I was working outside, when suddenly my inside forearm began to sting. Upon pulling up my sleeve, I noticed a red dot at the source of the stinging. About 30 minutes has passed, the stinging has diminished, but the dot has become about 1/8 inch long, surrounded by a welt slightly larger than a pencil, smaller than a dime. There is also redness about the size of a half-dollar. Have any idea what could have stung/bitten me? I live in Missouri.