The progressive spread of the pugnacious venomous imported fire ant throughout the southeastern United States over the past 60 years has caused major effects on farming and wildlife, including decimation of some ground-nesting birds and other species (1–2). This spread has been aided by the increase in fire ant densities and mating flights and by the movement of infested plants and other agricultural products to uninfested areas (2–4). The ants arrived from South America through the port of Mobile, Alabama, in the 1930s, and they now infest more than 310 million acres in the United States and Puerto Rico (Figure 1). Colonies have recently been found in Arizona, California, New Mexico, and Virginia. The ultimate range of the ants is unclear. Other factors have promoted human contact with fire ants. The urbanization of the United States, especially in the Sunbelt states, has facilitated the expansion of fire ants that thrive in disturbed habitats, including sites of new construction. In 1973, polygyne fire ant colonies (multiple egg-laying queens in a single colony) were noted (5). This adaptation has resulted in densities of 200 to 600 fire ant mounds per acre, with 100 000 to 500 000 ants per mound in some areas (2, 6–7). Attack rates in endemic areas, including New Orleans, Louisiana, and San Antonio, Texas, now exceed 50% of the population per year (8–9). In one study (9), 51% of previously unexposed medical students were stung within 3 weeks of arriving in San Antonio, Texas; 16% of these students developed IgE antibody specific for fire ant venom.