How do bees become Africanized?
There are many different varieties of honeybees (Apis mellefera), and any of them can hybridize if they are put together. While there are native bees in the Americas, the honeybees that are kept for pollination and honey production are all imported. The most common variety is the European honeybee. These bees are pretty hardy, but they are best adapted to cooler climates that one finds in the tropics. Their honey production and the stability of the hives is lower in the hotter areas of the Americas.
In the 1950s, a biologist named Warwick E. Kerr, tired of merely being a guy with a cool name, decided he would interbreed bees from Africa that were adapted to a hot climate with honey-producing European bees. He was working in Brazil, and he figured that he could benefit from the combined traits of these two bees: the large capacity for creating honey of the European bees, and the heat tolerance of the African bees.
The bees that Kerr created were good at tolerating heat. They were also more aggressive than European honeybees, more likely to swarm, and more persistent in pursuing invaders. In fact, they can chase an animal a quarter of a mile. This is pretty good stamina (although you can still outrun bees if you keep it up for long enough - click here if you don't believe me). Kerr managed these hives as an experiment, and he did not intend for them to be set free in the wild. He put a special type of screen on the hives called "queen excluders" on the hives. These are meant to allow the worker bees to enter and leave the hives, but hold the queens and drones - who are larger - in the hive. This will keep the hives intact and prevent swarming. Somebody removed the excluders, and 26 colonies swarmed and started to spread.
Since the bees were quite suited to the tropical heat of Brazil, they started to spread. Due to their aggressiveness, people became afraid and started calling the Africanized honey bees "killer bees." There was a lot of sensationalism about the possible spread of Africanized bees, including a popular movie in 1974 called Killer Bees. It is still common to hear people use the term "killer bees," although most bee experts object to the term. Africanized bees are more aggressive than regular honey bees, but bees who do not feel threatened are not a danger to anybody. There are definitely precautions you should take around bees - particularly near their hives - but you have probably seen hundreds of Africanized bees without incident.
Africanized bees did spread, and they are quite common in the southern United States. Exactly how common they are is a matter of some debate. A recent study in California showed that among managed colonies, 13% have DNA of African bees, while the percentage of non-managed bees who are at least partially Africanized is over 60%. Thorough research has not been done on bees in Arizona, but most bee experts believe the percentage will prove to be higher here.
Africanized bees have likely reached their northernmost boundary by now. They thrive in places with mild winter temperatures because they do not store enough food to make it through a long, cold winter. In places like Arizona, though, it is likely that bees will increasingly show Africanized traits because they are so suited to hot climates.
Bees become increasingly Africanized in three different ways:
1. Existing hives will swarm and form new colonies;
2. Their drones will interbreed with European honeybee queens;
3. and they will take over existing honeybee hives.
This last method is fascinating, and it was only recently discovered. Africanized bees can go into an existing colony, kill their queen, and replace her with one of their own queens.
Each colony of bees has its own personality, and there are Africanized colonies that are relatively docile. Since Africanized bees are so well adapted to our environment, maybe the best way to deal with their increase is to replace hostile queens with less aggressive ones. The colony will quickly take on the personality of their new queen.