What's the origin of Headcrab's variations?

[Sandvich Enjoyer]

In Half-Life 1 we only see basic headcrab (and Gonarch, but that's just very big basic headcrab), but in Half-Life 2 we see more types of this species- Fast and Poison Headcrabs. Both games are set around 20 years from eachother and I'm not entirely sure if hedcrabs could evolve this fast, so I think that Combine had something to do with this.

[TamTroll]

my best guess is they're natural variations, but we just didn't see them in the first game. maybe they came from a different region of Xen, and that region just never opened portals to Black Mesa.

[Sandvich Enjoyer]

Originally posted by TamTroll:

my best guess is they're natural variations, but we just didn't see them in the first game. maybe they came from a different region of Xen, and that region just never opened portals to Black Mesa.

To be honest, headcrabs are most curious species for me

[MrMcSwifty]

I thought it was official lore that they were genetically modified bioweapons created by the Combine?

[WhoIsSpino]

the combine genetically modified some headcrabs to become poison, and fast headcrabs, but also to not transform into gonomes after a couple of hours, so that they could easily handle headcrab problems even if it gets out of hand.

[Ghidrah1]

They look like older versions of the teeny ones the Gonarch spewed out at Gordon on xen

[Reeva!]

Fast headcrabs are too vulnerable, they get mulched by anything their own size. The only reason they'd evolve like that (assuming the normal headcrab is the baseline) is to hunt smaller, faster prey, but they're too aggressive to be scavengers. Musta been engineered, what they do to humans is very useful to the combine. From what we've seen though, they do hunt in packs, they're never alone, but sometimes they engage stupidly, one at a time.

Poison headcrabs, idk. All headcrabs have toxins, but the other 2 don't inject until they couple with your head. It's really slow, but bulkier than the other 2, and rather loud. I'd have to say modified by the combine. Once they get entrenched into a human settlement, they're really hard to get out, cuz they make some gnarly zombies.

What bothers me about them is that they also attack the Combine. They can modify human brains and yeet them into gigantic constructs that can follow orders unquestioning, like a regular soldier. Why they would not force headcrabs into being loyal is weird to me. Maybe they're just too slow and weak to bother that much.

I just assume anything used by the combine has to be modified. They love that ♥♥♥♥.