yes. we think other species are aliens because we dont know what they are. maybe aliens dont know about us and think we are aliens.
To date no extra terrestrial life has been found anywhere. It is very unlikely that any will be found in our solar system; certainly no intelligent life. It may be the case that one day it will be...
the hideous and ugly Alex Merritt
xenomorph
There is no evidence that aliens exist therefore the biology of aliens, if they do, is unknown