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Chestburster

Chestburster

Biographical information
Date and place of birth	Embryo implantation
Rank	Xenomorph infant
Physical description
Species	Xenomorph
Gender	Female
Height	1 ft.
Chronological and political information
Notable Facts	Can grow into an adult in just three hours. Appearance varies depending on host.

[Source]

The Chestburster is a Xenomorph infant (or Nymph because it resembles the adult and is not seen forming a cocoon to reach maturity). An egg is laid in the pharynx by a Facehugger (young PredQueens are known to insert embryos directly into a host without a Facehugger). It is speculated that it develops in a manner similar to that of the immature heartworm (Dirofilaria immitis) that migrates through the body absorbing nutrients before establishing itself. Far from the pharynx it's unknown if the embryo travels to the host 's stomach or to the bronchial tubes. Another theory says that the alien begins his life in the host body not as an embryo but as a tumor that later takes the shape of an immature alien. In this theory, what the Facehugger injects in the host is not an infant Xenomorph but a small egg that inserts its proteins in the host DNA and commands its cells to "create" the chestburster wich has both the Alien proteins and the Host's.

When fully developed, the creature releases enzymes that softens the bone and surrounding tissues and begins chewing through the sternum. This causes the victim great pain, shock, and blood loss. Then, as its name suggests, it emerges from the chest. If far away from the Hive, it cannot depend on the adults and so it actively searches for a nursery, chicken coop, or food locker. The newborn alien requires a location with a large amount of organic or inorganic matter (such as metals) which it softens with its acidic fluids and directly converts into body mass. It also will attack and kill humans and feed on them. They will consume any part of the human victim (such as facial extremities or genitals), but prefers internal organs such as the brain, liver, or heart. Then after a few hours to a few days, it reaches maturity as an adult Alien.

The host's characteristics determine the chestburster's features. The Predalien chestburster, for example, sports the signature Yautja mandibles (and grows the dreadlocks later), while quadrupedal hosts produce quadrupedal chestbursters (whereas chestbursters spawned from humans may not even have forelimbs). AVP Extinction suggests that genetic alteration might allow a Runner chestburster to split into identical twins after escape from a quadruped.

An embryo implanted in a pregnant woman will feed directly on the baby and/or placental fluids, and the chestburster will erupt from the stomach of the woman. They often raise themselves to a foot high and are 36 inches long.

Some chestbursters are born with arms as seen in "Aliens" but most are not.

They are very quick and in tune with their surroundings once emerged. If in a populated room they will immediatly seek an escape (i.e. through open doors, air ducts ore vents; possibly going as far as burning a hole in the wall or floor or ripping off or throught grate coverings).

"Aliens: Steel Egg" also shows that they do have regular body processes. One of the crew found a pile of scat with a human tooth inside of it while exploring the ventilation system.

The Predalien have the mandibles of their Predator hosts after they emerge and eventually grow the characteristic dreadlocks as well.