I read the excellent article by Troy Major, MD, on the treatment of 20 patients with brown spider bites. I was reminded of a simple bed side diagnostic method to diagnose the bite of a brown spider. Skin temperature is related to arteriolar circulation, while skin color is related to capillary circulation. The toxin of the brown spider constricts the arterioles and dilates the capillaries, therefore the bite results in a cool erythema.
The examiner touches the erythema and compares it to the surrounding skin. If it is cooler, you have a brown spider bite. If it is warmer than surrounding skin, you look for another spider or an insect bite.
This simple touch test may avoid extensive and expensive treatment. As an aside, the arteriolar damage is the cause of necrosis.