The killer bee: the case that shook up America

In the ‘60s, American media picked up a case that shook up countries all over the world: hybridization of two types of honeybee gave rise to an aggressive, unstoppable and lethal new organism. The killer bee had arrived.

This little insect appeared on the front cover of numerous famous magazines and newspapers during a long time and it even assumed the main role in some terror films (such as “The Swarm”, 1978). However, when did fiction surpass reality? What’s true in this story? Keep reading to get the answers.

The origin of killer bees

The most famous honeybees belong to the species Apis mellifera, which is widely spread all over the world. All its subspecies are native to Europe, Africa and Asia, although some of them (specially the European ones) have been imported to different countries worldwide due to their value for crop pollination and honey production.

You can read the post ‘Family life of bees and beekeeping‘ to know more about this topic.

The breeding of honeybees (beekeeping or apiculture) is a widespread practice all over the world. In America, European honeybees were imported for this purpose. Author: Emma Jane Hogbin Westby, CC on Flickr.

The origin of killer bees underlies on the subspecies A. mellifera scutellata or African honeybee, native to Sub-Saharan Africa and southeast of Africa. Unlike European honeybees, these are very aggressive. In America, these bees hybridized with imported European or Western honeybees, giving rise to hybrid bees known as Africanised bees. These hybrids, along with native African honeybees and the descendants they gave birth in America, were colloquially named as killer bees.

Native range of distribution of the African honeybee. Source: UF/IFAS, University of Florida. Original illustration property of Jane Medley, University of Florida.

How and why did they spread over America? 

In the ’50, the importation of European honeybees to America was a frequent practise. However, while beekeeping had good results in the USA, it didn’t seem to work in South America because honeybees from Europe didn’t adapted well to tropical climate. Thus, in 1956, the Brazilian scientist Warwick Kerr suggested to import African honeybees to Brazil instead of the European ones in an effort to increase honey production. Then, the unique main problem he needed to solve was the aggressive nature of this subspecies. The main objective of Dr. Kerr was to obtain a docile variety of bees that was also productive in tropical climates by artificial selection and cross-breeding of the African honey bee (A. m. scutellata) with various European honeybees.

The project would had been a success if it weren’t for the fact that some swarms accidentally escaped quarantine. The experimental bees rapidly formed new colonies and began to hybridize with both wild and domestic European honeybees, giving rise to the Africanised honeybees which were more aggressive and less productive than Dr. Kerr expected.

These bees are currently located in almost all over the American continent. In the USA, they didn’t spread further north due to their tropical origins, so their range of distribution in North America is limited to the southern states of the USA.

The spread of the killer bee over America was fast, even reaching the southern states of the USA in a few years since they escaped. Source of the original illustration: Harvard University Press (86).

Analysing the killer bee

Morphology

At the beginning, beekeepers faced the difficult to differentiate the African honeybees from the European ones, because they look quite similar at first glance. However, exhaustive studies allowed to confirm the existence of, at least, two differences between them: both African and Africanised honeybees are slightly smaller (about 10%) and darker than the European ones. Bad news is that it’s still necessary to use morphometric analysis to differentiate them properly, especially when African genes are more diluted.

To the left, Apis mellifera scutellata or African honeybee; to the right, Apis mellifera mellifera or one of the European subspecies of honeybees. Author: Scott Bauer, USDA Agricultural Research Service, United States. Public domain.

Behaviour

African honeybees show some behavioural traits that make them potentially more dangerous than their European relatives:

1. They are more aggressive. It’s suggested that being exposed to different environmental pressures in their native habitats could be the main cause of the difference of aggressiveness between these honeybee subspecies: traditionally in Europe, beekeepers have selected less aggressive and manageable varieties, while in Africa it’s more usual to collect wild honeycombs (a practice colloquially known as ‘honey hunting’). Both ‘honey hunting’ and a major presence of natural enemies could have been lead to the selection of African varieties’ heightened defensiveness compared to that of European subspecies.

2. They accomplish massive attacks. Unlike European honeybees, which attack in groups of 10-20 individuals, African honeybees can do it in groups of 100-1000 individuals. There exist evidences of the emission of pheromones that would incite other bees to massively join the attack. Moreover, the defended area around the nest is greater and the level of stimulus needed to trigger an attack is lower than in the European honeybees.

Massive attacks accomplished by African and Africanised bees are infrequent, but stunning. In the image above, the farmer Lamar LaCaze was attacked by a swarm of 70.000 Africanised honeybees that had made their home in an old water heater (Source: Inside Edition). In the image below, the case of the climber Robert Mackley, who was attacked during about 3 hours while performing an ascension in Arizona; he was stung an estimated 1500 times (Source: Phoenix New Times; author of the picture:: Robert Mackley).

3. They swarm frequently. Honeybee colonies usually swarm 1 to 3 times a year (i.e. when the colony gets too large and resources are abundant, a new queen is reared and the hive splits), while African honeybee hives could split up to 10 times a year, even more if they feel threatened.

Swarm of African honeybees. Author: Michael K. O’Malley, University of Florida.

4. Selection of nesting site. Because African honey bees swarm more often, fewer individuals are involved in each swarm, so they do not require a large cavity to build a nest. They are also less selective than their European relatives, so they can be found inside pipes, trash cans, building cracks, holes in the ground, etc.

A colony of African honeybees inside a bucket. Author: Michael K. O’Malley, University of Florida.

Nest of Africanized honeybees in a building ceiling. Author: Ktr101, CC.

5. Nest usurpation (or colony takeover). This is probably the most curious behavioural trait of African honeybees. First of all, a small African swarm containing a queen lands on a European colony. As time passes, the worker bees in the African swarm begin to exchange food and pheromones with the European workers from the colony. This gradually ensures the adoption of the African bees into the European colony. Somewhere during this process, the European queen disappears (probably killed by the African bees) and the African queen is introduced into the colony. By this process, European bees are eventually substituted by African bees and their hybrid descendants.

Biology

Even though reproductive biology and development are very similar among honeybee races, African honeybees show some biological traits that lend them adaptive advantages with respect the European ones:

1. Greater production of drones (male bees) by parthenogenesis. African colonies produce proportionally more male bees than European honeybees, which gather during the nuptial flight forming cloud of hundreds of individuals. So, the probability that a European queen mates with an African drone increases, and thus the probability to perpetuate African genes.

2. Fast development. African colonies grow and spread faster than the European ones.

3. Greater resistance to pathogens and parasites. For example, to Varroa destructor, to the small hive beetle Aethina tumida or even to bacteria of the genus Paenabacilis, which have finished with a lot of European honeybee populations in America.

Varroa destructor on a bee nymph. Author: Gilles San Martin, CC.

The way all these traits express on hybrid bees varies depending on the proportion of African and European genes they present, which depends at the same time on the distance to the original spreading focus. So, the hybrid bees from the USA tend to be genetically closer to European honeybees and thus are less aggressive than the Africanised honeybees from other parts of America.

Are they a public health concern?

The number of stings received by their victims (causing anaphylactic reactions even in non-allergic people), the aggressiveness of their attacks, their versatility to select a nesting site (favouring their presence in urban areas) and their sensibility against any vibration or noise, are reasons enough to consider both African and Africanised honeybees a public health concern.

However, the most stunning cases of massive attacks are not as frequent as we could think. So, the real concern falls to risk groups (such as children, elderly, sick or disabled people) and to domestic animals, which would have more difficult to scape an attack.

Despite the potential risk they pose, the situation is currently well managed because a great number of exhaustive studies have allowed to carry out different measures to control their populations (and even to take advantage of them). For many years, beekeepers have been breeding African and Africanised bees to produce honey and pollinize crops in Centre and South America, becoming one of the most important honey producers worldwide. To that effect, they apply special management measures, such as letting only one colony to develop inside the hive.

Installing alert signs minimizes the risk that people come in contact with colonies of bees. Along with the premature detection of individuals and the elimination of potential nesting sites, this action is a part of the set of preventive measures to prevent the progression of their populations and the interaction of people with these organisms. Source of the picture: ALTHEA PETERSON/Tulsa World.

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Despite ‘killer bees’ could be dangerous depending on the situation, they must not be considered a great concern due to the great amount of information there exists about their populations and also about measures to control them. However, this case serves as an example of how the impact of humans on ecosystems and the introduction of foreign species can play a dirty trick on native habitats…

REFERENCES

• Calderón, R. A., Van Veen, J. W., Sommeijer, M. J., & Sanchez, L. A. (2010). Reproductive biology of Varroa destructor in Africanized honey bees (Apis mellifera). Experimental and Applied Acarology, 50(4): 281-297.
• Ellis J., Ellis A. (2012). Apis mellifera scutellata Lepeletier (Insecta: Hymenoptera: Apidae). Entomology and Nematology Department, University of Florida, USA [en linia].
• Evans, H. E. (1985). “Killer” Bees, The Pleasures of Entomology: Portraits of Insects and the People Who Study Them. Smithsonian Institution, Washington D.C. Pp 83-91.
• Ferreira Jr, R. S., Almeida, R. A. M. D. B., Barraviera, S. R. C. S., & Barraviera, B. (2012). Historical perspective and human consequences of Africanized bee stings in the Americas. Journal of Toxicology and Environmental Health, Part B, 15(2): 97-108.
• França, F. O. S., Benvenuti, L. A., Fan, H. W., Dos Santos, D. R., Hain, S. H., Picchi-Martins, F. R., Cardoso J. L., Kamiguti A. S., Theakston, R. D. & Warrell, D. A. (1994). Severe and fatal mass attacks by ‘killer’bees (Africanized honey bees—Apis mellifera scutellata) in Brazil: clinicopathological studies with measurement of serum venom concentrations. QJM, 87(5): 269-282.
• Neumann, P., & Härtel, S. (2004). Removal of small hive beetle (Aethina tumida) eggs and larvae by African honeybee colonies (Apis mellifera scutellata). Apidologie, 35(1): 31-36.
• O’Malley, M.K., Ellis, J. D., Zettel Nalen, C. M. & Herrera P. (2013). Differences Between European and African Honey Bees. EDIS.
• Winston, ML. (1992). Killer Bees: The Africanized honey bee in the Americas. Harvard University Press, Cambridge, Massachutes, USA. 176 pp.

Main photo property of Gustavo Mazzarollo (c)/Alamy Stock Photo.