It depends. Some aliens are prob very similar to life on earth. The ones flying around in ufos are probably closer to extra dimensional beings. Whether or not they also exist at a slower vibrational speed, idk. If so they prob poop...Perhaps they are even us in the future, or our own thoughts projected out into the universe.
the ones in ufo's might just be robots. Easier to send a purpose built AI across the universe than a being that spent millions of years adapting to a single ecosystem. the second one you would have to bring the ecosystem with you.