Elevator Fight SNL Theory Triggered by Spider

5/18/2014 7:19 AM PDT BY TMZ STAFF

The catalyst for the Solange/Jay Z elevator fight has been a mystery ... until now.  "Saturday Night Live" spilled the beans  ... an errant spider.

It's pretty funny ... especially Maya Rudolph who plays an epic Beyonce.

The way they explain the kicks is especially hilarious.