Odd experience with a garden spider

I haven't had any hands on experience with spiders other than Jumpers (love them!) And Crab Spiders.

I've been taking care of someone's house this past week and they have a pool.

I've been checking the pool skimmers daily for frogs and whatnot, but there's usually a handful of garden spiders on the inner edges unable to crawl out. The first one I rescued was floating in the water, the poor thing frantically swam and practically jumped on my hand as soon as I reached for it, who knows how long it had been out there.

But the second one I rescued sat on my hand for a while and cleaned it's legs as I watched. After it thoroughly cleaned all it's legs, it slowly unveiled it's fangs and easily sunk them into my hand. It tickled more than anything but I don't like the idea of being bit, so I shook my wrist so it fell off. This spiderbro just looked so offended by what I had done as it looked at me, but it turned around and moseyed away.

I was completely relaxed while watching it, so it's not like it felt threatened (it didn't act like it either.)

Anyone know what it was doing and why?