My spider female had the same thing! Only her's was almost not noticable. Questions: Can you move it under the skin or is it hard and solid? How does the inside of the mouth look?

I took mine to the vet and he said to swab with diluted Betadine, and gave me some needles to lightly prick it if need be to then to swab over that so the Betadine can get in there. Basically he said it looked like the sight of a small infection (Note: my vet was not a specialized herp vet).

I would take him to the vet first though before self-medicating: just to be safe and to get an expert opinion.