Default Monster

Alright movie buffs and cinephiles. I have a question.

How did the dripping, snarling, coiling mother-creature from Alien (1979) become the default monster for all sci-fi horror flicks forever after?

Bad genre film after bad genre film has the same snarling, coiling, dripping body-eating mother-creature at the bloody heart of the story. These creatures all always female. What does that say about the nut jobs who write and produce these things? And they all came from the same rack in Costumes and Species Effects.

Is it simply that there are so many left-over parts in various trucks and crates that you move the one eye from one side of the scaly head to the other and hope no one notices?

Come on, Kids. 'splain me...