There's no way to know if he came across a spider; they're everywhere. However, my boxer isn't having any trouble.
We didn't notice it until a week ago or so; we saw blood through his fur. As soon as we noticed it we cleaned the area with alcohol and mild antibacterial soap. It wasn't nearly this bad at the time (just looked like a scratch/cut). We watched it closely and noticed that he wanted to continually scratch it so we got him a "lamp shade" to protect him from himself. He wore that for about 4 days and today's the 5th. It smells "funny" but doesn't smell like gangrene/flesh rot (I would've recognized the smell from my experience with cows on the farm).
We're taking him to the vet tomorrow but we were just wondering if anyone else had any ideas.