Xenomorph Chestburster

Species

• Xenomorph XX121

Skin Color

• Beige

Distinctions

• Rapid growth rate
• Appearance varies depending on host

The Chestburster, designated a "Stage 2" Xenomorph by Yutani scientists, is the infant form of the species Xenomorph XX121 and the third stage in its life cycle. It is most well known for its horrific method of gestation – it is implanted into a host lifeform's chest cavity by a Xenomorph Facehugger, and upon maturing it will erupt violently from the host's chest, killing them in an incredibly bloody and traumatic fashion. Chestbursters are small, generally not more than a foot tall and around two feet long including their tails, although larger examples have been seen.
Characteristics
Chestbursters resemble large worms, beige or brown in color and with a mouth of metallic teeth and a tail capable of propelling the creature at considerable speed. Some Chestbursters have been seen to possess arms, but this is not always the case, with others merely having small stubs where presumably the arms will eventually develop. It is possible a longer gestation period may determine the presence of arms at birth; notably, Queen Chestbursters (which have a considerably longer gestation period) have been known to birth with all four of their arms present, as well as legs and a partially developed head crest. Even regular Chestbursters have been known to birth fully formed, with arms and legs, essentially just a smaller version of the adult that it subsequently develops into. The reason for this is unclear, although it has been theorized that, in cases where a Chestburster is unable to escape its host's body at the usual time (perhaps due to greater structural integrity of the host's ribcage and chest cavity), the host may die prematurely as a result of the invasive organism within them, which will subsequently develop further until it is large and strong enough to emerge.
During development, the Chestburster is within an amniotic sac that is attached to the host via a small umbilical cord, through which it presumably gathers the nutrients it needs to grow. Owing to the Xenomorph's tendency to assimilate a degree of its host's genetic traits in a process dubbed the "DNA reflex", Chestbursters will also vary widely depending on the lifeform in which they gestate. For example, Xenomorphs born from Yautja will feature the mandibles of their host at birth.
Implantation
A Chestburster is generally introduced into its host by a Xenomorph Facehugger, although at least one Predalien – a juvenile Queen – has been known to insert infant Xenomorphs directly into a host without the need for a Xenomorph Facehugger. While the terms "impregnation" and "implantation" are liberally used to describe this process, they are not strictly accurate, no actual embryo is inserted into the host. Instead, the infant Xenomorph begins its life as a highly mutagenic fluid known as Plagiarus praepotens, which is injected into the host organism's chest cavity by a Xenomorph Facehugger. This fluid brings about chemogenetic restructuring of the host's cells, essentially "building" the Chestburster from the host's own biological material at a cellular level.
This complex process involves the absorption of organic material from the host, which is then broken down at a molecular level and rearranged into new compounds. Carbon units are disassociated and recombined into crystal lattices, which are used in the formation of the Xenomorph's hard body structures. Freed H+ ions are combined with surplus sulphate (SO42-) and nitrate (NO3-) groups to form the basis of the creature's highly acidic blood. As a side-effect of this unique process of development, Xenomorph genetic material is passed to the host as well as vice versa.
The manner in which the Chestburster develops from the host's genetic material means that the host's characteristics will in turn dictate, to an extent, the Xenomorph's physical features – embryos are thought to copy 10-15% of the host's genetic code via the DNA reflex. This genetic absorption is designed to help Xenomorphs adapt to the environment in which they are born, and also helps the developing creature to "hide" from the host organism's immune system. The assimilation of host DNA leads to physical variations in the adult creature. The Predalien Chestburster, for example, sports the signature mandibles of the Yautja (and grows dreadlocks upon reaching maturity), while quadrupedal hosts produce quadrupedal Xenomorphs. It is also theorized that the intelligence and instincts of the adult creature may be influenced by the host.
Gestation
Gestation of the Chestburster is rapid; the creature's signature inner jaw is known to form within an hour of implantation. However, the gestation period seems to be inconsistent, with most documented cases ranging from a few hours to almost a full day. In the case of Queen Chestbursters, gestation is substantially longer, taking as much as several days – thought to be a result of the significantly more complex physiology of the creature.
During the formation and growth process, the host initially exhibits no considerable outward negative symptoms, although symptoms build acutely after detachment of the Xenomorph Facehugger, the most common being a sore throat, slight nausea, increased congestion and moderate to extreme hunger. During the extended gestation period of an embryonic Queen, symptoms may additionally include a shortness of breath, exhaustion and internal hemorrhaging (detectable through biological scanners and present in nosebleeds or other seemingly random bleeding incidents), as well as chest pains inflicted either by the lack of chest space due to the Chestburster's presence, or even premature attempts to escape the host.
However, these negative effects are seemingly not ubiquitous – some hosts have reported actually feeling healthier than normal during the incubation period, a fact attributed to heightened levels of endorphins and adrenaline in their blood stream. It has been theorized that this increase in endorphins may be a subtle form of self-defense on the part of the Chestburster – the resultant feeling of well-being renders the host less likely to seek treatment following their attack. A similar adrenaline spike can also seemingly occur during birth, perhaps explaining why Larry Purvis was able to absorb several gunshot wounds at close range and still overpowered another healthy man before the Chestburster within him emerged from his chest.
Owing to its unique method of creation, the development of a Chestburster is inherently tied to the health of its host. While Chestbursters have been known to emerge successfully from recently deceased hosts, the death of the host early in the development process will also prove fatal for the embryo. Certain physical defects are also known to adversely affect Chestburster development.
Emergence


When fully developed, the Chestburster releases enzymes that soften the bone and surrounding tissues of the host's chest cavity to facilitate its egress, before finally forcing its way through the sternum. While the host may experience some discomfort in the minutes and hours leading up to the event, including mild chest pain and nausea, the actual emergence itself is rapid, with the Chestburster exiting within seconds of the onset of severe pain upon the host. The process begins with cramp-like pains in the victim's chest but rapidly progresses to debilitating agony and uncontrollable convulsions. When the Chestburster finally emerges it induces severe trauma, organ rupture and massive blood loss; death is almost instantaneous, but excruciatingly painful.
The Chestburster is arguably the most vulnerable stage of the Xenomorph's life cycle. While it grows rapidly, the infant is initially almost defenseless, save for its acidic blood. Unlike later adult stages, which have a hard exoskeleton capable even of repelling small arms fire, Chestbursters have a skin of soft, penetrable tissue. If born in a populated area a Chestburster will immediately seek escape, preferably via a means that will not allow easy pursuit (e.g. through air ducts or vents, possibly going as far as burning a hole in a wall or floor with its own blood). While they have been known to attack and kill humans even in this infant stage, the Chestburster's proficiency in this regard is limited and the creatures are known to simply prefer hiding until they reach maturity. If undisturbed, newly born Chestbursters may possibly consume parts of the human victim for sustenance.
The extreme psychological impact of the Chestburster's birth mechanism has actually been known to have an adverse effect on the survival of other embryos – witnesses to the gory spectacle who discover they are impregnated themselves often seek to end their life before enduring such an agonizing end, whether through their own actions or euthanasia. This can be fatal for the Chestburster, although depending on the manner of death it is possible for it to survive even after the host has died and emerge later. Stasis is known to halt Chestburster development and prevent birth.
Few materials seem to be immune to a Chestburster emergence; Chestbursters have been known to burst through Colonial Marine body armor. It is unknown whether the Chestburster employs measures such as its acidic blood for this purpose, or whether it is simply its sheer strength that allows it to punch through tough material.
Growth
After emergence, Chestbursters grow incredibly rapidly. They will immediately seek a place to hide, subsequently consuming organic materials and raw metals to increase their mass.
Survivability
While the birthing of a Chestburster is inherently fatal, it has been claimed or proposed on several occasions that removing a Chestburster before it emerges is possible, leaving no long-term residual effects to the host.
There exists at least one documented case in which a Chestburster has been removed successfully and the host has survived. However, it has been postulated that survival was solely as a result of altered genetic structure.
However, research has shown this to be inherently futile – the cancerous development process that creates the Chestburster means that, even if the embryo were safely removed from the host, they would soon develop a number of terminal tumors that would cause them to perish in a fairly short period of time.