The adult alien is one of the most versatile and deadly creatures documented. It posesses strength and agility far greater then that of humans or any indiginous creature of earth. Its appearance is frightening in itself but what is more frightening are there unmatched hunting and defense skills. It posesses an incredible amount of strength. The adult has a protruding jaw capable of shattering skulls with its snapping strength. The adult alien has several very effective defense mechanisms. The adult, like the facehugger, chestburster, and queen, also has highly concentrated acid for blood. If an alien is damaged severely or killed at close range by another organism, that organism will most likely suffer at least severe injury as a result of the acidic splatter.
The adult is roughly two meters tall with a strong tail that extends to the height of the body, and it is generally bipedal. Speculation suggests that the Xenomorph is a polythermic creature due to the problems surrounding it being a endothermic or ectothermic creature mainly because it produces no body heat. This means it's the first of its kind. The long head of the adult may be due to housing an enlarged brain which doesn't necessarily mean a greater intelligence, but a more complex one. It has been speculated that a translucent cowl on an Xenomorph's head shows it's at a young age. As it gets older it loses the cowl, exposing distinct textured lining. The reason for the cowl is probably to serve as a protective shell for the still developing cranium.
The adult Xenomorph also generally has five spine-like appendages extending from its back, and the uppermost can be seen to be no more than an exaggerated vertebrae which could aid in warding off rear attacks or just to make the Xenomorph seem larger. The other four tube-like appendages have been hypothesized to contain glands that secret a type of resin much like that used to construct a hive which would aid the Xenomorph in dropping down onto prey or ascending great heights while leaving the arms, legs, and tail free for use. It is also possible they are used to secret the resin that the hive is constructed of, but it would be easier just to regurgitate that substance. At this time, it is unknown how the Xenomorph's create the resin within their hive.
Several encounters with other classes of the adult Xenomorph do not have dorsal spines. It is theorized that these adults evolved from four-legged host and as a result the spines would interfere with the Xenomorph's head when held upright on all fours. So the Xenomorphs have adapted during the embryo stage by altering the DNA to shrink the spinal glands. The secondary jaws of the adult, which are part of a modified tongue, are used in an offensive manner and can spring twelve inches outward from the Xenomorph's mouth. The second set of jaws primary purpose is immobilizing a potential host but they can also be used to frighten hosts into a shocked catatonic state. The jaws's tensile strength is greater than bone, and once it reaches its maximum length its jaws close and its "tongue" is retracted. The adult Xenomorph is also able to spit a concentrated ray of venom toward a potential host that can dissolve flesh and enter their blood stream, eventually rendering the potential host immobile. The Xenomorph's tail is very powerful and is used for agility and balance, an offensive and defensive weapon, and immobilizing potential hosts with its stinger. In aquatic situations, the tail also allows the adult Xenomorph to move with spectacular grace and agility.
It is assumed that the adult Xenomorph's detection organs are all located in or around its head, and are extremely acute. It does not appears the Xenomorph feeds upon humans, and what its dietary needs are have yet to be determined. Also, any internal organs an adult Xenomorph contains is still a mystery as well as its average life span.
There are two classes of the adult Xenomorphs. One is the drone the other is the warrior. The drone tends to the queen and is responsible for building and maintaing the hive. The warrior must retrieve hosts for impregnation and hunt for food. The warriors are far more deadly and fierce then the drone; but the drone is still far harmless, and still poses a great threat to any individually.