I have a spider bite near my balls?

Last night I slept on a little mattress on the floor. I was fully clothed and had a pretty heavy blanket on. This morning I woke up and had to itch down there real badly. Now there is a small red bump. I don't think there are many poisonous spiders around here. So I read that a spider bite can cause skin to rot. Maybe I should just put some Benedryl on it and keep an eye on it?