I'm sure this is a dumb question, so I guess it makes me dumb, but in the "Currently Active Users" it says members, visitiors, and spiders?
Not dumb at all. Spiders are web robots that "crawl" websites to index their content http://en.wikipedia.org/wiki/Web_crawler
Well son I think you're old enough to know the truth. You see when a bot loves a forum, well.....ask your mom.
They are usually found co-habitating with FeedFetchers,FeedBurners and Slurps . I hope that answers you question.
If you are a male spider you will probably will die after mating with the female who likes to eat the male after breeding. At least you will have a smile in your face