Scientists in the US have figured out how to make normal bees act like their 'killer' Africanised cousins.
Africanised honeybees were developed in the 1950s when Brazilian researchers crossbred European and African bees in an effort to make a breed that produced more honey.
A swarm escaped captivity in 1957, and since then have been linked to deaths of as many as 1000 people, most of them in South America, but there have been reported deaths in the US in recent years.
While smaller and less venomous than normal bees, they attack anyone and anything that gets even close to a nest in massive swarms.
"In a hive of ordinary European bees, about 10 percent will attack if the hive is threatened, but with African bees, all of them attack you," bee hive owner Allen Miller told the Waco Tribune in 2013, after a farmer was stung to death by a swarm 40,000-strong.
Until now, it's been unclear why the bees are so angry and aggressive. The latest research, conducted by the American Chemical Society and the University of Sao Paulo State, suggests it's all in the bees' brains.
They looked at the difference between killer bees and normal bees' brains, eventually focusing in on small proteins called neuropeptides, which act as transmitters. The killer bees had short peptides than the normal bees.
When researchers injected the shorter peptides into the brains of normal bees, they "became combative" - effectively creating killer bees.
There is a point to this experimentation - they hope that by figuring out why Africanised bees are so violent and aggressive, they'll be able to stop the spread of the vicious species.
Last year an Arizona beekeeper claimed to have eradicated killer bees from his hives by removing the queens, replacing them with non-Africanised queens, whose offspring are docile.
New Zealand remains free of Africanised bees.