black lump on side of heel

I've had this lump on the side of my heel for about a month and it's not going away. After spending four years in the MC, you tend to look past little issues and stay as far away from docs as you can. But my wife saw it and flipped out. The bump is just bigger than a penny and protrudes slightly from the foot. It's black underneath and painful if I apply pressure directly to it. I've tried digging into, but had no luck. It's not a blood blister and doesn't look like a wart. The house I live in at the moment is in a rural area where spiders and mice seem to sneak around. I'm curious if its a bite or if there's something in my foot that I'm going to have to cut out. Any input is greatly appreciated.