I've been bitten twice, once by some kind of brown spider and once by something I thought was a large ant, but the skin reaction was more like a spider bite. The brown one just made me itch - but the bite occurred while I was driving! I was crossing the river at the time and felt a little prick. When I reached to scratch what I thought was just an itch, the spider scurried out!
I was on my way to swim and somehow it had made it's way under the edge of my suit near the shoulder strap. Fortunately, nothing really happened other than the skin itching, but it continued to itch for weeks afterward. The second bite, on my ankle (I was in a small park the size of a city block), caused necrosis and took ages to heal. It was a few years ago, but I still have a scar.