[Spoiler] Regarding Lamar.

[Headcrab Pie]

Lammar was sent into space. However she made contact with a Combine Capital Ship and was able to sneak abord. Using the ventilation shafts, she made her way to the Command Deck and latched onto "Breen-Advisor" and took control of the ship. As Gordon, Alyx, and Kliner are cornered by multipule Striders and Hunters, the Ship swoops down, raining death down upon the Combine. She self-destucts, signaling the end of the Combine, but not before hopping into an Advisor Pod and launching clear.

 

[kamikazeCow]

That would be an interesting concept. A advisor that got latched onto by a headcrab... the zombine 2?! Wonder if lamar would be able to speak then o.0?

 

[Crash Happy]

She's de-beaked. I thought it was fairly established that headcrab's had lungs, which suggests they need at least some air as does the fact they can drown.

 

[ranmafan]

She's de-beaked. I thought it was fairly established that headcrab's had lungs, which suggests they need at least some air as does the fact they can drown.

Not necessarily lungs... maybe some equivalent though, as some zombies remain submerged under toxic waste for what is conceivably hours without ill effect.

My theory is that Headcrabs can: Store enough oxygen (or whatever they breathe) similar to various crustaceans to last them for a good while in the water. What they CAN'T do is swim, since claws and beaks don't make for good water-displacement, and I suspect what you see in-game is an accelerated process of death by exhaustion because they can't get out of the water. They probably do drown, but it wouldn't be so fast.