system
Given the following post, respond as if you're commenting on Reddit:
human
[Alien Universe] How long would a Xenomorph population survive on Earth before killing all other life forms, thus exhausting their sources of host animals?

Once they run out of hosts, do the Aliens die off and become extinct, or do they hibernate in their eggs until some poor saps come along and wake them up?
gpt
We know they can hibernate for centuries at a time in egg-form, presumably they can manage something similar in their regular forms. Humanity would be consumed inside of three years, total extermination could take up to a century - birds aren't hugely easy to kill for Xenomorphs.

Xenomorphs appear to breathe underwater just fine, operate in huge pressures or hard vacuum, so we can say there are no real barriers to their spread. They're the the perfect killing machine - a population starts out in the middle of bumfuck nowhere, Siberia. Reports of strange beasts in the country side spike with disappearances at the same time. Putin blames Obama for deploying his super-special part-animal commandos, since Americans are not real men and require being part black nightmare in order to fight in Glorious Russia.

By the time Russia realises what's going on, its too late. Nuking the hives won't work, because one single alien will survive and eventually become a Queen again, starting the process over. At this point, some have boarded ships. Others started swimming. Russia is the epicentre. They enter Greenland and Alaska quickly, spreading through Europe and America almost at the same time. England quickly falls to infection and invasion, the Xenomorphs taking the channel tunnel or following the seafloor lines, having learnt that, hey, those lead to dinner. Eventually Hawaii'i is the only place left, and even it falls eventually as the ravenous xenomorphs swarm, seeking new hosts.