Animals & nature · 2022
Do bumble bees roll balls to play rather than to find food?
Yes—under experimental conditions, wooden-ball rolling by bumble bees of the species Bombus terrestris met behavioural criteria for play. The experiments ruled out food searching, clutter clearing and mating as explanations, and bees preferred the colour of a chamber where they had rolled balls over the other chamber’s colour. This supports the idea that rolling was rewarding, but does not establish that bees experience enjoyment as humans do.
Details
Researchers tested whether bumble bees’ interactions with wooden balls qualified as object play, a behaviour whose clearest examples have mostly come from mammals and birds. Rolling met five behavioural criteria: it had no immediate survival function, was rewarding in itself, differed in form from practical behaviour, was repeated without following a rigid pattern, and began under stress-free conditions.
A colour-preference experiment provided evidence that rolling itself was rewarding. Bees were trained to find freely movable balls in one of two differently coloured chambers. Afterwards, they preferred the colour associated with the chamber where they had rolled balls. The experimental design and behavioural observations also ruled out food searching, clutter clearing and mating as explanations for rolling.
Younger bees rolled more balls than older bees, while males rolled individual balls for longer than females. Together, the findings support interpreting this behaviour as play in this species under the tested conditions. They also support the possibility of positive emotional states in insects, but the behavioural evidence does not directly establish what the bees felt.
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