Why Do Bumblebees Suddenly Overthrow Their Queen And Murder Each Other?

Bumblebee colonies sometimes mysteriously collapse into violent disorder. Steven Ellingson/Shutterstock
Robin Andrews 07 Jan 2016, 22:34

When you think of the humble bumblebee, images of an orderly, organized, efficient bee colony are likely to come to mind. Although for the most part this picture of a perfect colony is accurate, there comes a time when the colony descends into a pandemonium of violence, deceit, and murder. A new study, published in the journal Royal Society Open Science, reveals for the first time why this happens: it’s all down to the changing chemistry of the beeswax.

During the “social phase” of a colony of Bombus terrestris, it is the epitome of efficiency. The queen initially becomes fertilized by a male; shortly afterwards, she begins laying her multitude of eggs. Then, she lets herself be pampered, protected and fed by her children, who are mostly worker bees.

The occasional male is produced, which may later mate with a virgin queen. The worker bees, who are always female, continuously forage for nectar and food, look after younger worker bees, and tend to the nest. They also keep an eye out for any potential external aggressors.

According to the lead author of the study, Anne-Marie Rottler-Hoermann, a researcher at the Institute of Evolutionary Ecology and Conservation Genomics in Ulm, Germany, this militaristic organization explains why bee colonies are so prosperous. It is this regimented division of labor, and the lack of any type of sexual conflict, that “can be considered the main reason for the great evolutionary and ecological success of social insects,” she said in a statement.

Eventually though, something rather dramatic happens: the bees suddenly turn on each other in a fit of bitter violence. During this “competition phase,” the bumblebees start to murder each other rather quickly, while also destroying the fertilized eggs made by the queen.

For the queen? Not so much. TTStudio/Shutterstock

During this massacre, the queen loses her grip on the colony. Her female worker bees begin to lay unfertilized eggs, producing only males with a single set of chromosomes; this causes the genetic variability of the colony to plummet. In the midst of all this aggression, the queen herself can sometimes be killed in an act of bee-based regicide.

For a long time scientists were unsure as to why this insurrection began, although they suspected it was to do with the rapid size increase of the colony, which can contain up to 150 worker bees in less than a year. However, this new team of researchers suspected that the changing chemistry of the beeswax may be to blame.

The bumblebees’ wax contains a combination of compounds (lipids) that are emitted by both the queen and her workers; the more bees present in the colony, the more significant the build-up of these lipids will be. By placing a variety of bees in specially designed nests with a range of beeswax types, and continuously tracking the wax chemistry, the researchers discovered something remarkable.

By constantly checking the lipid content, the bees determine at which point the colony becomes unstable. This occurs when there are perhaps too many worker bees, the queen becomes less fertile, or a fight to become the new virgin queen breaks out.

Whenever this end-game phase wax chemistry is detected, the violent uprising begins. Even when this wax is inserted into a separate colony operating harmoniously in the social phase, the bees begin to kill each other, despite a commanding, fertile queen being present.

It seems that even for bees, when you play the game of thrones, you win or you die.

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