Itchy red bump with black center...bite? skin cancer?

Last week, my husband noticed a small black dot on his leg, resembling a small scab.  He didn't pay much attention to it, until yesterday, when a red mosquito-bite looking bump developed underneath the black dot, and the area around the bump became really hard and swollen. The entire area is now itchy, and scaly? We were moving into a new (but old) house last weekend, and he thinks perhaps it is a spider bite.  I've done some research, and it seems like his symptoms could either be a brown recluse bite, or possibly a skin cancer spot.  Any ideas?