Gina (Pueblo, Co) on 04/05/2015:

A brown recluse bite will begin to blister and turn purple/black around the bite within a matter of minutes to hours. The black area is usually quite large (1-12 inches across- not usually as small as 1/4 inch) and indicates the area that is being affected by the venom. This is not infection, so antibiotics will have no effect on it. The venom acts to kill the tissue, which will slough off in a layer or chunk, leaving a large open wound. The various remedies mentioned in this post include various items that purport to draw out the venom. The most effective of these, I have found, is the potato poultice.

The easiest and most effective method I have found is to use a starchy potato (Russett, Idaho, or the like. Do not use a waxy potato, like a red or gold potato). Peel the potato or scrub it to get the dirt off. Use a grater to shred the potato like you are making hash browns. Take a handful of the wet potato shreds and place them into a piece of thin cloth, like a handerchief and tie it shut (use a rubber band or twist tie). Use a bit of alcohol on a cotton ball and scrub the bite to break the blister open and disinfect the surface. Place the potato filled cloth on the bite and secure it in place by whatever means necessary. Leave on for several hours, until the potato begins to dry. Discard the old potato where it cannot be eaten by any animals (it can kill them) and repeat with fresh potato. You should notice the purple area fade and get smaller until it is gone, over the course of a day or two. Keep repeating until the purple is all gone. If you stop early, the remaining purple may still slough off. If you see streaks of red, it indicates infection as well as venom so you may need to see a doctor.