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Over the last 60 years, a new type of bee has slowly been spreading north through the Americas. But these are no ordinary bees.

They’re killer bees. They’ll come over to shake hands with their docile domestic honey bee neighbor, and the next thing you know, they’ve snuck inside, murdered the queen, and commandeered her workers. And once they’ve set up shop, they defend their hives with ruthless violence.

Disturb a killer bee colony and they attack by the thousands, pursuing their enemies relentlessly, raining down a hail of venom-laden stingers. But these bees were never even meant to exist. They’re the result of a lab experiment that failed … and then escaped.

The real name for killer bees is Africanized honeybees, which comes from the fact that they’re a hybrid of two subspecies: the European honeybee and the African honeybee. Africanized bees look almost exactly the same as European honey bees— even bee scientists need to analyze their DNA to tell them apart. But they sure don’t act the same.

The hybrids were created in the mid-1950s by a Brazilian bee scientist named Warwick. Kerr, a mad scientist bent on achieving world domination using an army of deadly insects. I’m kidding.

All he was trying to do was build a better bee for Brazil's honey industry. See, honeybees aren’t native to the Americas — they come from Europe, parts of Asia, and Africa, and were brought here to produce honey and beeswax. While some honeybees have escaped and started feral colonies, they’re essentially domestic livestock just like cows or chickens.

And like any domestic species, humans selectively breed honeybees to enhance desirable traits like honey production or disease resistance. That's exactly what Kerr was doing. European honeybees are great at producing honey, but they weren't doing very well in.

Brazil. They were falling prey to disease and tropical predators. African honeybees, on the other hand, produce less honey, but are better adapted to hot climates like Brazil's, and are more disease resistant.

Kerr's goal in crossing the European and African honeybees was to breed a honeybee that could both flourish in a tropical climate and produce plenty of honey. The only problem? African honeybees are much more serious about defending their nest than European honeybees.

We’re not totally sure why they evolved to be so fierce, but it might have to do with the vertebrate predators that evolved alongside them. Honey badgers do what they want, and if what they want is to rip open your house to eat all your food and your larvae, you'd have to be pretty fierce too. But in Africa, beekeepers successfully keep and work with African honeybees, because they know how to deal with their stronger defensive behavior.

So crossing these bees with the European subspecies seemed like a promising idea. And Kerr's hybrid — the Africanized honeybees — did indeed fare better in Brazil's climate, and they had the potential to significantly increase honey production in the country. Problem was, they were still very aggressive.

And then there was a small, but legendary, lab accident. One weekend in 1957, while Kerr was away, a visiting scientist accidentally released 26 of the hybrid queen bees from the experimental facility. Oops...

The bees established colonies in the wild, interbred with feral European honeybees, and began to spread through South America. Eventually, they reached Central America, Mexico, and the southwestern United States. This was very bad news for European honeybees, because the Africanized bees compete for the same resources … and win.

They’ll also happily murder the European queens and take over their hives. The hybrid bees did actually help increase Brazil’s honey production, but now we have all these super aggressive hives in other places, too. It’s a weird case of one invasive species — or subspecies, I guess — replacing another.

Except we really wanted the original European honeybees to stick around. But hysteria about these so-called killer bees didn’t really get going until almost a decade after they escaped, when Kerr publicly criticized the military dictatorship governing Brazil at the time. In an attempt to discredit him, the government and some of the press started calling the.

Africanized bees abelhas assassinas , or killer bees, and portraying Kerr as a Dr. Frankenstein who had created bees that attacked people on command. The truth is, Africanized honeybees are only sometimes a threat.

An individual bee is no more dangerous than a European honeybee — if you encountered one foraging at a flower, it would be no more likely to sting you. They’re only more aggressive when defending their hive. And even if it did sting you, the venom in its stinger is essentially the same as a European honeybee.

Unless you’re allergic to bee stings, it takes about 1,000 stings to deliver a dose that would be lethal to the average adult human. The problem is that an Africanized honeybee colony is much more likely to sting you 1,000 times than a European honeybee colony. In the decades since they were created,.

Africanized bees have killed about a thousand people, which translates to about 16 a year. The good news is, there’s evidence that Africanized honey bees are starting to chill out. Information from beekeepers who work with Africanized honeybees in Mexico, as well as research on hives in Puerto Rico, suggests they’re exhibiting less extreme defensive behavior.

That may be because they’ve been interbreeding with the calmer European honeybees. But humans have also been exerting some artificial selection by destroying especially defensive hives. Still … you don't want to mess with any honeybee hive, unless you know what you’re doing and have proper protective gear.

Even if it hasn’t been taken over by the zom-bee apocalypse. Thanks for watching this episode of SciShow! If you’re interested in more weird science stories like this one, just go to youtube.com/scishow and subscribe. [ OUTRO ].