"Killer bees" live on pollen and nectar but harvest more pollen than European honey bees. They are hybrids between African honey bees and European honey bees.
African honey bees were imported to Brazil in the 1950s for crossbreeding with European honey bees in hopes of producing a strain suitable for beekeepers in tropical countries. Some of the African queens were accidentally released and established wild colonies. The hybridized bees have since spread northward. They have been reported as far north as Tennessee but do not tolerate cold winters. These hybridized bees are more aggressive than European honey bees and swarm more readily but are superior honey producers in tropical climates.