Honey bees are often praised for their gentle nature; they only tend to sting if they perceive a threat to the hive or are aggravated. That’s not to say that honey bees can’t be dangerous, especially to those who suffer allergic reactions to bee venom, but they are typically not as defensive as other social bee and wasp species.
The term “killer bee” likely stirs images of aggressive-looking bees with fierce, wasp-like features. In actuality, they look like a standard honey bee. Killer bees or Africanized bees are the same species as European honey bees, Apis mellifera, but a different subspecies.
Killer bees are a hybrid between the East African lowland honey bee (A. m. scutellata) and the European honey bee, originally bred with the intention of making a bee that produces more honey in tropical zones. Very similar in appearance killer bees are slightly smaller and lighter in color. Africanized bees are more defensive than European honey bees but also more productive pollinators and more resistant to disease.
The European bees were not performing well in the heat of the tropics in South America, and as a result, their honey production was low.
A more common name for the killer bees is Africanized honey bees, and the biologist that bred them did indeed manage to create a bee that produces more honey and was more suited to the hot climate. Brazilian scientist Warwick Kerr had several hives of the bees in south Brazil where he was studying them. Allegedly, he had placed queen excluders on the hives to prevent the queens from escaping and mating with the local bee population. These excluders were removed by a beekeeper that was visiting the site in 1957, and in doing so released 26 swarms.
Since then, the bees did precisely what Kerr had been trying to avoid. Mating with the local bees and forming new hives, Africanized honey bees have spread throughout the continent and into North America. They’re considered an invasive species, and have swarms as far north as California and Arizona.
So why are they called killer bees?
Africanized honey bees are known to be significantly more defensive than their European cousins. When provoked or feeling threatened, the bees will release an attack pheromone. Other honey bee species do as well, but killers bees seem to react more strongly to it. It supposedly smells like bananas, and once triggered the bees will swarm to defend the hive, and their victim is likely to receive as many as ten times more stings than they would from a European honey bee colony. They will also chase their alleged attackers for almost half a kilometre.
Their aggressiveness stems from the East African lowland honey bee. African bees have evolved to be more defensive since their hives are often destroyed by creatures such as honey badgers and humans. European honey bees have had centuries of breeding for more gentle strains, and the hives are maintained by humans to continue honey production. The crossbreeding kept in the defensive behaviour, and Africanized drones are more assertive in mating than the European drones. As well, they have been observed to enter a European honey bee hive, kill the queen, and replace her with a queen of their own. This has caused the killer bees to spread more quickly throughout South America; the primary honey bee species in Brazil is now the Africanized honey bee.
Africanized bees reportedly kill one or two people every year through their stings, but the term “killer bee” creates a problematic image. The bees do not actively pursue people, but rather are far more defensive of their nests. As well, their venom is no more potent than that of the European honey bee; the danger is in the number of stings that a person may receive. Their stingers are barbed, and the worker will die from stinging. Media portrayals have been little help to the situation, conjuring fear-inducing imagery of random attacks by furious swarms, rather than portraying reasonable caution.
Physical appearances make it difficult to differentiate Africanized bees from European bees. The hybrid bees are slightly smaller, and it’s suspected that they carry less venom as a result. The behavioural differences are less subtle, however. Killer bees are far more likely to swarm and abandon their hive when facing food shortages or overcrowding, but live in high densities. The greater numbers of larvae being produced means that the workers have to bring in more pollen, making them more efficient gatherers. In the European honey bee hive, the workers start their adult lives as nurse bees, feeding the larvae and cleaning hatched cells for the queen to lay an egg in again. It is not until they’re older that they will leave the hive to begin work as foragers. Killer bees become foragers at a younger age, likely to compensate for their high numbers.
Africanized bees also tend to live in ground nests and have a larger number of guard bees, though this may be in part be due to the fact that there are more bees in general in the hive.
The potential benefits
Despite the defensive nature of these bees, they have been noted to be superior at combating pests and diseases that other honey bees face, including varroa mites and chalkbrood. They also spend more time outside the hive, leaving earlier and returning later than the European honey bees. The potential for increased honey production and higher pollination rates make the Africanized honey bee a possible advantage.
With the way Africanized honey bees have spread and taken over, officials have been searching for ways to grapple with the defensive bees while maintaining the increased honey production. Breeders have been attempting to cross bees with the desired traits, and breed out the undesired aggressiveness. It has been speculated that attacks have been fewer since the accidental release of the killer bees in Brazil, but some argue that this may have less to do with genetics and instead is a result of better protective equipment and less damaging hive management, allowing beekeepers to navigate through the hive without triggering an aggressive response. Keeping apiaries away from livestock and dense human population areas has also provided potential improvements.
While honey production seems to be higher in tropical climates, the Africanized honey bees struggle with colder temperatures. The onset of warming global temperatures is a viable threat for the invasive species to continue moving north, but as of yet swarms have still kept to mostly tropical and desert areas. Despite only a couple deaths per year, the aggressive hive response can cause great injury, and is certainly an extremely painful experience.