Slicy Alien Horrors.

[TimeWizard]

Gentlemen, Ladies, I've called this meeting to discuss an ominous trend. A trend that threatens our very lives. The number of slicy alien monstrosities is too damn high. You know what I mean: Tyranids, Xenomorphs, Zerg. Flood, Head Crabs. Sliver.

Scythy bio bad things.

Joking done, I just noticed that this is like some kind of Jungian collective image. Why do we have so many things that are, essentially, modified versions of the same template? They are mindless, or hiveminded. They harvest bio matter. They swarm in packs. They have bladelike appendages. The word Evolution is tossed around a lot. Acid is a prominent feature. They are often opposed by a technologically superior but numerically inferior enemy. And humans. They came from outside the Galaxy/Plane. They Have A Queen.

Seeing a Pattern? Are they all modeled off each other or some older example I missed? What Gives?

[Cerlis]

its because all those things are the accumilation of many things that scare people.

Whats worse than a psycho alien? One that cant be reasoned with (simple hive mindish, but intelligent)

Worse? Ones that swarm, a complete feeling of being overwhelmed.

Worse? When they dont kill you but take you to be fed, bred with or mind controlled by their leader (reminds me, i think you forgot the bugs from starship troopers)

Worse? When they are earily familiar (bus, lizard like) but so alien, and uterly deadly(hence spikes or blades).

Worse? Poisonous. Acid is a variation there of.

[Tavar]

I think Acid is used because it feels like something that can't really be defended against: it just eats through things. Now, this isn't really true for real life acids, but since when has reality been a factor for popular conceptions?

[TimeWizard]

I get that they are scary, but why are there so many oddly specific repeated combinations ?

Also good catch on S.T.

[Tavar]

A hivemind of things very much not like us is scary. The easiest thing that is both not like us and still recognizable is the insectoid form. That's 2 down. The bio-matter thing is simply the fact that they need a goal, and a very simple one is that they want to eat-hence the harvesting. Blades and Acid are both things that we can associate with biological systems easily, and can also be dangerous.

That's pretty much it.

[Cespenar]

I think the main issue with those types of aliens is the "hosting" process. Which means, they use your body to reproduce. Being the self-aware specie that we are, we value our physical body almost as much as our mind, so the thought of it being violated is inherently squicky to us. The "blades" and "acid" and stuff are simply easy ways to up the threat factor. The real squick is the reproduction.

[Arcanoi]

As to why they're so similar so often, every writer is a damn dirty cheater. Humans can't really avoid being influenced by media we consume. Who did it first? Probably Giger. Giger's crazy sexualized abstractions of the human life cycle and body were wildly successful in Alien, mostly by taking things that we recognize in them and subverting or removing them. Consider that babies technically subsist as parasites for their first nine months of existence, and how the Alien resembles a human skeleton. Crazy people are pretty innovative, I guess.