Premise: Bordering on Japanese tentacle porn, the Species franchise is sexually charged sci fi-horror about scientists who combine alien DNA with human and have to deal with the fallout when the sexy hybrid escapes and begins seeking human mates, killing those who don't meet her high standards.

Warning: spoilers ahead!

1. Species (1995)

Government scientists using radio telescopes to scan space for signals from aliens receive a message containing information on alien DNA and how to combine it with human DNA. Suckers that they are, they follow the instructions and successfully injected into three human ova. They freeze two (Can you say "trilogy"?) and allow the other to grow -- rapidly, appearing to be a 12-year-old girl despite growing for only three months. They name her Sil. Fearing what they'd created, the team decides to kill her, but she breaks free and runs off, boarding a train to Los Angeles. Team leader Xavier Fitch gathers a team of specialists to track her: molecular biologist Dr. Laura Baker, anthropologist Dr. Stephen Arden, psychic Dan Smithson and mercenary Preston Lennox. Now grown to full size, Sil seeks to reproduce by seducing men but is always interrupted by player haters. Using a disguise, she seduces Arden successfully and kills him. The others give chase into the sewers, where Fitch is killed. Now pregnant from the tryst with Arden, Sil gives birth to what appears to be a toddler boy...with a prehensile tongue and a taste for rats. Smithson kills the baby alien, and Lennox blows off an angry Sil's head. In the end, we see a rat chewing on one of Sil's severed tentacles and somehow mutating into a hybrid rat-alien. Makes sense to me.

2. Species II (1998)

A couple of years after the events in the first film, a team of three astronauts -- Patrick Ross, Dennis Gamble and Anne Sampas -- make the first manned mission to Mars. Ross gathers a soil sample that, unbeknownst to him, contains an alien life form. As the ship blasts off to return home, the black gooey entity lurches at the crew, causing a seven-minute break in communication with Earth. When communication is restored, the astronauts have no memory of what happened during those seven minutes. Meanwhile, on Earth, Laura Baker from the first film has continued Fitch's work, developing one of the other two frozen ova that were injected with alien DNA. She names it Eve. Back on Earth, Ross then kills a scientist at the lab testing the soil samples, in order to hide the alien evidence. When samples taken at the crime scene reveals hybrid human-alien DNA, Lennox is recruited to help Baker track down the culprit. They locate Sampas just as she gives birth to an alien following sex with her husband. They kill the alien, but not before it kills the astronaut and her husband. They find Gamble, but he hasn't been infected by the alien, so he joins them in the search. They track Ross, who is making his way around the area impregnating every woman he can bed and stashing his offspring in a remote family vacation home. Since Eve has a psychic connection to Ross, they use her to locate him. As they mate, the team tracks them down and kills the cocooned offspring with a concoction using Gamble's sickle cell-tainted DNA before they have a chance to mature. When they approach the mating aliens, Ross attacks Baker, and Eve defend her but is killed by Baker. The team uses Gamble's blood to finish off Ross, but as Eve's body is taken away in an ambulance, we see one of Patrick's alien boy offspring in the vehicle observing Eve as her stomach expands with an alien baby.

3. Species III (2004)

Picking up where Species II left off, as the medical transport drives away with Eve's body, she awakens and gives birth to a baby alien, only to be killed by Ross's alien boy offspring. The driver of the ambulance grabs the newborn baby and runs off. It turns out he is Dr. Abbot, a biochemistry professor at a local college who wants to save the alien species. Under Abbot's care, the baby grows into a young woman named Sara. Full grown, the alien boy tracks Abbot down looking for Sara. The boy is sick, however, and immediately dies, but not before revealing that there are other alien hybrids ("half-breeds," as Abbot calls them) who are likewise sick. Sara, venturing out to seek mates, discovers that all of the hybrids are sickly. She, however, has "superior DNA," and Abbot injects alien DNA into her eggs with the intention to reproduce healthy hybrids. When a half-breed kills Abbot, his student assistant Dean doesn't want to continue his work, but Sara teams with a female half-breed named Amelia to try to force him. Dean grabs the ova and flees to a power plant, where Amelia attacks him. Sara defends him and kills her. A few weeks later, Dean agrees to create a mate for Sara, but only he knows that he made the male sterile, ensuring there won't be any offspring. I guess that means no Species IV...

4. Species: The Awakening (2007)

Here we go again. Now that the planned trilogy has ended, we begin a whole new plot. Miranda Hollander is a college professor who has lived with her Uncle Tom since her parents died. When her alien side emerges one day and kills several people, the truth comes out: Tom isn't her uncle; he created her by combining human and alien DNA (the third frozen ova from the original film?), but he had second thoughts about the experiment and took her away with him, raising her as a human by injecting her with human hormones while she sleeps to keep her alien side at bay. She's gotten sick lately, however, so Tom takes her to Mexico seeking help from Forbes McGuire, with whom he teamed to create Miranda. They find McGuire living with a hybrid named Azura. He's a modern-day Dr. Frankenstein, creating hybrid "clones" of dead people for loved ones. He examines Miranda and says she's near the end of her lifespan, and the only way to extend it is to kill someone and inject her with the fresh human DNA. Both Tom and Miranda balk at the idea, but when Miranda falls ill, Tom kidnaps a woman, and McGuire transfers the DNA into Miranda. She heals physically, but her alien side starts to become dominant, killing people right and left -- including McGuire, though not before she has sex with him. Tom discovers that Miranda is pregnant, and in a moment of clarity, she asks him to kill her. Before he has a chance, Azura attacks, blaming them for ruining her good situation, and Miranda kills her, suffering a fatal wound in the process. Tom opens several gas tanks in McGuire's lab and blows up the building up as he walks away.