- Alternative Character Interpretation: The alien species that sent the message with the information to create Sil. Was it all an evil plan to exterminate the human population over the Earth and replace it with Sil's offspring as it looks, or it was a genuinely friendly attempt to share biotechnology that got screwed because Finch and company couldn't handle it the right way? (Expanded materials state the former, but the films themselves leave it open.)
- Best Known for the Fanservice: The Species films are mainly known for one thing: Natasha Henstridge (or her equivalents in the third and fourth movies) taking her clothes off a lot.
- Evil Is Sexy: Downright enforced, as the deadly alien hybrids look like supermodels in their human forms.
- First Installment Wins: Even if Species has quite its share of dissers, it is considered relatively well-done and serviceable, in contrast to the increasingly worse sequels.
- Foe Yay: One-sided; due to Sil and Eve's natural instinct to mate, they seem to develop a minor attraction to Preston. However Preston sees them both as monsters that have to be destroyed.
- Hilarious in Hindsight: One of Sil's victims in the first was named John F. Carey. The 2004 Presidential candidate was John F. Kerry, who was a well-known senator at the time of the movie.
- Idiot Plot: Regardless of whether Sil was a failed peaceful contact between races or a wicked alien device to destroy humanity, he first film would have never happened if only Finch and the US government had not been so extraordinarily idiotic in their handling of the Sil project. They start the chain by deciding to terminate her, an experimental subject they struggled a lot to create, only because she had what in any regular little girl would be mere night terrors. They then try to do it while she is awake and painfully aware of it, even although they don't know the extent of her skills in case she tries to resist, which is why they are killing her in the first place. Then it turns out that the security of her containment chamber was non-existent, not to talk about the entire facility, which, aside from being pathetically ease to escape from, also happens to be near some train tracks that lead to a densely populated urban center! But that's not the last, as Baker later deduces they didn't even try to educate Sil in human customs and values, despite the obvious fact that her cooperation would have been desirable, if not downright vital, for their experimental goals. And finally, in order to solve the mess they have caused themselves, they just send a very small and unsupported (and judging for their attitudes, very unprepared) search team instead of calling for an official police manhunt with the pretext Sil was a female serial killer or something similar to keep the masquerade. Really, Finch and his people weren't just incompetent: they were basically asking for humanity to be destroyed.
- Nightmare Fuel: Many of the deaths are brutal (such as Sil ripping the spine of a woman), the alien transformations are as disgusting as the ones from Alien, and even the first movie's soundtrack contributes to a creepy atmosphere, while maintaining a sense of innocence and naievete that makes Sil such a relatable (and thus, all the more horrifying) villain.
- Paranoia Fuel: See Fan Disservice.
- Retroactive Recognition: Michelle Williams as the young Sil.
- Sequelitis: The third and fourth films came about by the two-picture deal with Syfy. The third pretty much comes off more like you would expect a scifi TV show to. Which to some was a far cry from the first two, while others appreciated it. While the director of the third had plans for the fourth, it instead tried to examine a different What Happened to the Mouse? and most would probably agree made a film that made the second and third less bothersome.
- Special Effect Failure:
- The aliens' prosthetics in Species III are vastly inferior to what was seen in the two previous films. The Awakening has similarly bad effects, but for the most part it does a better job of working around them.
- In the first film, the "mist" in the woods outside the hot tub guy's house is patchy, obviously from a smoke machine. Also the CG in the final scenes (which H.R. Giger complained about, saying that unlike the animatronics they weren't worthy translations of his design).
- Strawman Has a Point: Dr. Xavier Fitch says they made the alien female because they assumed she'd be more docile, which Preston finds funny and is actually untrue as female members in Earthly predatory species tend to be more aggressive than males (it's mostly mammals who buck the trend). But by doing so they actually may have bought themselves more time, considering a female only can have one partner and reproduce more or less one by one while a male can have multiple ones at once and impregnate all of them. And considering what we see of the clearly more dangerous male hybrid in the first sequel, he turns out to be pretty close to being entirely accurate. Basically, Right for the Wrong Reasons.
- Visual Effects of Awesome: The original has impressive prosthetics, and well done morphing effects (specially in contrast to the dodgy CG in the climax). The sequels, less so.
YMMV / Species