The African honeybee had long been known to be efficient, if rather aggressive, when, in 1956, some South American researchers captured 26 African queens and took them to Brazil. Their intention was to selectively breed these queens with drones of the local race, a variety notorious for its Latin temperament. It was hoped that the efficiency of the African bees could be combined with the docility of the Brazilian ones.
Unfortunately the African queens escaped from their cages and bred unchecked with the indigenous bees. The result was disastrous. The new strain of honeybee turned out to be far more aggressive than the original African one, to the extent that potential predators would be viciously attacked, even at some distance from the colony. These "killer bees" soon gained a reputation for killing tethered livestock and even humans. Since 1956 the killer bees have extended their range inexorably northwards at the rate of 100km per year. Having killed an estimated 1,000 people in the 50 years since their introduction, they reached Texas in 1990 and are now established in New Mexico, Nevada, Arizona and southern California.