I have been bitten by a brown recluse. It was on my leg... I noticed it the first day, looked like an infected hair with a white spot in the middle. kept waiting for it to fester like a zit so I could pop it. NEVER did! White spot kept growing and it developed a hole. The white spot was dead flesh you could scrape away.
Went to the doc. gave me a shot, 2 different pills and some topical ointment. We finally got it stopped when it was about the size of a 50 cent piece.
If it popped, then it was a boil but not a spider bight!