Many ant species bite people, and some species may sting, injecting venom. Imported fire ants are notorious stinging pests in the southern half of the United States. When their mounds (nests) are disturbed, they swarm in all directions stinging intruders. Fire ants have been reported to invade healthcare facilities, stinging residents (some cases resulting in death). This chapter discusses fire ant biology and behavior, sting reactions, and ways to prevent the ants from entering healthcare facilities.