one digit, ring and little fingers also conjoined, and thumbs on both sides. Despite this, those Hadley's Hope individuals only have five fingers, with the second thumb missing. This may be a mutation effect from that particular hive, or may indicate that the lose their second thumb at some point during maturation.
Xenomorphs are normally plantigrade, though Runner Xenomorphs are digitigrade, owing to its quadrupedal host organism. In stark contrast, much later Xenomorphs have similarly digitigrade hind legs set up in a manner that does not conform with the appearance of previously-seen members of the breed. This is complicated by the fact that these Xenomorphs were spawned by a Queen grown from cells derived from a clone of Ripley, making their genetic heritage muddled at best. This could mean it was a simple huge mutation.
In some specimens, their legs are sleeker and more skeletal in appearance.
The tail is a huge variation between the various hive infestations reported. In some, it was roughly the length of the rest of the body, making up a third of their overall length and possessing a small, almost surgical stinger-like barb on the end; however in other specimens the tail is extended in length and features a large, knife-like blade at the tip. In some members, the tails have also supported a ridge of spikes right before the blade, which appears to help some breeds swim better. Their tails are known to reach a full body length in and of itself.
Reports exist that indicate that if "stung" by a Xenomorph's stinger, the barb can sometimes remain lodged in the victim.
The most notable feature of the Xenomorph species is the elongated, banana-shaped head. Though it appears to lack any sort of optical vision components (such as eyes), it is known to at least "see" by sensing pheromones and/or auras. Interestingly, a Drone will not kill a host body already infected, or at least when infected with a Queenburster. 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.
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 compound eye, but there is absolutely no proof of this.
Despite this, the Xenomorphs could theoretically see. Certain specimens have shown an actual, physical, humanoid skull built under the smooth carapace, with the smooth top working like a one-way visor.
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.
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 it has been said that the dorsal spines may be used to secrete and possibly store the resin used to build their hives, assuming that it does not stem from their saliva.
Xenomorph Drones have been known to bury themselves in the ground, yet their spines will still just break the surface, implying some use when connected to the environment. This may be either biological (breathing, heat exchange, et cetera) or sensory (detecting the vibrations of potential prey items 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, 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.
The secondary jaws, also known as the inner mouth, double jaw, or maw, is another disturbing feature of the species. It's assumed that its 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. These muscles may make up a large portion of their head.
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 when a 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 have been known to take them as souvenirs of their kill.
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, one 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.
The body fluid of all Xenomorphs is a form of 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 the Weyland-Yutani android Bishop mentioned 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 Yautja, and it has been used to escape cages (by killing a "sister"). Some specially-treated Predator weapons can resist this acid, although for how long exactly is unknown. "On the pH scale, it would probably rank at a devastatingly negative four or lower".
This is theoretically possible, despite the fact that pH is the minus logarithm of the free H-ions' concentration. To put this this into perspective water has a neutral pH of 7 and Human stomach acid has a pH of 1, which would lie at the very bottom of the 1 to 14 scale. Attempts to discredit such a claim are challenged indirectly by chemists who have found that mixing antimony pentafluoride with hydrofluroic acid can produce a solution with a pH of -31. This therefore would render it 100,000 billion, billion, billion times more potent than stomach acid. It should be noted however that this acid is basically formed by mixing two incredibly strong acids together in the first place, which interact to become even more acidic. Though former theories have in fact stated that two potent chemicals (with perhaps some biological catalyst) may mix to create the acidic blood seen. Perhaps the strongest 'solo' acid would be the boron-based carborane with a pH of -18. Yet due to the structure of Carborane, the H+ ions, which create the phenomenon known as acidity, are shared so efficiently between molecules that it would have no corrosive effects at all. Hence despite challenges It would appear even that which is known on earth certainly leaves scope for the incredible properties of the aliens acidic blood. It may also go without saying that 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 analogue. 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.
Due to 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. On Fiorina "Fury" 161, 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 on Fiorina 161 seemed easier to trick than previous bipedal versions and the Predalien appeared to have a better understanding of weapons being used against it.