The first stage of the alien's lifecycle consists of an egg. The eggs are complex organisms in and of themselves. They are responsible for maintaining life support for the larva for an indefinite amount of time, and must recognize a potential host and distinguish it from valid members of the nest.  Eggs are initially created inside a queen alien and enter the world (after being queued in her extended abdomen) via slimy tube to stand on their own (indicating that there is a definite "up" side and "down" side to the egg). The egg itself is a leathery object approximately 2.5 feet tall.

 The egg can survive for an undetermined length of time in various environments.  The egg appears translucent, is flammable, and unarmored. The egg detects when a host is proximal by sound and/or movement. As this happens, some sort of liquid seems to drip upward(!?), and small bumps appear as  the egg comes to live, awakened by the chance to continue it's lifecycle. The petals(?) at the top of the egg open, preparing for the next stage as the face-hugger.

The next stage, hibernating inside one of these eggs, is a parasite commonly refereed to as a face-hugger. Concealed by the egg for protection, the facehugger waits until the egg senses it is time to continue the life cycle.  When a viable host is brought near a closed egg (either by curiosity, or being cocooned and held in place) it triggers the "contents" of the egg to come to life. The egg opens from the top to reveal the creature within it. At this point the cycle transfers from the egg to the next phase as the face-hugger awakens.

Developing inside the host, this stage of the lifecycle is refereed to as the embryo or spore stage. This begin before the facehugger has actually departed from the host. Immediately after the embryo has reached the body cavity suitable for gestation (from the transplanting of the facehugger's long tube), it begins to feed off of the host. Using the host's fluid and resources, the embryo grows and develops. This can take a period of anywhere from a few hours or a few days

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Stage 4: Chestburster

When the embryo has completed it's period of development inside of the host, it emerges into the next stage in it's life. The burster has built up enough strength into order to tear out of the body cavity inside of the host. The host experiences a great deal of pain during this procedure, resulting in convulsions and loss of all rational thought. This process usually results in the death of the host, which in all practical means isn't all the greatest of way to ensure the reproduction of the species. It would be more efficient if the host were reusable for many aliens, but due to the aliens violent nature, it is only fitting for it to cause death upon birth.

This is the final stage in the development of the standard xenomorph -- although there is great speculation of further development. In the previous stage, the creature was roughly one to two feet tall. In an extensive growth increase, it manages to become approximately 7 to 8 feet tall in a matter of hours. During this growth stage it is sometimes referred to as a 'calf', and sheds at least one layer of skin -- similar to a snake.  In the usual case this increase in mass would take much longer. We can also assume that is sheds skin multiple times in its rapid growth.  Whether the alien needs any food at all for growth is has not been fully determined.  The xenomorph's skin appears a chitin like shell similar to bugs. It is hard, dark (black/green), and acts as an outer shell (exo-skeleton). It is by no means impervious (easily shattered by bullets), but has a higher tolerance to fire.  It contains acid for blood, which tends to spray when hit by bullets.

 During it's growth its cranium becomes elongated, and at full development the xenomorph has a banana-shaped skull.  Although they have this large cranium, xenomorphs have rudimentary thinking skills.  The large skull may also serve the purpose of pressurization, hold some vital fluid, or to maintain balance.

Another attribute seen in the adult is the long dark spines sticking out of the back. These could be functionally similar to the plates on the back of a Stegosaurus; they make it difficult to land a damaging blow on the alien from a sneak-attack from behind. The spines could also be some form of reservoir for acid (similar to the humps on a camel). Perhaps they could be heat sinks or some sort.

They have a "double jaw", or 2 mouths -- one inside of the other.  The outer jaw is hinged primarily by tendon-like apertures and is supported similar to that of a snake. The second jaw (also referred to as the "tongue") can extend out to about a foot long reach. It has a very strong driving force (enough to easily puncture skulls), almost like a pneumatic power. (possible another use of the elongated cranium).
 

 The xenomorph's tail has grown proportionally and is not only used for balance, but attack. It has a barbed "stinger" at the end of it and uses it as an attack. The tail itself has a long row of connected spines along the top of it (similar to what a dragon would have).

 The adult is also extremely agile. It can leap from wall to wall and crawl on the ceiling.  The creature also has amazing mechanical-like strength.  They manage to pound through metal doors and walls, becoming virtually unstoppable.

 The speculation of further development lies upon alien interaction of a society. When there is no queen present (or eggs) many different things could happen. A present xenomorph could morph into a queen through a cocoon like transformation. Or, a standard alien could have the capability of laying one egg in order to produce a queen.

The Queen Alien- little is known about her.  Some things that we do know about the queen: she has a much larger cranium than the usual alien and is slightly taller (approx. 2-3 feet). The queen has the ability to create and lay eggs (through the use of the extended abdomen) and she has the ability to survive without the extended abdomen (for an unknown amount of time).

 The queen is the prime focal point of the colony and the driving control force. All the aliens (worker and drone) strive to support her.  She noticeably has more arms/legs that the usual aliens -- 2 legs, 2 large arms, 2 smaller arms, and 2 very short arms sticking straight out of her chest for a total of 8. When we first see a queen, she is huge. Upon later observation, a large portion of the initial queen is basically her nest (designed to support her and her rather large abdomen (eggsac). She is still undoubtedly larger and it seems that even her outer jaw can retract further (you can notice this in the first up close shot of the queen).

 Fighting tactics for the queen include use of her tail and plain brute strength.