Xenomorph


 * Alien redirects here. For extraterrestrial species in general, please go to Category:Alien Species

The Xenomorph is a pseudo-parasitic lifeform with a multi-staged life cycle native to the mysterious planet of Xenomorph Prime.

The appearance of the Xenomorph varies depending on its parent host. The human phenotype is generally around 7'2", and roughly 136.0 to 181.4 kg with a long muscular tail and large oblong head.

History
There is not one solid fact as to the origins of the Xenomorph species; instead, there are many assumptions, which can neither be confirmed nor denied.

The most commonly accepted hypothesis is that they evolved naturally on a planet much different than our own.

Other ideas include that they were created by another race, perhaps the Yautja (Predator) as an "ultimate prey", or by a race only to known to us as "Space Jockeys", as a biological weapon. Xenomorphs are specifically said to not be indigenous to LV-426, a relatively small and unknown planet, where a large body of their eggs were found in the hold of a derelict Space Jockey ship. No one knows if they were using the eggs as research, or as a bioweapon. Some say that billions of years ago, the advanced race controlled much of the universe with the xenomorphs, but were wiped out by them.

Vulnerabilities
Xenomorphs, in all stages of their life cycles, have been said to have vulnerabilities to heat, although this was only shown in a deleted scene from the Alien Special Edition DVD, in which Ripley searches for her missing shipmates in the bowels of what appears to be the engine/boiler room of the Nostromo.

The only xenomorphs not vulnerable to fire are the Predaliens. In the game Alien vs. Predator: Extinction, they secrete a layer over their body, and with that layer cannot be caught on fire, though they are visibly pained by 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.

Xenomorphs are shown to be vulnerable to close-range small firearms, ranging from 9mm to 5.56mm, and high-calibre firearms, with the explosive rounds of a M41A pulse rifle causing the creatures to detonate.

High-energy beam weapons, such as plasma weapons, appear to be the best way to kill or destroy the xenomorphs.

They are not invulnerable to melee weapons, although such equipment is likely to be destroyed upon contact with it's acidic blood, with the few notable exceptions of some.

In the game Predator: Concrete Jungle, they can be paralyzed for a short period of time with sonic or pulse traps, and the Predator combistick can be used to kill the xenomorphs without cutting them.

Intelligence
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 had more time to learn how to manipulate machinery, if only at the most basic level.

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

In the Aliens literature, it has been suggested that the creatures 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 it's 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 cult in H. P. Lovecraft's 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.

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.

In the rare event that a xenomorph finds itself under attack or otherwise vulnerable, it displays 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.

Physical abilities
The adult Xenomorph is a living weapon, noted for it's 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. 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 it's biomechanical appearance.

Adult xenomorphs are quick and agile, and can run 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 or a special gland somewhere in their throats. This can be used to blind victims, much like a spitting cobra.

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 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.

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. In Alien³, a fisheye 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.

However, in the novelization of the movie Alien, the creature is 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. In the 2010 Alien vs. Predator game, it is mentioned on one of the Marine audio tapes that Xenomorphs have vision.

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 creatures 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 detect their prey using pheromones.

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.

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 xeno egg in their chest. In a cut scene in Alien (included in the Special Edition), Ripley found two of her cocooned colleagues had been metamorphising into Xenomorph eggs, which suggests that if there is no Queen, the coccoon can also change captured subjects into new Xenomorph eggs.

Anatomy
The Xenomorph Drone is equipped to be the perfect killing machine. It dons 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).

Attached at the ends of both of its arms are a set of long fingers and shiny black claws capable of slashing through some types of metal (as seen in ALIEN books, such as Book 2: Nightmare Asylum). 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 sting prey.

It stands around 7 feet tall, averaging in at anywhere between 140 kg and 180kg. Its mouth is filled with sharp teeth, but its main killing device is the inner mouth that shoots out to penetrate the victim's brain.

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 suggested, 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 and quadrupedal movement.

It is also possible that there are breeds of Xenomorph that are not directly related.

Upper Body
In the original Alien film, and in the sequel Aliens, xenomorphs are depicted as tall, slender creatures with a roughly human biomechanical 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, but this is, of course, non-canon.

In the movie, there are only two castes of aliens: Queens, and Drones/Warriors. The Drones and Warriors may have different tasks: Some defend the hive, and others hunt potential hosts, while some live only to protect the queen.

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.

The chest area appears to be rib cage-like in design.

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 may be a phallic symbol. 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 lacks 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).

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-in. In Alien 3 the a fish-eye lens represented the Runner Alien'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 are a series of appendages that appear to have no function. It's still in debate what they are used for.

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:


 * These creatures have come from a mainly amphibious planet, and perhaps the spines are a mechanism to swim underwater faster to catch prey.
 * The spines are spiracles that take in and filter the air around it, while waste is expelled through the mouth. It is widely accepted that they do not have lungs, so this is possible, and yet impossible because Runners, or Dog Aliens, don't have them. But it may be that the Runners have lungs.
 * The spines are used as a defense mechanism, to repel enemies that try to sneak up on it.
 * The spines are for Chestbursters to latch onto, allowing the adult to bring them to a safer location.
 * The spines are used to distribute pheromones - to distinguish one from another, and from other hives.
 * The spines act much like the Carrier 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.
 * Not widely accepted: Because the creature has an exoskeleton, it is unable to release body heat built up while chasing prey. To compensate for this, the spines act as a ventilation system, keeping it from inadvertently killing itself. However, the Runner does not have these, and its breed is the fastest, therefore exerting the most energy. Yet it appears unfazed.
 * Not widely accepted: The spines were once wings (like a dragonfly's) that evolved off, leaving these odd structures. Or, they are slowly evolving into wings.

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 monster's head.

It is the Xenomorph's close-combat weapon, as opposed 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 inertia to plunge another hole through the back as it escapes.

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 has 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 it 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.

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). And 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.

The "acidic blood" is able to eat through 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. 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.

Genetic Adaptation
Adult Xenomorphs have been known to take on traits of their host. How exactly this is done is not understood.

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 Predator). Predaliens (Yautja-Xenomorph hybrid offsprings) have a yellow-green partial skin covering their exoskeletons.

Egg
The Xenomorph is born in egg form, laid in place by the hive's Queen, through the use of a detachable ovipositor. The egg is thick and gelatinous, usually with several membranes attached to the outer layers. It can take nutrients from the ground to support the creature inside.

The Xenomorph hatchling - called a Facehugger - is protected by a thick fleshy layer at the top of the egg, where the "shell" peels open when the Facehugger senses creatures nearby.

In the first movie, it appeared they could sense when another creature crossed into some form of mist covering their nursery area. It's a widely accepted hypothesis that this was a containment field to keep the eggs dormant, put in place by a Space Jockey. When this mist was broken, the Facehuggers appeared to be alerted, and went on the search for the host.

Facehugger
After the egg opens, the Facehugger emerges and seeks out a nearby life form, latching onto its face, wrapping its tail around its airway, and implanting the xenomorph embryo(s).

It will coil its tail tighter around the airway to prevent premature removal, and an attempt to sever the fingers found that Facehuggers possess the same acidic blood as a Xenomorph.

The Facehugger supplies oxygen to keep the host alive during the impregnating process. Once the embryo(s) has been implanted, the Facehugger falls off, curls up, and dies.

Hosts usually fall into a short coma and wake up ravenously hungry. Hours might pass between then and their time of death. Predators have the longest time to live, it takes longer than other Xenomorphs because the chestburster needs more time to get all the details that are needed for the Predalien.

However, in some cases, they will awake not gradually but suddenly - just in time to be conscious for the Chestburster's push out into the world. Their state of normalcy will last only seconds or minutes.

It was also proven - in the movie Alien - that when a host awakens, there is some sort of a memory lapse before the Facehugger actually attaches itself to the host; they don't remember anything that has happened to them.

Chestburster
After attaching itself to a vein and gestating in the chest cavity, Xenomorph infants - called Chestbursters - writhe and chew through the host's chest, causing severe pain, blood loss, and shock. The host's rib cage is cracked open, bones bent outward. No one has survived this process, though Ripley in the film Alien: Resurrection was cryogenically frozen after she was cloned, and then had it surgically removed.

At this stage, the Xenomorph is small, limb-less, and very vulnerable. Among other possibilities, its neck can be snapped. It needs to get to a safe area so it can reach its next life stage. It moves with its long tail, and can coil up and jump. It cannot climb on walls or ceilings.

In Alien vs Predator: Extinction, they turn into a cocoon (though this could be a subspecies).

Adult
Little is known about the transformation that occurs between the Chestburster and Adult phases.

The Xenomorph appears to moult before reaching maturity. Maturity is reached in a few hours, and involves a dozenfold increase in mass, which would presumably require some form of nourishment. In the novelization of the movie Alien, Ripley comes across a food locker that had been raided, apparently by the Xenomorph to get food. Whether or not this was nourishment to grow was not specified. In the video game Alien Vs. Predator 2, one of the Alien missions requires the player to find a source of food in order for the Chestburster to advance to it's Drone phase. At the end of the level, a short cutscene indicates that the Chestburster consumes a house cat in a carrier. The scene does not show what happens during the change in life cycle.

In Alien, Kane found a shed skin resembling a Chestburster in the area of the Nostromo it had taken shelter in, inferring that it sheds its skin before moving onto its next form. This has also been shown in the expanded universe.

When the first Drone encountered on record was born on the Nostromo, it had a smooth, long head, and an upright-standing body. It had no eyes, a tail, and strange spines protruding from its back.

However, many years later on LV-426, the same warriors were found, but they looked slightly different. The head was no longer smooth, but ridged. One theory is that the smooth-headed Xenomorph was a Drone, and the ridge-headed Xenomorphs were Warriors. (The Xenomorph in the first movie built a nest. Only Drones can build a nest - that is their job in the colony.)

The most widely accepted idea is age - the Xenomorphs found on LV-426 were more than a few days old, where all of the others encountered were less than a day old. On the other hand, the Alien vs Predator game has showed that the Drones are black (like in the movies), but the Warriors are a very dark blue, the color difference indicating that age is not a factor.

Another variation is the Dog or Runner Xenomorph, called so because of it's dog-like stance (standing and moving on all fours) and higher speed. It's host was a dog, rather than a human.

Another variation was encountered on an expedition to Antarctica. These warriors were less humanoid and sometimes walked on all fours. Their tails were longer, with a large, curved barb at the end. The head was smooth, but much shorter than normal. It is important to note, however, that this particular Xenomorph hive was grown by the Predators, who introduced a hormone with unknown effects into the Queen's system.

Xenomorph Caste System
The Xenomorphs have a caste system similar to those of bees and ants. A major difference is that their caste system is far more complex, and divided into two main groups by sex.

Drone / Female Xenomorph
The basis of any Xenomorph hive; the Drones (female Xenomorphs) are very much like worker bees or ants. Their main tasks are to keep the hive in good condition and protect it from attackers.

The Queen secretes hormones that keep them sterile, and when she dies, the Drones go into a rage, fighting with each other until they find the strongest among them. That Drone will then evolve into a Queen and immediately begin to lay eggs. She will also choose whether to keep the Praetorian consorts of her predecessor, or choose a new pair of Warriors for the role.

They average in size at about 6-7 feet tall standing on hind legs, and about 14-15 feet long, tail included. They have the basic body build of the Warrior, except that their dome is completely smooth, whereas the Warrior's dome is more ridged. Drones are smaller and somewhat more delicate than the Warriors, not considered quite as dangerous by Yautja standards, but striking fear into the heart of any human.

Like all of their brethren, they have acid blood, but only the Drone can spit this secretion onto prey over a short distance.

Drones have an organ in their body that releases a sticky fluid that they can spit out of their mouth onto any surface. It can be used to harvest hosts for the Queen's Facehuggers.

Warrior / Male Xenomorph
Warrior Xenomorphs - commonly known as simply the Warrior - are the soldiers and protectors of the hive. They are all male children of the hive's Queen, bigger and stronger than the Drones. The Drones are no less deadly, but somewhat less intimidating.

Warriors average in size at about 8 feet tall standing on hind legs, and about 14-16 feet long, tail included. In most cases, the Warrior looks the same as a Drone, except that the dome on top of the head is completely gone.

They evolve into Praetorians when the Queen wishes, serving as her consorts - usually two of them at a time, but sometimes three - when she wishes to watch them battle for her attentions.

Predalien
Like normal Xenomorphs, a Predalien gains traits from it's host. But from the Chestburster stage, it is noticeably different from other Xenomorphs. It is a somewhat dark shade of green with external mandibles, due to it's Predator (Yautja) heritage.

They lack speed, and their acid blood is not as deadly as a normal Xenomorph's. It will glow like a Predator's.

If a Predalien is part of a hive that has no Queen, it may serve as Queen due to it's reproductive capabilities - it's mandibles hold the host's head in place while it's inner mouth implants one or more Xenomorph embryos into the host's throat, similar to the function of a Facehugger. There may be up to five or six Xenomorph embryos planted per host, if the Predalien needs to build up numbers quickly.

Praetorian (Royal Guard)
Praetorians are bigger and stronger than the Warriors. Their primary role within the hive is to guard key locations of importance or interest, and, if nothing else, to protect the Queen herself. Most Praetorians can be found very close to the Queen's chambers.

The physical features of the Praetorian are pristine, and very similar to the Queen's: it has a crown-like head crest, large size, and great strength. In most references, a Praetorian is the last stage of a male Xenomorph's life cycle.

In Alien vs. Predator: Extinction, the Praetorian is said to be created by special eggs and Facehuggers. However, it is widely accepted that Praetorians evolve from the Warrior caste. The Queen selects a Warrior to become a Praetorian, and the Warrior is then attacked by fellow Xenomorphs from the same hive and banished. The Warrior must survive on its own for a long period of time. It grows and sheds, becoming approximately fifteen feet tall and gaining it's head crest. It returns to the hive as a worthy guard to the Queen.

Queen
The Queen is the largest and most intelligent Xenomorph in the hive. She lays many eggs that hatch to become the first stage of Xenomorph.

It is unclear whether the Queen engages in combat outside of protecting her hive. The Queen is usually nestled deep within the hive, protected by Warrior guards.

She has been known to display some logic-based intelligence, primarily in using simple human technology such as lifts. She is the most dangerous of the hive, displaying extreme aggression and using her intelligence to devastating effect.

When attached to her egg sac (ovipositor), she is immobile and vulnerable to attack. When she removes herself from it, however, she can move surprisingly fast. She attacks with her four clawed arms, as well as her long, bladed tail. She has also been shown to use her main and inner jaws in combat.

Interestingly enough, it seems that the size of Queens vary. In Aliens, the Queen was shown to be maybe only twice the size of a Drone. In AVP, she is shown to be considerably larger - three or four times the size of a Drone. This could be explained in a similar fashion to an older Drone's ridged head. The Queen in AVP was very old; although kept in a dormant state for long periods of time, she could have been alive for several millennia, or she could have been an Empress. Queens usually stand around 15 to 20 feet tall.

When there are no Queens within a certain hive mind range, a Drone will be produced in chestburster stage. After making a nest, the Drone will go through a hormonal change and become a Queen, producing an egg sac and eggs.

Empress
In the video game Aliens vs. Predator 2, there is mention of a Xenomorph Empress. Although very similar to a regular Queen, the Empress's main duty is to establish order on a planet with multiple hives. The only known differences between the two are their size (the Empress is substantially taller than a Queen, standing anywhere from 20 to 25 ft. tall), and the crown (an Empress's crown has five points instead of the traditional three).

It is possible that Dr. Eisenberg was merely using the term "Empress" to refer to the Queen. However, the Empress is bigger then the average Queen seen in the Predator and Marine missions.

It is also mentioned that after a hive grows to around 2,000 members, the younger Queens set out to establish new hives, and that if the Empress was to die, it would cause the younger Queens to fight over the new hive ruler. It's most likely that an "Empress" Xenomorph is merely a Queen that has dominated the other Queens in a hive. This would make the title "Empress" just that: a title.

Design
Though maintaining the basic design shown in the Aliens vs. Predator video games, numerous artistic liberties were taken in it's film portrayal. Or rather, would have been taken. One abandoned concept was to have the Predalien reproduce by injecting victims with "DNA acid" through it's tail, causing the victim to swell and explode.

Another, having the Predalien inherit it's host's tendency to skin victims. This was probably dropped because skinning victims isn't something that comes instinctively to Predators, but rather something that they learn.

Trivia

 * The Xenomorph's design has inspired the creation of the Metroid villain known as Ridley, which is a reference to Alien's director Ridley Scott.
 * A Xenomorph named Heinrich serves as the final boss of the Nintendo 64 game Conker's Bad Fur Day.

Related species

 * Space Jockey
 * Yautja

Xenomorph Castes

 * Drone (Alien)
 * Warrior Xenomorph
 * Runner
 * Praetorian
 * Carrier
 * Ravager Xenomorph
 * Queen
 * Queen Mother

Xenomorph Variants

 * Acid Alien
 * Arachnid Alien
 * Arachnoid
 * Bodyburster
 * Bull Alien
 * Chrysalis
 * Defender
 * Empress
 * Facehugger
 * Flying Xenomorph
 * Flying Queen
 * Gorilla Alien
 * Hive Warrior
 * Infectoid
 * Jock-Alien
 * K-Series
 * Killer Crab Alien
 * King Alien
 * Lead Drone
 * Leech
 * Mantis Alien
 * Newborn Xenomorph
 * Night Cougar Alien
 * Panther Alien
 * Predalien
 * Queen Facehugger
 * Razor Claw
 * Red Alien
 * Rhino Alien
 * Rogue Xenomorph
 * Snake Alien
 * Scorpion Alien
 * Smasher
 * Super-Evolution Xenomorph
 * Swimmer
 * Swarm Alien
 * Wild Boar Alien
 * Xenoborg
 * Badger Alien
 * Weasel Alien
 * Horse Alien
 * Vampire Squid Alien