The venom of a brown recluse is a hematotoxin. The toxin causes vasoconstriction of the area around the bite, cutting off blood flow and causing necrosis. The venom also causes platelet aggregation, which forms clots in the vessels around the bite, and hemolysis (breaking of red blood cells). Still, 90% or more of bites heal without a scar.
Bites are graded in a similar way as hematotoxic snake bites.
Grade 1 - no symptoms.
Grade 2- there is erythema (redness),and edema (swelling)
Grade 3- necrosis (some death of tissue), healing will leave a scar
Grade 4- systemic effects are present, such as fever, chills, nausea/ vomiting, weakness, and rash. There can even be worse effects, such as generalized hemolysis, DIC (disseminated intravascular coagulopathy), Rhabdomyolysis (protein in the urine, clogging the kidneys), renal failure, and pulmonary hemorrhage The bite is potentially fatal to small children.
The initial bite can be painless, but within 2-8 hours a lesion can develop, with induration, and a cyanotic ring around the area, showing lack of blood flow. This can progress to eschar formation (dark dead tissue) in 4 days or so.
There is no antivenin for a brown recluse bite. The treatment is supportive care for symptoms, and possible hyperbaric oxygen treatment to the wound, to promote blood flow.
'Critter bites' are covered in AHA's First Aid course.