How long does itntake for a spider bite to heal?

That depends mostly: On the type of spider and the health of the person bitten. If you have a brown recluse spider bite that goes down into muscle it could take months to heal (or longer for infection or other complications).

Staph Infection: Please do not just sit at home with a lesion that looks like a spider bite. These often turn into staph infections, and in my practice, a majority of them have the dangerous methicillin resistant staph (MRSA) infection. This very likely needs to be incised and drained or at the least treated with antibiotics urgently.