“Killer bees,” properly known as Africanized honeybees, are not more poisonous than other honeybees.
They are, however, much more aggressive than the gentle European honeybee when they feel threatened or encroached upon, and are more likely to kill people or animals by bombarding them and delivering multiple bee stings.
There’s a reason behind this aggressiveness. Conditions in Africa are rather harsh compared to the soft, moist climates of Europe and the Americas. To compensate for an environment that often has little food and water, these bees developed a higher level of aggression and the ability to produce a whole lot of honey on short notice.
That high-volume honey production was too good to pass up for apiculturists (beekeepers). In 1956 a geneticist named Warwick Kerr brought African honeybees to Brazil in an effort to crossbreed them with more docile European honeybees.
His plan didn’t quite work so well, his bees and their offspring never eased up on their aggressiveness. Worse, they escaped from captivity and started displacing the gentler honeybees.
South American beekeepers simply got used to working with the more aggressive bees by taking greater precautions and using thicker bee suits.