In the movies Alien and Aliens, what do the aliens eat? You would think they first feed from the body host, but then when the human host awakens he doesn't have anything visibly wrong, so the human host was used only to incubate the young alien. When they get out of the body they keep growing but when they encounter humans, they don't eat them, they just kill them or use them as new hosts.
So, what do they eat? How can they grow that tall?
There is no canon info available (confirmed by searching most Wikis and many many forum discussion threads). The only 2 points of info are:
There is an possibility that the "inner mouth" is used to drink blood from victims
One forum post mentioned that "I believe in the RPG book published by Leading Edge Games, it was written that the aliens eat some pretty strange stuff, glass and dirt was on the list. I guess those two would make sense since the alien has a silicone cell structure?"
Mostly, it seems like the answer (discarding the games) is "it's not known what they eat, or whether they even need to eat at all".
In addition, the creature has an armored, acid-proof carapace, as well as pints of hydrochloric or hydrosulfuric acid for blood, copious amounts of mucus-like drippings, able to spin catacombs from fluids in its body, able to sprint at speeds of twenty miles per hour, and has the strength to rip through body armor. I find it hard to believe it can do this on a single meal of human heart, blood, liver, kidneys and assorted sweetbreads.
Since we have never seen them eating, we have to infer from what is in their surroundings, what they could consume to continue to put on mass, muscle, armor and blood to become the formidable killing machines we know them to be. We can use the first two movies for our extrapolation.
In Alien, there is a single creature and all it has to eat are the humans on board the Nostromo and anything they brought with them. It was shown that Ripley found an empty storage container during the hunt for the creature. So, it can be assumed, it needed mass to grow and in this case was able to eat the food of its host creature to survive. This seems reasonable if the creature has taken some of its biology from the host, ensuring at least some level of compatibility with the organisms ecosystem and food supply.
It can also be inferred there was more than one storage container of that type on the ship so it does not take much to assume human food, plus the humans it killed during the hunt were sufficient for it to get the mass it needed to grow and expand in size.
All of its advanced biochemical processes as well as its silicon makeup would probably be able to be met by the technical equipment that made up the ship in the form of metals and other inorganic materials found in a starship of the size and complexity of the Nostromo. Unless a thorough scan of the ship was done, it would have been able to eat its fill of inorganic material and it would never be noticed or missed by the crew.
In Aliens, we have almost the same conditions, a sizable human base, plenty of human food stores, a significant number of humans to eat (and drink from, blood is a decent source of iron and lesser minerals) and refined inorganic materials in great abundance. So their growth, size and numbers can be presumed based on the amount of food available. We can assume they may be biologically efficient, processing a greater amount of energy and converting more mass than we do, so it may not take much organic material for a Xenomorph to develop physically, which is why they are so willing to abandon their host if the nymph finds itself in danger.
In summary, Xenomorphs eat what their hosts eat and can likely find a source of inorganic material compatible with their biology on any planet they find themselves on (Silicon is the eight most abundant material in the universe and the second most abundant mineral compound on Earth). This high level of adaptability would surely make them an Alpha predator on any world they had sufficient compatible inorganic material for them to complete their molting and grow to their adult size.
The only reference in any of the films is in Alien. Ash and Ripley are discussing the Alien and Ash says, "Yes, well, it's adapted remarkably well to our atmosphere considering its nutritional requirements. The only thing we don't know about is temperature."
Ash also says, "Has a funny habit of shedding his cells and replacing them with polarized silicon, which gives him a prolonged resistance to adverse environmental conditions."
Those two quotes strongly imply that Aliens don't eat meat or drink water / blood. Firstly, eating the same foods we eat wouldn't make it remarkable for the Alien to adapt to our atmosphere.
Second, you can't produce silicon based cells from eating the same types of food we eat.
To continue, while we do see humans being killed by Aliens, they definitely don't use them for food. In the second film we see that all of the colonists are cocooned under the cooling towers. PDTs still transmit even if the person is deceased and if Aliens ate humans, it's likely that at least one Alien would have consumed a PDT and would have appeared on the colony map when Hudson was trying to locate the colonists.
Even if they do eat humans and somehow managed to avoid eating the colonist PDTs, that would have prevented them from producing over 100 aliens. Ripley comments that there would be "over 100 at least" if each colonist were impregnated. Throughout the film we see over 100 aliens.
The Alien species must survive by eating rocks, metals, or some other source of non-carbon based food.
Although the information provided by a number of wikis on the subject is likely non-canon (since it is likely based on comics, books, games, and perhaps just prevailing theories), I thought it may be worth noting here for anyone interested:
From the Chestburster entry of the Aliens wiki:
It's egg is laid in the host's bronchial tubes by a Facehugger, where it hatches. It then burrows for the host's aorta (major artery in the heart), where it feeds on absorbed nutrients and white blood cells. ... After about an hour or two, it lets go, and begins swimming about in the host's body, causing mild discomfort. Then, it finds the sternum, and starts chewing. This causes the victim great pain, shock, and blood loss. Then, true to it's namesake, it pops out, and finds a nursery or chicken coop, or, less messy, a food locker, something with a large amount of helpless meat.
From the Chestburster entry of the AVP wiki:
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 which has both the Alien proteins and the Host's.
When fully developed, the creature releases enzymes that soften the bone and surrounding tissues and starts chewing the sternum. This causes the victim great pain, shock, and blood loss. Then, true to its namesake, it pops out. If far away from the Hive it cannot depend on the adults so it actively searches for a nursery, chicken coop, or a food locker, something with a large amount of organic or inorganic matter (such as metals) which it softens with its acid fluids and directly converts into body mass. It also will attack and kill humans and feed on them, especially after emerging. They will eat anything off of the person: face, genitals, fingers, but primarily the organs (brain, heart, lungs, liver, kidneys). Then after a few hours to a few days, it turns into an adult Alien.
From the Xenomorph entry of the Aliens wiki:
The Xenomorph appears to moult before reaching maturity. Maturity is reached in a few hours, and involves a dozenfold increase in mass, which would presumably require some form of nourishment. In the novelization of the movie Alien, Ripley comes across a food locker that had been raided, apparently by the Xenomorph to get food. Whether or not this was nourishment to grow was not specified.
WARNING SPOILERS
Well after watching Prometheus (the so called semi-prequel of Alien) I came to the conclusion that the black goo that the Engineers engineered back there on moon LV-223 was the origin of the Alien. My theory, as far as I know, if Aliens are originated from the Trilobite/Facehugger (seen in Prometheus) and that this facehugger came to exist thanks to that black goo, then I may come to a conclusion that even though Aliens are living organisms, they are just a bio-weapon. As we saw on planet LV-426 the crashed bomber carrying Xenomorphs eggs (as the final stage of the proto-Xenomorph seen in Prometheus).
So my point here is that Alien is just a bio-weapon created to live for a certain term, kill whatever crossed its paths and die after a while. I guess the only purpose for them is the killing. They weren't meant to live for long. They were used as weapons.
But why do they get so tall, how is it that they grow so fast? Well this might answer your question:
In Prometheus the black goo changes living organisms very fast.
First of all, the worms that lived in that terraformed cave, where the bio-weapons/black goo were kept, after ingestion of that stuff they evolved in a matter of hours into a bigger mutated creature.
That same organic stuff was ingested by one of the crew members of the Prometheus and after sexual intercourse with his girlfriend caused the creation of the first born Trilobite or like we call it Facehugger. At first it was small, but hours after quarantine the Facehugger became a freaking giant squid! It was way bigger than the Engineers themselves.
So my point here is that this organism feeds on nothing. It was designed to evolve and react to its environment. Like I said before, its purpose is to kill everything and eventually host another living organism to reproduce themselves. So that's why they get so tall just in a matter of time. Because they were designed like that.
I hope my theory kinda answered your question :)
I always assumed that the large vents on their bodies drew in nutrients from the environment. The gases and ions present in the air providing for a portion of it's nutrition, while scavenging organic and inorganic matter providing the rest. The fact that the Xenomorph could survive on predominantly inorganic material is not implausible. Humans, like all animals, require minerals (metals), like zinc, copper, iron, magnesium, etc. in order to live.
These xenomorphs are obligate carnivores just like cats, which unlike dogs whom are not and which do, have no grinding surfaces on their molars, and apparently these aliens lack molar teeth entirely.
Much like the Tyrannosaurus Rex,
He [was obligatorily] carnivorous; a voracious meat eater. His teeth were designed for one function and one function only: to tear flesh from bones. – Dinosaur!
Judging by how the alien's teeth come together, they'd likely be classified as a sort of carnassial which are, "paired upper and lower teeth (either molars or premolars and molars) modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner."
"Additionally, this term [a hypercarnivore, is an animal which has a diet that is more than 70% meat], is also used in paleobiology to describe taxa of animals which have an increased slicing component of their dentition relative to the grinding component."
Seeing as how they have a parasitic requirement involving warm blooded animals to procreate their own species (and that we have good reason to assume that life similar to Earth's has or will evolve elsewhere), we have no reason to suspect that the (non) symbiotic relationship ends there. In fact, "About 10% of described insect species are parasitoids [...]" which are parasites that devour their host at some point during their life cycle.
I always thought of Aliens like sharks, who would eat almost anything that calls their attention. It's reasonable they wouldn't eat any possible hosts, though.
Eating glass, like one mentioned, would be a lame direction for the copyright owners to go... I mean, it's SciFi, so food must be organic. Only fantasy stuff would allow a character to feed from inorganic matter like glass, or, whatever, souls!
I guess the answers would be small creatures, fungus-like matter, dead hosts etc.
I have seen X-rays of the alien head showing no digestive system or entry from the mouth. My theory is the glowing organ that I saw under the dome head was something similar to photosynthesis that could turn energy from light to matter. This is how they grow and get energy like plants. However if this is true, it brings up the question of why would aliens kill non-xenomorphs?
I think the "Acid for Blood" may be in the answer . Like certain insects that use acids to break down their food, Aliens use their acid to break down metal, rock, humans so basically, they eat what ever they want.
In Alien 3, the prisoners happen upon the Xenomorph while it seems to be feeding on one of its victims. I always assumed from then on that the Xenos actually do eat, and they'll eat some of their victims and save others for cocooning. Then again, it may just have been doing it to make sure he was dead, and was just thinning out the prisoner population to minimize the risk to itself.
In AVP 2, the Predator-Xenomorph is seen dragging a deceased person and then piercing the victims skull 2-3 times in a row with its inner mouth before being interrupted by the Predator. You could argue that this is only because this particular xenomorph has Predator DNA...but then again no one has ever seen Predator eat so idk :/
In once of the AVP video games you could play as an Alien. During the Chestburster life-cycle you had to keep low and hide, surviving by eating small rodents found on the ship. This of course is not canon.
Regarding the comment about the aliens eating each other, there are 2 instances where they attack each other. Alien:Resurrection when 2 of them attack the a third in order to escape the cell they were in using the acid blood. The other was in AVP when the hunter/warrior type spilt the queen's blood on her chains, also in order to escape. One thing I note about this is they never spill their own blood on purpose. In Aliens 3 the alien seems to be killing all the humans. The last 2 movies are vastly under appreciated in my opinion. Other boards I'm been checking regarding whether they eat have mentioned the aliens having a shortened lifespan of a few days, like mayflies which don't eat during their lifecycle. Their sole purpose is to procreate, and provide food for other animals. Maybe they eat expired drones.
I think you guys are missing something obvious which is suggested admittedly in the comics. The chest burster runs away after it kills John hurt. Suppose no crew had been there (i.e. in a hive). Couldn't it have fed undisturbed on the corpse? A good reason for building gives. Also maybe the egg sack of the queen produces glucose or royal jelly (expanded universe I know).m
Everything I have seen (games, books and as others mentioned movies), has said that they eat meat. Example is in the book AVP: retribution, when a contained Facehugger victim burst open the Chestburster fed on its host.
I am not sure that they do need to eat at all, but kill for other reasons that I ignore. It is speculated that they obtain the energy not through digestion but from their acidic blood which acts sort of a battery.
References come from Aliens: Colonial Marines Technical Manual (in-universe) and Aliens magazine (1991).
