A little bit of research turns up the fact that the skin bitten can become full-depth necrotic

Clearly, nobody else has repeatedly clicked Philip's link to the picture of the brown recluse bite.
People! The initial page is just Day 5.
If you have the stamina to follow it all the way through to day 10, you will see why it is extremely important to seek treatment for one of these bites.
You may also lose your lunch. Not for the squeamish.