Bumblebees rolling wooden balls may be first evidence of insect play

Bumblebees play, possibly just for the fun of it. The insects repeatedly chose to roll wooden balls in an experiment despite having no clear reward for doing so. The discovery may be the first documented evidence of insects playing.

Samadi Galpayage at Queen Mary University of London and her team were inspired to investigate if bees play after finding that the insects could be trained to balls into tiny soccer goals for a food reward in 2017.

In a new study, the team placed 45 buff-tailed bumblebees (Bombus terrestris audax) of different sexes and ages in an arena with a single entrance. There was a clear aisle from the entrance to pollen and sugar water in the back of the chamber, but the insects had to pass between two adjacent rooms with 18 colourful wooden balls to get there. One room had free-moving balls, while the other had balls that were glued down.

Over 18 3-hour sessions, the bees opted to enter the zone with free-moving balls 50 per cent more often than the zone with stationary balls. Each bee rolled balls between one and 117 times throughout the study despite having no obvious incentive to do so.

“When you look at the videos of the bees on the balls, if you saw that in a dog, or a monkey, or even a bird, we’d have no problem calling it play,” says Gordon Burghardt at the University of Tennessee, Knoxville, who was not involved in the work.

Not all bees had the same knack for playfulness. Younger bees rolled more balls than older bees, and males rolled balls for longer than females of the same age. Just as kittens and puppies pounce and wrestle to build hunting skills, the mental and physical exercise of play may be especially beneficial during bumblebees’ youth, says Galpayage.

Because ball-rolling appears spontaneous and voluntary and doesn’t have immediate or long-term benefits for the insects, they could be doing it to have a good time, says Galpayage. “With humans, we can ask, ‘Are you having fun?’,” she says. “Whereas with animals, it’s always difficult to assess that.”