These bees can't sting. They still go to war.
There are more than 500 species of stingless bees, living in warm places around the world. They make honey, raise their young in wax pots, and live in colonies with a queen, a lot like honeybees. But a nest full of honey is a target. And some stingless bees have found that it's easier to take another colony's food, or its whole home, than to build their own.
Robber bees: the bees that never visit a flower
In Central and South America, the robber bee Lestrimelitta limao has given up foraging completely. It has never been seen collecting food from flowers. It doesn't even have the pollen baskets on its back legs that other bees use to carry pollen home. Instead, it gets everything it needs by raiding other stingless bee nests and stealing their honey, pollen, wax and brood food.
The robbers have a chemical weapon. During a raid, they release citral, a lemon-scented chemical that throws the defending colony's defences into chaos. Many victims retreat inside their nest instead of fighting. Raids can kill adults and young and drain a colony's food stores, and some colonies never recover.
But not every species falls for it. Researchers noticed that bees that aren't thrown off by citral are rarely raided at all. The weapon only works on colonies that panic.
The first bee soldiers
One of the robber bee's favourite targets is the Jataí bee, Tetragonisca angustula, one of the most commonly kept stingless bees in Brazil. And it fought back by building something no bee was known to have: an army of soldiers.
Built for fighting
In 2012, Christoph Grüter, Cristiano Menezes and their colleagues showed that Jataí guards aren't just ordinary workers on guard duty. They're physically different. Guards are about 30% heavier than foragers, with wider legs, while foragers have bigger heads. In fights against robber bees, bigger guards did better.
Soldiers are expensive to raise, so the colony makes only a few. Only about 1 to 2% of new workers become guards. Some hover in the air near the nest entrance, and others stand on the wax entrance tube.
Calling in reinforcements
The guards can smell the enemy coming. When robbers attack, Jataí guards recognize the robbers' citral and other chemicals in their scent. The colony responds by sending hundreds of extra hovering guards into the air.
Robbers create armies
In 2017, Grüter's team looked at 28 species of stingless bees in Brazil and found special guard castes in ten of them. Those soldiers evolved again and again over the last 25 million years, around the same time robber bees appeared. In other words, the threat of being robbed is what pushed these bees to build armies.
Siege warfare in Australia
In Australia, stingless bees go further. They don't just steal food. They take over whole hives.
Around Brisbane, people had long seen huge swarms of sugarbag bees, Tetragonula carbonaria, fighting in the air, but nobody knew what the fights were for. Paul Cunningham, James Hereward and their colleagues used genetics to find out.
A four-month war
They followed one war in detail, starting in July 2008. The attackers turned out to be a different species, Tetragonula hockingsi, which had only recently spread into the area from further north.
- Battle one lasted three days, with about 50 pairs of bees fighting each day.
- Battle two lasted over two weeks. The attackers reached the front door and dragged some of the defenders' young out of the nest, but the defenders held on.
- Battle three raged for six days, with more than a thousand workers involved.
The bees fight jaw to jaw. Attackers lock onto defenders with their mandibles in a death grip, and neither bee survives. The ground below the hive was covered in a carpet of dead and dying bees. The researchers said it came down to a numbers game.
A new queen on the throne
After the third battle, the hive went quiet for months. When the researchers opened it and checked the new brood's genes, they found a new queen. She was the daughter of the attacking colony's queen. The attackers hadn't just raided the hive. They'd conquered it and installed their own ruler.
And this wasn't a one-off. Over five years, the team tracked more than 260 hives and found 46 likely takeovers.
Why stingless bees fight
A stingless bee nest is a store of honey, pollen and wax, built up over years of work. For a robber bee, raiding is cheaper than foraging. For a Tetragonula colony, taking over a hive is cheaper than building one. And for every colony that gets raided, the only real answer is to spend more on defence.
None of these bees have a sting. They've still worked out raids, chemical warfare, standing armies and regime change.
For more insect wars, read about the Argentine ant world war.
Further reading
- Blum, M. S., Crewe, R. M., Kerr, W. E., Keith, L. H., Garrison, A. W. & Walker, M. M. (1970). Citral in stingless bees: isolation and functions in trail-laying and robbing. Journal of Insect Physiology.
- Wittmann, D. et al. Robber bees (Lestrimelitta limao) and their host chemical and visual cues in nest defense by Trigona (Tetragonisca) angustula. Journal of Chemical Ecology.
- Grüter, C., Menezes, C., Imperatriz-Fonseca, V. L. & Ratnieks, F. L. W. (2012). A morphologically specialized soldier caste improves colony defense in a neotropical eusocial bee. PNAS.
- Grüter, C. et al. (2017). Repeated evolution of soldier sub-castes suggests parasitism drives social complexity in stingless bees. Nature Communications.
- Cunningham, J. P. et al. (2014). Bees at war: interspecific battles and nest usurpation in stingless bees. The American Naturalist.
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