Hollywood movies have been making us scared of anything for years....sadly our first instinct is to kill  whatever we don't know...eventually they would wipe us out,(reply>), Our food chain evolved from creatures developing new ways to intake external energy...this might sound crazy but we sit at the top of this huge food chain that on another plannet doesnt exist...and to make energy creatures just need there own space and resorces like plants with photosynthesis to produce there own energy...they might need a new planet because of overpopulation ect but we could be literally the thing of nightmares because of our natural evolution....the opposite is likely true also in that we are so basic and un adapted to kill by comparison we are pathetic or just breeding hosts like on alien lol