Yes...and no.SillyBear said:Also - Mr OP is correct. Just because a species may be capable of arriving at Earth (whether through space travel as we know it or not) does not mean they would necessarily beat us in a conflict. You are all just saying that because thats what we grow up imagining - but there is nothing to be certain about at all.
Assuming the aliens are travelling in spaceships, and these are both large and capable of pretty good interplanetary (not interstellar) speeds, they have the capability to make a mess simply by crashing one of them into our planet. They don't need any science beyond that.
Of course, that they travel like that is not a given, but it seems to be the way aliens are getting here in most people's discussions.
Alien wizards using Greater Teleport, no way of telling though.