Sil's Species

The "Species" in the movie Species is an unnamed, aggressive alien species intent on spreading itself throughout the universe by infiltrating and annihilating the intelligent populations of other planets. It is capable of rapid growth and can bond its own DNA to that of other creatures through a number of methods. Most common is by sex, but in the first movie a rat eats one of Sil's severed tentacles and develops Species-looking attributes. They are apparently inspired by the mythological succubus and incubus, who were demons who seduced their victims to have sexual intercourse with them.

Origins
In Species II a professor named Herman Cromwell, played by Peter Boyle, claims that the original species originated in the Large Magellanic Cloud (called the Magellanic Galaxy). The only other place in the universe where Carbon-based life had apparently been discovered. It is also stipulated that they were a "cancerous" race that visited Mars millions of years ago when its surface was similar to that of Earth, and annihilated all life on its surface before leaving a remnant of DNA in its soil, in case something from another planet came to visit so that their species could continue to infect other planets in a similar manner. Then the soil-test taken by the astronauts was exposed to warmer temperatures in the space-shuttle the DNA went active after millions of year in hibernation. It toke the form of a black slime that could move on its own accord seeking suitable hosts. It was able to infect the astronauts and cause amnesia so they later won’t remember being attacked and infected by it.

Mankind's first interaction with this particular species occurred in 1994 when the SETI (Search for Extra-Terrestrial Life) project received a pair of messages from outer space. The first message contained a more efficient use of methane, while the second contained a DNA sequence along with directions on how to mix it with Human DNA. As the first message was seen as friendly contact, scientists went ahead and performed the fusion. Three living organisms were created, two of which were put into frozen stasis in liquid nitrogen, while the third was allowed to grow under the code-name "Sil".

Physical Appearance and Growth
The Species appear to be sexually dimorphic with males being much larger than females. Males are also quadruped with females having smaller bipedal (humanoid) forms and appear to be much more agile. Both genders of the Species have skeletal bodies with their heads being much smaller compared to their bodies, their mouth has two mandibles similar to that of the Predalien and also have hair like mandibles that are similar to the Predator species. There was a noticeable change in the appearance of the males in Species III and the Patrick creature in Species 2, this is only because the host of the alien DNA in Species 2 was infected with the alien DNA so the resulting creature was a pure form of the creature. Both genders have the ability to shape shift between Human and Alien forms and also exhibits a limited ability to morph their alien forms for the purpose of adaptation to given situations. Females are able to manipulate their "hair" as well as retractable spikes on their backs used in combat and their breast tentacles as well. They also have a kind of harpoon-tongue. Males are able to split their heads in two, thus forming a duel headed form and also exposing a long tentacle from between their "heads" which can be used to kill or perhaps impregnate females. One male short-lived hybrid in Species 3 had an extendable tentacle-penis which it tried to move down the females mouth-just like the tentacle described above. This suggests that the female species in fact can get impregnated via the mouth. Every member of this species seems to have at least one kind of natural special- weapon each. The female in Species2 had extend able backspines (since she was a clone of Sil in Species 1 it’s likely Sil also had this ability alas it never was showed). The female in Species 3 hade sharp-pointed head-tentacle how could penetrate a humans skull. The weapons shown in Species 4 includes (in females) sword-like wrist-blades or the ability to spit bone daggers and (in males) a large, extend able "inner-mouth". No species seems to have more than one of this special-weapon. But they have one each. It’s unknown how many variants exist or if they are tied to gender in any way. However, it is unknown whether the Species is patriarchal or matriarchal within its own social circles as a population of sufficient size has never been observed in the movies.

Most of the members of the species seen are actually mutations from humans, but a pure form is seen in the first film. It takes on the form of a blobby, tentacle monster with a long mouth-like appendage that lashed out at whatever was nearby and grew so fast that it would double in size in a matter of seconds. After a little over two minutes of life, it was killed by immolation. A similar creature is born from a female human astronaut infected by the alien DNA in Species2.

In the Film Novelization of Species, the "pure" creature was actually a hybrid between the alien DNA and the DNA of a bat. This was done so that the creature would know no better than to use its natural free form instead of shielding itself behind a camouflage.

The most prominent example of a mutation induced by the species was that of "Sil". The alien imposed its rapid growth on Sil, causing her to form into a visible fetus in a single day and grow into a young girl (with the gender chosen to make her more "Docile", something that got a laugh from Press) on the verge of puberty in a month. She exhibited great speed and strength, but also suffered from terrible nightmares brought on by her alien DNA. Sil later claims that she thinks the nightmares "Tell me who I am".

While on the run, Sil pupates by forming a ball of maroon-colored flesh similar in appearance to the pure alien form. She was horrified by this development and the process appears to be very painful. Even the cocoons are dangerous. They can extend tentacles and devour a human. A female clerk how enter the room ends up this way. After a few hours, she emerged as a fully-grown (and consequently very attractive) adult.

While still somewhat shy and uneasy, Sil is able to quickly adapt to her surroundings, showing an incredible cunning as she blends into society. In Species 3&4 they demonstrate an ability to assimilate knowledge just by touch. They can-for example-in a few seconds assimilate a books entire content just by touching it. How this ability can be put to outer uses have never been demonstrated. Pretty soon, her alien libido takes over and she attempts to mate while in a state of almost constant fertility (she seems to menstruate once). During this time, she demonstrates a strong animalistic survival instinct, regeneration abilities,superhuman strenght and jumping abbility and ability to sense genetic flaws in potential mates. She also kills without remorse when she feels threatened.

Her human form is in truth merely a disguise and her alien form is a hideous mockery of the human form. Her form is chitinous and reptilian, somewhat reminiscent of the aliens from Alien, but more human in appearance. Her hair has been replaced with tentacles which are slicked back and her teeth are sharp. Her breasts, rather than storing fat or mammary glands instead store tentacles which come out of her nipples, she uses them as a weapon but they are also used in a mating ritual (As shown in the second film). This form seems capable of holding its breath underwater for an extended period. The species also seems to have a different array of senses then the five ordinary possessed by humans. They have the ability to sense genetic defects in potential partners. Sil seems to have a "danger-sense" how alerted her then the human agents seeking for her where nearby. They seem to have some kind of telepathic abilities as well. In Species 2 Eve was able to feel that Patrick felt by distance. She was able to locate him and even see through his eyes. Then Patrick noticed the intrusion he could in turn easily locate Eve for mating purpose. In Species 3 the female was able to track her eggs even after they were removed from her body. In the first movie Sil show the ability to feel then a sperm fertilized an egg in her body and thus knew she now was pregnant. Even a blood sample taken from Patric in Species 2 was able to sense his presence and was trying on its own accord to crawl back to him then he was nearby. This may be a part of another of the species abilities: Their extraordinary regeneration-ability. They can regrow severed members in seconds. Patric in Species 2 was able to regrow his entire head after it have been blown off by a riffle.

Her son shows some different traits and after being born less than an hour after conception grows at an incredible rate with limbs growing disproportionately and his spine seeming to grow too fast for his skin to keep up.

Since the boy's alien form was quadrupedal (as opposed to bipedal, like Sil's form) and more 'brutish' in appearance than hers, it is assumed that this must be the common appearance of the males of the alien species.

Technology
In the movie's Novelization it is mentioned that the signal that came to Earth was transmitted through several Black Holes which served to hide its point of origin.

It is unknown what level of technological achievement "The Species" are currently at, however their mentioned mastery of black holes is a testament to their achievements. In the cannon versions of both movies and their novelizations, the Species have no space travel capabilities, however in a rejected Species II script, a space faring vehicle of some kind belonging to the original Alien race is mentioned. It does seem plausible (although not canon) race advanced enough to manipulate Black holes would also have achieved advanced space travel.

In the second Movie Novelization "Species II". We learn that the species had once established a colony on Mars and consumed all of the planet's natural resources before moving on. It is unknown how they got to Mars and there is no mention of space travel leaving it opens to debate. However, a character speculates that the Species could be literally billions of years old. Their capabilities remain unknown but the human hybrids show an ability to learn and absorb information extremely fast and put that knowledge to practical use.