Top definition
1. When sitting in a park and your friend discovers a spider approaching your lower back going for your bum. This spider could be aiming to actually get inside your bum, therefore becoming a bum spider.

2. An imaginary STI where if you have anal sex too much, spiders will become attracted to your bum, then being able to be passed on to someone else who has anal sex with you.
Helena: "DAMN there's a spider going towards your ass!"

Doug: "SHIT damn bum spiders!!"
by HelenaLexxiFoxxx September 28, 2010
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