This patient has a brown recluse spider bite to the leg.
Most bites do quite well, but complications do occur.
Most common is a non-healing ulcer, particularly when they are over fatty areas of the body. The best therapy for an ulcer is to let it demarcate and then perform a delayed skin graft. Systemic symptoms such as headache, vomiting, fever and myalgias occasionally occur. Methemoglobinemia and hemolysis rarely occur. The best treatment is these is probably watchful waiting.