Hi,
yes I've had spider bites. Most of them are just a little itchy with a small raised area. One time I got one on my arm and the next day it was twice the size, with a raised scab and I didn't even scratch it. The doctor said it was a spider bite and sometimes the venom can get in - it has enzymes in it. This acts to break down the tissue, hence the scab. When a spider bites a fly the venom pre-digests the fly so the spider can eat it. I'm sure that was a scientific explanation you could do without LOL. You could try dabbing it with alcohol and then put some benadryl cream on it or cortisone cream. If it doesn't improve then go to the doctors.