Graphic showing the basic stages of the Xenomorph life cycle.

The life cycle of the species Xenomorph XX121 is a complex process involving several distinct stages and the use of a living host organism as a vessel inside which the infant Xenomorph gestates. The cycle, and in particular the use of hosts that invariably perish when the infant Chestburster forces its way through their ribcage, is often considered the species' signature aspect and is the characteristic for which they are most well known.

Note that this article is not a comprehensive list of all known Xenomorph castes, but merely lists the key stages in the creature's life cycle.


Xenomorph life cycle.png

The Xenomorph life cycle is comparable in many ways to certain parasitoidal insects found on Earth, such as the wasps of the Chalcidoidea and Ichneumonoidea families, which lay their eggs on live prey that are then consumed by the hatching larvae. However, the cycle is at the same time unique, particularly with regards to the manner in which the infant Chestburster stage develops – instead of simply being implanted as a fetus and growing within the host, the Chestburster is actually more akin to a cancerous growth that assembles itself using the host's own cells and biological material as building blocks.[1] The corresponding transfer of genetic material, referred to as the DNA reflex,[2] causes the physical attributes of the adult creature to vary.

The Xenomorph life cycle consists of five primary stages – the Ovomorph, the Facehugger, the Chestburster, the adult and finally the Queen. The adult stage can be further subdivided into a number of forms or castes, each with differing physical characteristics based on age, function or the genetic makeup of the host creature.

Early Life Cycle

Stage I: Ovomorph

Main article: Ovomorph (Egg)

The Ovomorph or Egg is considered to be the first stage of the Xenomorph's life cycle.[3] Eggs are laid by a Queen and are large, ellipsoidal leathery objects between two to three feet high with a four-lobed opening at the top. As a potential host approaches, the Egg's lobes unfurl like flower petals, and the parasitic Facehugger within extracts itself from within and attaches itself to the potential host.

Beyond artificially produced Ovomorphs, there are two ways an Egg can be produced, either birthed by a Queen, or through Eggmorphing.[4] Eggs produced by a Queen are naturally hardier and healthier than those created through Eggmorphing.[5]

Stage II: Facehugger

Main article: Facehugger

A Facehugger attached to Thomas Kane.

A Facehugger is the second stage in the creature's life cycle.[6] As its name suggests, it attaches to a victim's face, and its sole purpose is to impregnate them orally with the beginnings of a Xenomorph embryo. Upon making contact with a potential host, the Facehugger quickly renders them unconscious through the use of a cyanose-based paralytic chemical.[7] The Facehugger then inserts a proboscis down the host's throat, supplying it with suitable atmosphere[8] whilst simultaneously implanting the next stage of the creature's life cycle. Attempts to remove Facehuggers generally prove fatal,[9] as the parasitoid will respond by tightening its grip and suffocating the host, while the Facehugger's acidic blood prevents it from being safely cut away.[8] Once the Xenomorph embryo is safely in place, the Facehugger detaches, crawls away and dies.

Stage III: Chestburster

Main article: Chestburster

A Chestburster immediately after "birth".

Arguably the most biologically intriguing stage of the Xenomorph's life cycle, the Chestburster is not implanted into the host as an embryo but is in fact akin to a cancerous growth; it begins as a tumor that causes the host's body to literally construct the infant creature from its own biological material.[1] This process causes the developing embryo to take on some of the host's physical traits via a process known as the DNA Reflex,[2] including bipedalism, quadrupedalism[10] or even possessing the mandibles of a Predator[11] and other body structure changes. Over the course of 1–24 hours, and sometimes up to several days in the case of some Queens, the tumor develops into a Chestburster, at which point the creature emerges, violently ripping open the chest of the host, killing it. Owing to its cancerous nature, Chestburster development is typically fatal for the host even if the growing organism itself is surgically removed.[12]

Samuel Brett holding the Alien's molted skin.

Immediately after the Chestburster erupts from the body of its host, it will typically flee and find a secure location in which to molt into its adult form – at this stage in its life, the Xenomorph is in fact quite vulnerable. Initially, the Chestburster is less than 1 foot (30 cm) tall. However, it soon undergoes a dramatic growth spurt, reaching adult size in a matter of hours; aboard the Nostromo, the infant Alien grew to be over 7 feet (2.2m) in height by the time the crew located it again.[8]

Stage IV: Drone

Main article: Drone

A Drone.

The Drone is the most basic and common form of Xenomorph found in the Hive. They serve as both the species' primary assault caste and the gatherers of new hosts for impregnation. They are fast, strong, reasonably tough, and savage combatants. Even in death, the Drone is dangerous, as its highly pressurized bloodstream will cause it to burst apart when killed and drench nearby enemies in acid. Drones have been known to have both smooth and ridged heads, as well as other minor physical differences such as the presence of prominent blades on the upper forearms.

Runners and adult Praetomorphs, known as 'Stalkers' also fall under the Stage IV category.

Stage V: Warrior, Worker, Sentry

Essentially a subcategory, adult Drones will evolve into Warriors (or 'Soldiers'[13]), that will protect hives from invaders. The Runner equivalent of a Warrior is a Sentry.

Workers (also known as 'Weavers'[14] sees the Drone, shrink by 1.2-1.8 meters, become a sickly grayish-white color and grow a long pink proboscis that secretes Hive resin. They are largely responsible for the construction and maintencance of hives, but will leave their protection to Warriors and Sentries.

Stage VI: Praetorian, Crusher, Queen

Main article: Praetorian
Main article: Crusher

A Praetorian.

Praetorians are considerably larger than most other adult Xenomorphs, typically around twice the size of a Drone, but are smaller than Queens. When a hive reaches large population numbers, Workers will feed a Queen's chosen Warriors Royal Jelly until evolution into a Praetorian takes place. They act as guards to the Queen within the Hive (their name taken from the Praetorian Guard, the loyal bodyguards who would protect the Emperor in Ancient Rome). They are easily distinguished by the large, flat crest, like a crown, that extends from the rear of their heads. It is thought Praetorians may be capable of molting into a Queen if no Queen is present. Praetorians possess much more concentrated acidic blood, and they have been seen to produce a deafening scream that will summon additional Drones to their aid.[15]

The Runner equivalent of a Praetorian is a Crusher (also known as a 'Charger'[16]). After being force-fed Royal Jelly and raw metals by Workers for several weeks, a Runner will cocoon itself in resin and transform. It now becomes far bulkier, and grows a massive head crest. Crushers are quite rare, and only appear in hives that have been active for an extended period of time.[17]


Main article: Queen (caste)

Ellen Ripley encountering a Queen on Acheron (LV-426).

Xenomorph Queens are generally considered the apex of the species. They are significantly larger and stronger than basic Drones and even Praetorians. They are approximately 20 feet tall when standing erect and 53 feet in length.[18] Their body structure differs also, having two pairs of arms, with a smaller secondary pair of limbs located on the chest. The Queen's head is larger than other adult Xenomorphs and is protected by a crest, similar to that on Praetorians but considerably larger. The exact shape of the crest can vary from Queen-to-Queen. Unlike other Xenomorphs, the Queen also has high heel protrusions from its feet.

Egg-laying Queens possess an immense ovipositor attached to their lower torso, similar to the enlarged abdomen of a queen termite. Unlike insect queens, there appears to be no need for drones to fertilize the Xenomorph Queen.[11][19] When attached to its ovipositor, the Queen is essentially immobile and her body is supported by a biomechanical "throne" that consists of a lattice of struts resembling massive insect legs.[15][20]

Stage VI and above

Though reports of a Queen evolving beyond her current caste is incredibly scattered, it has been speculated that they can transform even further into an Empress or even a Queen Mother. Speculation of creatures known as Palatines and King Aliens are also present.[21]

Behind the Scenes

Eggmorphing: The original life cycle

Main article: Eggmorphing

In the initial cut of Alien, the Alien possessed a complete reproductive life cycle that did not require a Queen to lay more Eggs. Rather, the creature would cocoon its victims, dead or alive, in its Hive and subsequently convert them by unknown means into a new Egg containing a Facehugger, a process dubbed "Eggmorphing".[22]

This process allowed even a solitary Drone to continue the creature's existence. However, the scene showing this final stage was cut from Alien for reasons of pacing, leaving the ultimate origin of the Eggs in the film obscure. This in turn allowed Aliens director James Cameron to introduce a concept he had initially conceived for a spec script called Mother,[23] whereby a massive mother Xenomorph laid the Eggs and formed the basis for the creature's life cycle. Cameron conceived the Queen as a monstrous analogue to Ripley's own maternal role in the film.[23] In that vein, some critics have compared the Queen to Grendel's mother.[24][25]

Despite its deletion from the theatrical cut of Alien, the original life cycle was included in the novelization of the film,[26] while the movie footage was subsequently reintegrated in the Director's Cut from 2003.

The two methods of reproduction have never been reconciled in the films. However, the novelization of Alien3 suggests that both methods are typical of the species, and that the Eggmorphing seen in the Director's Cut of Alien is simply an alternate means for a Xenomorph to reproduce when a Queen is not present, or possibly even the means by which a Royal Facehugger is created.[27]

A Note on Egg Laying

In the Novel "Alien : Prototype," a Drone is able to produce one egg on its own without eggmorphing or the help of a queen. The implications in the novel are that an individual drone is capable of producing one egg at a time, but upon "laying" the ovomorph, it must have time in order to finish growth and development before it is viable as an egg with a facehugger. The novel would seem to indicate the maturation process of an egg laid in this way is either days or weeks, as heavy emphasis is placed on how secluded the drone made the egg so that it would have enough time to finish maturation before being found.

Conjecture; If both options of egg laying are canonical and viable, These separate methods exist likely so that even if reduced to a population of one, a hive could possibly repopulate, and the main difference between a drone and queens egg-laying is in Speed and Quantity, as a queen can produce many fully formed eggs in a short time, while a drone seems to take a prolonged time to produce even one egg which then must take even longer to finish maturation.


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