Bumblebees Roll Little Wooden Balls Around, Apparently Just for Fun

A round, fuzzy bumblebee walks out of her nest and along a short path towards a dish of sugar water. Halfway there she stops, turns off to one side and takes hold of a small wooden ball with her legs. The ball tips, and bee and ball go rolling across the floor together. She lets go, walks over to another ball and does it again. The sugar water is still waiting. She does not seem to be in any hurry.

The question

Do insects play? For a long time the question hardly seemed worth asking. Play was for puppies, kittens and children. Then, in October 2022, researchers at Queen Mary University of London, working with colleagues at the University of Oulu in Finland, published a study in the journal Animal Behaviour with a plain title: Do bumble bees play? Their answer was yes, and the university described it as the first time that playing with objects had been shown in an insect.

How the test worked

The team watched 45 bumblebees in a small arena. Each bee could walk straight along a clear path to its food, or step off the path into areas with wooden balls. Nobody trained the bees, and touching a ball earned no food at all. They went anyway, again and again. Over the experiment, individual bees rolled balls between 1 and 117 times. Younger bees rolled more balls than older ones, and males kept a ball going for longer than females, a pattern the researchers compare to the play of young mammals and birds.

• 45 bumblebees in the first experiment
• 1 to 117 times a single bee rolled a ball
• 42 more bees in the second experiment, with coloured chambers

A second experiment asked whether the rolling was pleasant in itself. Another 42 bees were let into two chambers of different colours. One always held balls that could be rolled, and the other held none. Later the balls were taken away and the bees were offered the two colours again. They preferred the colour that had gone with the balls, rather like a child who stays fond of the room where the toys used to be.

What people often get wrong

The first mistake is to assume the bees were taught a trick. The same laboratory had earlier trained bumblebees to roll a ball to a target for a sugary reward, and it is easy to mix the two studies up. This time there was no training. The idea came from that earlier work, in fact, when researchers noticed bees rolling balls outside the experiment, for nothing. The second mistake is the old picture of insects as tiny machines that only ever do what is useful. The third runs the other way: the study does not show that a bee feels joy as we do. Its first author put it carefully, saying the bees may experience some kind of positive emotional state, even if a rudimentary one.

How we know it was play

Biologists do not call something play just because it looks sweet. They use a checklist, and according to the paper the ball rolling met five points on it: it did nothing for immediate survival, it seemed to be rewarding in itself, it looked different from the bees' useful behaviours, it was repeated without being the same stiff movement every time, and it happened when the bees were relaxed. The team also ruled out the dull explanations, that the bees were searching the balls for food, clearing clutter out of the way or looking for a mate. Take away every sensible reason and what is left is the least sensible and most charming one: a bee, a ball and nothing better to do.