Seeing as we don't know if there's a substance that ALLOWS the TFAW mechanic to even TAKE PLACE, I'm not assuming anything. A facehugger has a carbon interface to glomp carbon lifeforms which COULD be a weakness. An Adult may not, especially if it doesn't have tasty carbon to begin with.
Secondly, Predators have some serious catalytic fluorine action going on. For all we know Pred sweat is completely 100% lethal to the TFAW.
Same for Aliens, a species that is compatible with Dogs, People, Jockeys, and Preds... that's pretty goddamn virulent in it's own right. Jockeys don't even seem to have the same setup as the two terrestrial morphologies in particular. For all we know Jockeys designed/stole Aliens to EAT the TFAW. Fire sure as hell kills the TFAW, it doesn't kill Adult Aliens. Thinking the Narcissus Engines would turned the things into kentucky f**ked virus.
Doesn't seem quite so cut and dried.
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I think bagging an organism that constantly changes its basic cell structure would be something worth bragging about
Would that be what goes next the dread Invisible Stalker?
"No Seriously, I totally like pinky swear on my tusks it's not
actually a parakeet, its a...
space monster... no really."