Apparently all spiders in the US are harmless except for black widows and brown recluses. How can you tell whether a spider is a brown recluse? Apparently there is a small violin-shaped mark on the back of the spider. So when you feel a sharp pain and realize that you are being bitten by a spider, allow it to continue so that you can calmly examine its back for violin-shaped marks.
Alas, I did not perform this inspection.
While doing this research on Google Images, I encountered one of the most disgusting images I have ever seen. This rivals the time that Dan had a cyst removed from his arm and showed us digital pics of the gaping wound. Here it is: disgusting spider pic.