That's an interesting question, and there are many, many answers. Truthfully, we don't know for sure, because we haven't met any real aliens that we know of, but there are a lot of theories by authors and regular people. Here are some of them:
There are no aliens that we even know of. So, no.
The aliens dont actually breath, their not even alive, Its all to make money
if its breathing, and you know this by the steam on the lid of the pod. the breath steam is not wet, it is just vapour, but condensation can also form, which is wet and you need to get rid of it otherwise the water will drip onto your alien and the goo and both will die if it keeps happening.
if you see steam then it is alive but do not put it in your pocket because then it will not be able to breath so and if you do not see steam then it is dead so that is why
THE best alien of ben-10 ultimate alien is alien x.
Depends on which type of alien it is. ET alien? Super 8 Alien, Independence Day Alien?, or is it Alien 1-2-3 Series Alien?
Alien.
Alien , Aliens , Alien 3 and Alien Resurrection .
There are 4 alien films: Alien, Aliens, Alien3, Alien resurrection
Alien x is an alien which can travel backin time.... that's all i know about Alien X.
Alien X
queen alien is the best