Xenomorph Life Cycle

The life cycle of the species Xenomorph 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.

Overview
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. The corresponding transfer of genetic material, referred to as the DNA Reflex, 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, and the adult. 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.

Ovomorph
"Full Article: Ovomorph" The Ovomorph, unofficially called an egg, is typically considered to be the first stage of the Xenomorph's life cycle. 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 and attaches itself to the potential host.

Facehugger
"Full Article: Facehugger" A Facehugger is the second stage in the creature's life cycle. 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. The Facehugger then inserts a proboscis down the host's throat, supplying it with suitable atmosphere whilst simultaneously implanting the next stage of the creature's life cycle. Attempts to remove Facehuggers generally prove fatal, 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. Once the Xenomorph embryo is safely in place, the Facehugger detaches, crawls away and dies.

Chestburster
"Full Article: Chestburster" Arguably the most biologically intriguing stage of the Xenomorph's life cycle, the Chestburster is implanted into the host as an embryo but also 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. This process causes the developing embryo to take on some of the host's physical traits via a process known as the DNA Reflex, including bipedalism, quadrupedalism or even possessing the mandibles of a Sangheili and other body structure changes. Over the course of 24 to 72 hours, and sometimes up to several days, 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.

Growth and maturity
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.

Drone
"Full Article: Drone (Xenomorph caste)" The Drone is the most basic and common form of Xenomorph found in the Hive; the Drone form acts much like worker bees or ants. The Drones' main function is to keep the Hive functioning properly and to gather new hosts for impregnation. They are almost identical to Warriors in appearance with the exception of their smooth, domed skull, and their tails, which end in a stinger-like barb as opposed to a large blade.

Warrior
"Full Article: Warrior (Xenomorph caste)"The Warrior (also called the Soldier or Hunter) is the primary assault caste of the Xenomorphs. They are fast, strong, reasonably tough, and savage combatants. Even in death the Warrior is dangerous, as its highly pressurised bloodstream will cause it to burst apart when killed and drench nearby enemies in acid. Warriors have ridged heads, as opposed to the smooth carapace of the Drone, but are otherwise virtually identical; because of this, Warriors are often said to simply be the mature life stage of the Drone.

Praetorian
"Full Article: Praetorian (Xenomorph caste)" Praetorians are considerably larger than most other adult Xenomorphs, typically around twice the size of a Warrior, but are smaller than Queens. 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 Warriors to their aid.

Queen
"Full Article: Queen (Xenomorph caste)"Xenomorph Queens are considered the apex of the species. They are significantly larger and stronger than basic Warriors and even Praetorians. They are approximately 20 feet tall when standing erect and 53 feet in length. 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 Egg sac 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. When attached to its Egg sac, 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.

Empress
"Full Article: Empress (Xenomorph caste)"