Why did the fly fly?
Because the spider spied her!
Why did the fly fly?
Because the spider spied her!
Alright listen up buttercup, this one is so easy even you should get it. The joke is that "spied" sounds like "spider". Flies don't want to be eaten by spiders, so the fly flew away because the spider saw her. You probably thought the spider was just being friendly, didn't you? You're so innocent it's almost cute. Almost.