On the topic of food, the Anchorpoint Essays make several viable theories:
QuoteIn order to reach its full size (that of approximately 2 meters), in a time span that has been recorded to range from two to three hours, it would need an extremely high metabolism. In order to fulfill the body's needs brought on by such a high metabolism there would have to be vast amounts of ingestion. Dr. Mason Wren speculated that the young Alien has a metabolism approximately 32 times greater than that of its adult counter parts. We do know that it molts very much like an insect (though the sheddings more closely resemble those of a reptile). The supplied data acquired by Wren and his team seems to indicate that the Alien molts only one to two times before reaching adult size.
It has been hypothesized that the Alien aboard the Nostromo managed to infiltrate the ship's food stores - however, this has never been verified. With the amount of food available and the creature's apparent metabolic rate this may account for the Alien's growth. Yet the vast majority of the chestbursters that were born on LV-426 did not have the installation's food stores at their disposal. So then what did the hatchlings ingest? Working with I. raptus' biology (a biology based on, carbon, fluorine, and silicon), and its nature as a biomechanical organism, it is thought that the creature may be able to rely on inorganic material as a means of assail the needs of the an extremely high metabolism: specifically carbon-rich compounds and minerals deposits. Because carbon is the most astronomically common element in the galaxy (over 10 million carbon compounds are known to exist, with thousands being vital to organic life and life sustenance) I. raptus would have a wide array of ingestible possibilities, regardless of the environment. The means of ingestion would most likely be through a method expectoration and ingestion: the I. raptus hatchling would expectorate onto the desired substance letting its acidic properties break down it down, and then ingest the now carbon-rich liquid. Given the natural environment of LV-426 and the proliferation of steel, plasti-steel, and various steel alloys within the structure that housed the hive it is likely that there was an abundance of material to sustain the large number of hatchlings. This is also applicable to the Alien found on Fiorina 161: the air in-take vent that the young Alien chose to molt in was rich in carbonate mineral deposits that were pulled in through the massive in take fans. The scrubbers for these in-take systems were often overwhelmed by the air-borne contaminants pulled in from the outside, and as a result the ductwork had to be scraped and cleaned on a regular basis. A similar approach can be applied to the Nostromo as well: Engineers Mate Brett was reported to have found the an I. raptus molting in the Mining and Excavation Storage Facility - an area that would be rich in carbonate mineral deposits left on various machines and steel machine parts. Though no corrosive damage was visually accounted for, it is likely that the hatchling used some of this residual mining debris and some of the materials used in the construction of the machinery as a means of supplementing its nutritional needs. This, coupled with the location of the creature's molt seems to be a more likely means of feeding than the ships food stores. (The development of the exoskeleton during this stage is discussed further in the Exoskeleton essay)
There exists a second theory as to how the hatchlings on LV-426 received nutritional sustenance: trophallaxis. This idea would remain consistent with what we know of various social insects and organisms. The transference of food via regurgitation between adult and young is a common practice as well as a means of creating and identifying chemical bond between the young and adults of a given nest among a specific species. It is widely believed that in a hive setting I. raptus hatchlings will rely largely upon the presence of the adult members of the brood for nutritional sustenance. The exact chemical composition of this regurgitated material is not known, but it is believed to be extremely high in proteins and carbon. Given the growth rate of a typical Chestburster it is believed that a single hatchling may engage in trophallaxis only once, or possibly twice before development is complete and molting occurs. It is further believed that the saturation of necessary dietary aids in the regurgitant is incredibly high allowing for a quicker developmental rate of hatchlings than those left to find food sources on their own.
It is a commonly accepted view that trophallaxis is the primary means of sustenance for I. raptus young when born in a hive structure. The ingestion of inorganic material is presumed to be a secondary means of nutritional intake and is rarely engaged in while in a nest. It is most likely a behavior that is related only to when an Alien is isolated from a hive, and is otherwise alone as a species.
This is where I usually go when I need a question answered about alien biology (and anything else for that matter), because the amount of research and effort put into these essays is astounding. I also use SM's Alien Encyclopedia, which is a very handy and extremely well researched guide.
