Some guy in London was filming a bumblebee that got caught in a spider web.  And just as the spider was about to kill it, a second bee flew in and STUNG the spider. 

It's not clear if it was just by chance, or if the bee somehow knew his buddy was in trouble.  Anyway, you can only see it when it's in slow-motion.  According to the guy who filmed it, both bees survived.  But he couldn't find the spider.

 Check out the video below! The slow-mo starts around :22