What does a spider bite look like on bottom?

Depends : On the type of spider, and ther are only 4 genera of spiders in the us that are dangerous to humans but generally, there may be 1 or 2 small puncture wounds in the center of a red, warm, swollen, initially painful (sometimes) but then sometimes itchy area. There may occasionally be some numbness in the area also. However, black widow bites and brown recluse and hobos can be quite different.