Maggots are efficient consumers of dead tissue. They munch on rotting flesh, leaving healthy tissue practically unscathed. Physicians in Napoleon's army used the larvae to clean wounds. In World War I, American surgeon William Baer noticed that soldiers with maggot-infested gashes didn't have the expected infection or swelling seen in other patients. The rise of penicillin in the 1940s made clinical maggots less useful, but they bounced back in the 1990s when antibiotic-resistant bacteria created a new demand for alternative treatments. In 2004, the U.S. Food and Drug Administration approved maggot therapy as a prescription treatment.