This lesion was produced by the bite of a brown recluse spider. The brown recluse is one of two common spiders in the United States considered poisonous. (The other is the black widow.) However, the hobo spider, wolf spider, and jumping spider can also produce bites that require medical attention.
Clark RF, Schneir AB. Arthropod bites and stings. In: Tintinalli JE, Kelen GD, Stapczynski JS, Ma OJ, Cline DM, eds. Emergency Medicine: A Comprehensive Study Guide. 6th ed. New York, NY: McGraw-Hill; 2004:chap 194.