Africanized honey bees (also known as "Africanized bees" or "killer bees") are descendants of southern African bees imported to South America in 1956. Brazilian scientists were attempting to breed a honey bee better adapted to the tropics. Unfortunately, some of the bees escaped quarantine and began breeding with local Brazilian honey bees. Since 1957, pure African bees and their hybrid offspring, the Africanized honey bee, have vigorously multiplied and extended their range throughout South, Central, and North America at rates frequently exceeding 200 miles per year.