Not many people consider this when they publish there animation of a 3d alien in a forest but the biggest killer on a living planet isn't oftern the sentient life forms that inhabit it, it is the micro-organism. We have been visited by extraterrestrials but oftern they are found with a flu influenza infection or something similar and die within a few weeks not having any natural anibodies in there body for any of the bugs on earth, this includes things like e-colie and other simile things we homosapient humans have adapted to over the few hundred thousand of years of inhabiting earth.

Even most of the simple form of bacteria that we have on the surface of the planet, all though we take them for granted have potential to be a killer infection to any EBE from another world that does have things like body regulation with nanotechnology and cybernetic heath systems. If you wish you can sign up and publish information of bacteria and virus and how we either naturally defend against them or how we produce vaccines for them. This information will be very helpful to any party interest in for exampke dinning with a the Queen of england or meeting to shake hands with the US Presiden in greetings from another world.