What Causes Purple Lump On Inner Thigh?

I just noticed a purple nickel sized bump on my inner thigh that I assume is a spider bite a day or so ago. Today in the shower I popped it and black and blue stuff came out as well as blood. What spider could have bitten me? I m not worried as it s not painful and seems to be healing now.. I just want to know what could have bitten me? (I live in SW Kansas if that helps)