Bees rolling balls around hailed as first evidence of insect play

In 2017, scientists in the UK carried out research suggesting that the small brain of the bumblebee may be more sophisticated than we realize, demonstrating how they could be trained to roll balls into a hole to score a sugary reward. The team has now delved deeper into the realm of entomological cognition with a new study demonstrating how the insects play with balls even when there’s no reward involved, constituting what they say is first-of-a-kind evidence of play behavior in insects.

In their earlier experiments where the bees were taught to score goals with wooden balls for treats, the scientists from Queen Mary University of London noticed something unexpected. Some of the bees were voluntarily rolling the balls around outside the experiments without any incentive. That they were doing so of their own volition suggested to the researchers that perhaps they were enjoying themselves, in the same way a dog might play with a fluffy toy or a kitten might tear apart a ball of yarn.

The team’s latest round of experiments were designed to test this idea, with groups of bumblebees placed in an arena where they had clear access to a feeding chamber and access to an area with wooden balls. And the balls started rolling, with individual bees engaging with them between one and 117 times, indicating that they were getting some sort of reward from the behavior.

Another round of experiments saw the bees given access to a pair of colored chambers, with one containing balls and another one completely empty. The balls were then removed, but the bees gravitated toward the previous play arena, showing a preference for the chamber where they had spent time with the wooden balls. Younger bees were found to roll the balls more than older bees, and males bees were found to roll them for longer periods than the female ones.

But satisfying the criteria for play behavior wasn’t as simple as removing the sugary reward, as there are other reasons the bees may be engaging the balls. The team used a framework laid out by evolutionary biologist Gordon Burghardt in his 2005 book The Genesis of Animal Play, based on the idea that play behavior can’t have a functional basis or result in an obvious or immediate outcome.

This means it should not be done to obtain food, mates or shelter. It should also be voluntary, spontaneous and rewarding in itself, and the motor actions must be different from those used for the purposes of the above. The behavior must be repeated and not one-off encounters, and it shouldn’t be undertaken in response to stress, like pacing or rocking seen in zoo animals in enclosures.

In their experiments, the authors saw no evidence of the bees extending their noses or biting the balls, like they might do when encountering nectar or pollen. The balls were placed well outside their nest area and the bees had clear access to food, to rule out the possibility that they were attempting to declutter their nests like they might do with dead adults or larvae. There was no evidence of stressful states or of mating-like behavior when encountering the balls, and the actions differed from the type of object manipulation seen in flower handling and from stinging when bees are in an agitated state. The authors write that the motor patterns involved “were structurally different from more adaptive activities in bumble bees' normal repertoire.”

All told, the scientists report that the ball-rolling fulfills the behavioral criteria for play in a similar way to that documented in other animal species, and believe the results constitute the first evidence of object play behavior in an insect. Burghardt holds a similar view, telling Science, “I think this is a great paper.”

As for why the bees might be engaging in play-like behavior is another question. Play behavior is believed to contribute to the development of cognition and motor abilities, such as foraging skills, for example. While the evidence suggests the bees found the ball-rolling rewarding, the scientists say further work is needed to understand the evolutionary advantages of it, and the role it might play in brain development.

“It is certainly mind-blowing, at times amusing, to watch bumble bees show something like play,” said study first-author, Samadi Galpayage. “They approach and manipulate these ‘toys’ again and again. It goes to show, once more, that despite their little size and tiny brains, they are more than small robotic beings. They may actually experience some kind of positive emotional states, even if rudimentary, like other larger fluffy, or not so fluffy, animals do. This sort of finding has implications to our understanding of sentience and welfare of insects and will, hopefully, encourage us to respect and protect life on Earth ever more.”

The research was published in the journal Animal Behavior, and you can see the bees in action in the short video below.

Source: Queen Mary University of London