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Bumble bees can "play" with objects for fun

We are all familiar with the engaging antics of young mammals and birds as they play. They undertake activities with no apparent immediate purpose, other than to bring enjoyment. But is it possible that insects may also have a sense of playfulness? 

In previous research on bumble bees, scientists found that they could train bees to roll small wooden balls along in exchange for a sugary reward, but they also observed that the same bees went out of their way to visit the balls and roll them around, even when there was no reward involved. This led the researchers to wonder whether these bees were actually engaging in play.

According to behaviorists, play can be defined according to five criteria. It is activity that has no immediate adaptive outcome, is voluntary and spontaneous, is different from usual functional behavior, is often repeated but not stereotyped, and is initiated when an animal is in a relaxed, unstressed state. With these criteria in mind, a research team led by Queen Mary University set out to test whether the bumble bee behavior of rolling balls around fulfilled the definition of play. 

Their initial experiment followed 45 novice bumble bees as they made their way from a nest to a feeding area where ‘nectar’ and pollen were available. On the way there, the bees could choose a direct path or could deviate into areas where either mobile or immobile wooden balls were available on the floor. The balls were all 15 mm in diameter and were either painted yellow or purple, or left the natural wood color. The experiment ran for 3 hours each day, over 18 days, and video recordings were made of all the bee movements.

The study, published in the journal Animal Behaviour, reported a total of 910 ball-rolling actions by the 45 bumble bees. Individual bees rolled balls between 1 and 44 times on an experimental day, and between 1 and 117 times across the whole duration of the experiment. In addition, individual ball-rolling actions lasted between 0.4 and 31 s, and for distances between 2 and 601 mm. Statistical analysis showed that, after a bee’s first ball-rolling experience, it was more likely to enter the area of mobile balls than the area of fixed balls. As no food reward was associated with visits to the balls, the researchers concluded that the bees were choosing to visit the balls for reasons not related to foraging or any other functional purpose. 

The study also found that younger bees (less than 7 days since emergence) rolled more balls than older bees, mirroring the more playful behavior of young humans and other juvenile mammals and birds. Furthermore, although male and female bees rolled comparable numbers of balls, male bees rolled them for longer time periods than their female counterparts. For female bees the ball-rolling behavior peaked at the age of 3 days while for males it peaked at the age of 5 days. 

In a subsequent experiment, the researchers first gave 42 bumble bees access to two chambers, each of a different color. One chamber always contained movable balls and the other had no objects inside it. Once the bees were accustomed to finding balls in a chamber of a particular color, they were tested and given a choice between the two chambers, this time though, neither one contained any balls. The bees showed a striking preference for the color of the chamber previously associated with the wooden balls. These results again suggest that bumble bees find ball rolling rewarding and seek to repeat the experience.

The set-up of the experiments removed any notion that the bees were moving the balls for any greater purpose other than play. Rolling balls did not contribute to survival strategies, such as gaining food, clearing clutter, or mating and was done under stress-free conditions. The researchers concluded that the seemingly functionless ball-rolling activity is analogous to object play in mammals, and fulfils all the criteria of play behavior. 

“It is certainly mind-blowing, at times amusing, to watch bumble bees show something like play. They approach and manipulate these ‘toys’ again and again,” said study first author Samadi Galpayage. “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 for our understanding of sentience and welfare of insects and will, hopefully, encourage us to respect and protect life on Earth ever more.”  

“This research provides a strong indication that insect minds are far more sophisticated than we might imagine. There are lots of animals that play just for the purposes of enjoyment, but most examples come from young mammals and birds,” said Professor Lars Chittka, author of the recent book The Mind of a Bee. “We are producing ever-increasing amounts of evidence backing up the need to do all we can to protect insects, that are a million miles from the mindless, unfeeling creatures they are traditionally believed to be.”

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By Alison Bosman, Staff Writer

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