Africanized honeybees—the term entomologists prefer rather than killer bees—are a hybrid originating in Brazil, where African honeybees were imported in 1956. The breeders, hoping to produce a bee better suited to producing more honey in the tropics, instead found that African bees soon hybridized with and mostly displaced the familiar European honeybees. Although they produce more honey, Africanized honeybees (Apis mellifera scutellata) also are more dangerous than European bees because they attack intruders in greater numbers. Since their introduction, they have been responsible for approximately 1,000 human deaths. In addition to such safety issues, concern is growing regarding the effect of possible hybridization on the U.S. beekeeping industry.

In October 1990, the bees crossed the Mexican border into the United States; they reached Arizona in 1993. In 1996, six years after their arrival in the United States, Africanized honeybees could be found in parts of Texas, Arizona, New Mexico, and California. As of 2009, Africanized honeybees are also found in Nevada, Utah, Oklahoma, Arkansas, and Louisiana. Their migration northward has slowed partially because they are a tropical insect and cannot live in colder climates. Experts have suggested two possible ways of limiting the spread of the Africanized honeybees. The first is drone-flooding, a process by which large numbers of European drones are kept in areas where commercially reared European queen bees mate, thereby ensuring that only limited mating occurs between Africanized drones and European queens. The second method is frequent re-queening, in which a beekeeper replaces a colony’s queen with one of his or her own choosing. The beekeeper can then be assured that the queens are European and that they have already mated with European drones.