The creature began as a single pile of organic matter that crashed into a quiet town in America and was approached by Grant. As he approached, the creatures first stage of its life began as it launched a type of organic harpoon at the human where it exchanged part of its DNA. The human would not feel much difference but a gradual shift would begin as the alien DNA would begin to exert more and more control over its host. It would develop a craving for red meat and begin to collect it; even from roaming animals.
It would then seek out the closest lone human who would be impregnated by the prime host, in this Grant, through two tubular tentacles with stingers on the end. These would emerge from the front part of the hosts stomach. Once impregnanted, the human would be isolated from the rest of its kind and chained in a secluded location. Once there, it would be held by restraints and develop a similar craving for red meat which the prime host would deliver. As this happened, the prime host would begin to mutate into a more alien form which appeared serpentine with no legs but travelling quickly via its long tail. Its arms would also become tentacles that could lash out and slice a human being apart which helped protect it from local predators, in this case - humans.
The impregnanted human would grow impossibly large yet still craving for food until it bursts apart. This is because of the development of smaller worm-like parasites which would be born in the thousands. These smaller parasitical worms would attempt to immediately find hosts to infest via the mouth. The worms would use their numbers to provide them a primary advantage until they reached striking range where they pounced into the mouth, forcing themselves into unwilling hosts. Once infested, the humans would be under the creatures complete mental domination and become a type of zombie which would attempt to kill resistance or subdue more hosts for those parasites that did not gain a host. These zombies would have no individual will and the memories of the prime host would be present in them where its thoughts would dominate the zombies speech.
While the territory was being converted for the use by the parasitical plague, the prime host would find a secluded location and begin bringing those hosts infected to its form where it literally absorbed their flesh into its form. This would continuously grow until the prime host was so large that it was incapable of movement. It would rely on its new 'zombie drones' to protect it and bring new hosts to it. These zombies would serve a few purposes; protection of the prime host, bringing more food, fusing new hosts into its flesh or to serve as living incubators as they were impregnanted by the twin stingers of the prime host.
The new hosts would differ from the first incubator who was not infested by the parasitical worms as these new incubator hosts would do so willing. They would also feast on red meat and grow so large until they burst once again with parasitical worms repeating the process and bolstering their numbers. This is the primary and only means the creatures reproduced. However, it was very important that the prime host be protected for its destruction would kill all the other parasites - and their hosts - due to a mental link between the organisms. If not stopped, all the host species would be absorbed into a single mass until it was the only form of life on the planets surface. After which it would attempt to launch a 'seed' into space and repeat the process on another world.
The creature was only concerned with its domination of the planet it was located at and the increase of its numbers. Despite this near animalistic quality, the creature was quite intelligent and capable of developing tactics. But whether this was a quality it developed from its hosts that it consumed or a natural aspect is unknown. It is interesting to note that the original behaviours of the host are adopted by the prime host and therefore adopted by the parasites themselves. Strong emotions like love to an individual can dominate the alien DNA and impart a sense of protection to those the parasites hosts loved. However, if faced with the possibility of destruction, then the creature will violently attempt to destroy any threats to its well being.
The creatures seem to use the tactic of numbers to overpower and overwhelm the host species without using advanced forms of weaponry but natural qualities. Infected hosts that develop into zombies also attempt to use their personal connections such as friendships as well as family relationships to trick the hosts into cooperating. Despite this, the creatures seem to have a fear towards flame based forms of attack, possibly because these are perhaps the only true form of attack that can possibly destroy the parasites. Even if the 'zombie' hosts are decapitated, the parasite inside can survive, leave the host and attempt to infect a new host.
The creatures are all subservient to the prime host which they protect at all costs, mainly because its death spell their deaths due to a unique mental hive-mind link. A nest is developed with a chamber devoted to the prime host, a chamber for the incubators and a chamber where food is stored. Around this nest, the zombie's attempt to defend that territory while others go out to hunt and gather.
In an extended scene on the DVD, Kylie Strutemyer (played by Tania Saulnier) reveals that the Parasite calls itself "The Long One", because of its great age.