Who would have guessed that our own backyards might be a battlefield for bees?

And that these deadly skirmishes involve aerial battles lasting days, with hundreds of fatalities from both attacking and defending sides, ousting the helpless from the hive and culminating in the eventual overthrow of the resident queen and installing their own in her place.

A cluster of dead native bees on the ground in a Brisbane backyard was enough to convince a group of scientists to dig deeper into this unusual behaviour of the Australian native bee species, Tetragonula carbonaria.

Their further investigations led to a surprising discovery, that the study colony was not only being attacked by its own species but also by a closely related species, T. hockingsi.

A fight to the death

Prior to this study, only the one species of bee, T. carbonaria was known to engage in battles between neighbouring colonies involving mass fatalities but this study provides the first evidence of fatal fighting between different species.

Fighting to the death or ‘fatal fighting’ is relatively rare in nature. Evolutionary biologists propose that this is because species have evolved different ways to assess strength and fighting ability that doesn’t involve the loss of the individual.

In species where fighting does escalate to death, scientific theory predicts the risk of death is outweighed by the benefits being obtained, such as fighting for scarce food resources, mates or nest sites.

Fatal fighting has been well studied in ants with beneficial outcomes including slave-making, raiding of nest supplies and gaining access to new food sites.

In the case of the T. carbonaria, the researchers hypothesised that the fighting swarms were most likely attempts at taking over neighbouring hives.

To test their hypothesis, they made regular observations on the ‘study’ hive in the backyard and collected the dead bees after fights for analysis. Using modern molecular techniques they were able to track which group of bees were attacking and which were defending. It was this analysis that lead to the surprising discovery that the attacking bees were in fact a separate species.

Following a succession of attacks by the same T. hockingsi colony over a four-month period, the defending T. carbonaria colony was defeated and the hive usurped, with the winning colony installing a new queen.

Hijacking Hives

To ensure that what had occurred at the study hive was not a one-off event, our researchers monitored the colonies of over 260 commercial T. carbonaria hives over a five-year period, recording any changes in species through changes in hive architecture (see note).

They found evidence of 46 interspecies hive changes (via the change in hive architecture) during the five year period, which were most likely to be usurpation events.

There is still much to be learnt about these small creatures, such as what instigates the attacks how and when the invading queen enters the nest, and whether the young in the usurped hive are spared and reared as slaves, or killed outright.

In the case of our native bees, it is thought that the capture of a fully provisioned nest (including ‘propolis’, pollen and honey stores) is a sufficiently large benefit that it outweighs the loss of so many lives.

Let’s ‘bee’ clear, we still need further research

The researchers are quick to point out that this is an excellent example of how little we actually know about small stingless bees, which can be an excellent and resilient alternative pollinators to declining honey bee populations.

NOTE: T. carbonaria has a brood chamber, in which cells are even and connected by their walls to adjacent cells at the same height, whereas T. hockingsi brood chamber takes on a less organised appearance, being an irregular lattice comprised of clumps of around ten cells connected by vertical pillars.

Find out more about our work leading the Global Initiative for Honey bee Health and the research we are conducting with bees.