Chestburster

The Chestburster is the third stage in the life cycle of the Xenomorph species. This is the infant form of typical adult Xenomorph forms such as Drones and Queens. It appears as a gruesome, worm-like creature with a long, sinuous body and a mouth filled with sharp, metallic teeth.

Overview
The Chestburster begins life as an embryo implanted into a host by a Facehugger. It is little more than a collection of cancerous cells at this point, contained within an amniotic sac that forms inside a host's chest cavity during the impregnation process. The placenta absorbs genetic material from the surrounding host body, which can result in differing features of the Xenomorph depending on the species of the host. The mutagens injected by the Facehugger during impregnation bring about chemogenetic restructuring of the host's cells, essentially "building" the Chestburster from the host's own biological material at a cellular level.

Gestation of a Chestburster is rapid, normally taking only a few hours or up to a full day. Infant Queens tend to take longer to develop, a matter of days, due to their more complex biology. During the formation and growth process, the host initially exhibits no considerable outward negative symptoms, although symptoms build acutely after detachment of the 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 the impregnation.

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.

Once the Chestburster is fully developed, it will secrete an enzyme that softens the bone and muscle tissue of the host's chest region, allowing the creature to force its way out of the host body with greater expediency. The process of emergence is excrutiatingly painful for the host and always fatal. The host enters convulsions during the birthing, writhing in agony as the Chestburster pushes and gnaws its way through the host's sternum before erupting from the torso.

Upon birth, the Chestburster will seek out a dark, secluded space in which to continue growing. Since this stage of growth is when a Xenomorph is at its most vulnerable, it will avoid contact with any non-Xenomorph creatures until it has sufficiently grown and is ready to hunt. Though the Chestburster lacks a sturdy mesoskeleton, it is remarkably fast, whipping its tail to quickly scurry across the environment.

A Chestburster will feed on raw metals and whatever biomatter is available to sustain itself while it grows into its adult form. This growth process is short, taking only a matter of hours for the creature to reach maturity. The full growth process of a Chestburster into an adult Xenomorph has never been witnessed, so the process is yet to be fully understood.