There are a ton of alien movies. Good aliens, bad aliens, ambiguously friendly aliens... the movie industry has covered them all. It's worth noting, however, bad aliens are everyone's favorite.

When we look into the sky and imagine aliens visiting we don't imagine E.T. or A.L.F. or Paul, the pot-smoking alien voiced by Seth Rogen. No, those aliens are cool and all, but most of us imagine alien invasions. We imagine world-destroyers and conquerors because, well, that's human history. 

Scary aliens are fun to imagine and scarier to see. In movie history there have been countless versions of alien visitors and they range from frightening to hilarious. We'll be concentrating on the former. What makes a scary alien? Look ahead and we'll discuss the prototypes. These are the scariest movie aliens ever: