Deathdrop,
Xenomorph,
11 years ago
This is one of those unanswered questions of the Alien movies, since the Xenos grow so ridiculously huge so quickly with no apparent food source.
One of the theories is that they're "extreme omnivores" ie: they can eat literally anything, another says they feed off of kinetic energy generated by moving, another says they just "absorb" nutrition from whatever source is available... You get the idea. No one's really sure.
It's a bit like no one recognizing that Clark Kent is Superman; it doesn't make any sense, but the story needs it to work.