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No natural alien strains have eyes but, in fact, use a very sophisticated pheromone detection system to track prey. Xenomorphs seem to be very good with spatial awareness which leads to the theory that they also perhaps use some kind of sonar or echolocation to move about.
The range of vision appears to be very large in Xenomorphs, being greater than 180 degrees, and even potentially up to a full 360 degree area.
Most lower caste strains of Xenomorph (Facehugger, Chestburster, Drone, Runner, Predalien, Flyer) appear to have the intelligence level the same as many mammalian carnivores such as dogs or wolves, having some problem solving skills and learning ability in cause and consequence. In limited instances, Drones have set traps for prey. Higher castes such as Praetorians and Queens have a higher intelligence though the exact level is not known. Queens have been shown to understand and extrapolate human intentions, sending away attacking Drones in order to save Eggs. They have also been seen to have some superior problem solving skills. Über Queens are thought to have an intelligence level at least the same as humans, able to communicate telepathically with speech, and able to coerce certain individuals to accomplish plans.
First and foremost in Xenomorphic Internal Properties, is their acidic blood. Found to be a molecular acid, the blood is able to melt or burn through most known materials with only a very few exceptions. On the other hand, this acid blood quickly neutralizes on contract with oxygen, remaining acidic only for a minute or two at the most. The blood quickly loses its acidity after the death of the alien as well. All alien strains are shown to have this acidic blood.
Xenomorphs of course have an exoskeleton. This exoskeleton is incredibly durable, resistant to acid, and even most non-armour piercing ammunition due to the fact that Xenomorphs are silicon-based lifeforms (as opposed to most known life, which is carbon-based). Though they have an exoskeleton, it appears that some if not all adult strains of Xenomorph do in fact, have an endoskeleton (or internal skeleton) as well, as Predators frequently take Xenomorph skulls as trophies. This combination of skeleton types makes the Xenomorphs incredibly resilient and able to fall from massive heights with little or no damage. Xenomorphs are also resistant to extreme heat and cold.
Xenomorphs most likely have some kind of internal muscular tissue, as Xenomorph meat is a favourite food of Yautja Predators.
Little is known about the Xenomorph's digestive system or its need for nutrients. Some developing Xenomorphs have been known to feed on small animals, perhaps a way to increase the speed of growth to full adulthood, but it has been shown that food during this time is not necessary to survival. In a hive situation, nothing is known about feeding.
It also seems that the Xenomorph's blood is not pumped through a series of arteries and veins but runs between two layers of tissue and is highly pressurized, resulting in a large spray of the acidic blood if the alien is injured. Xenomorphs also appear to have an incredibly fast clotting system, as even the flow of blood from the removal of a limb stops within moments of the injury occurring, leaving the individual barely weakened by such a massive wound.
Worker Drones have been shown to be able to exude a sticky substance used for creating hives and nests. This resin quickly solidifies into a very hard but brittle material. It is possible the resin substance is a variation of the substance some castes use to wall-walk.
Communication appears to mainly take place using some kind of telepathy, Queens are able to command drones, often in defense of a hive, from a great distance and Über Queens are apparently able to coerce and command humans from light-years away.
As Xenomorphs also use pheromones in hunting, it is likely they can also use pheromones to communicate among each other in certain ways. Body language is also a likely means of communication in a limited sense.
It is also thought that Xenomorphs pass on a certain collective history and knowledge through a hive's genetics, which will allow any individual to be at its full capacity as soon as it reaches full adulthood.
The question of "Do Xenomorphs Breathe", at least in a conventional sense, has been a long debated one. It has been shown, in a cold environment, Xenomorph's breath can in fact be seen, but it appears, if that is actually breath and not some other Xenomorphic ability, they do not breathe as often, and therefore more efficiently than humans and most other animals. Xenomorphs have been known to be able to survive for an undetermined amount of time in an oxygen-less and gas-less environment. Whether they breathe oxygen is another unknown as they are silicon-based.
One of the most interesting of all the Xenomorphic abilities is the lesser castes's (Facehugger, Drone, Runner) ability to wall-walk, to cling to any surface and move around at incredibly speed, even upside-down. It is doubtful that such large creatures could use miniscule hairs as most Terran insects do, but more likely, exude some kind of sticky material on their limbs to help them stick to walls and ceilings.
Some Xenomorphs have proven to be excellent swimmers, though most likely, only the Drone Caste excels at this. Most other castes are not streamlined enough. Certain hives appear to have slight variations of the drone strain with a longer tail topped with what could almost be called a fin, and with webbed hands and feet. The tail seems to be the primary form of underwater propulsion, in a very similar way to Terran crocodiles and alligators. These Xenomorphs can reach very high speeds underwater.