Playtime isn’t just for children. Lab-kept bumble bees roll small wooden balls around for no apparent purpose other than fun, a new study reveals. The finding supports evidence that bees experience pleasure, researchers say, highlighting the importance of protecting them in the wild and treating them well when they’re kept in hives.
“It is super cool,” says Elizabeth Tibbetts, an evolutionary biologist at the University of Michigan, Ann Arbor, who was not involved. “We usually think about insects as being so different that they lack sophisticated behaviors.” But not everyone is convinced the behavior is in fact play.
In animals, play helps the brain develop: Fox cubs pretend-fight to learn social skills, for example, and dolphins and whales jump and spin even without predators around. A study in 2006 described behavior in young wasps (Polistes dominula) that looked like play fighting, but whether other insects play hasn’t received much research attention.
Lars Chittka, a behavioral ecologist at Queen Mary University of London (QMUL) and author of the recent book The Mind of a Bee, and colleagues stumbled upon the new evidence by accident. The team was studying how bumble bees (Bombus terrestris) learn complex behaviors from their comrades by training the insects to move wooden balls to specific locations. (If a bee moved a ball to the right place, it got a sugary treat.) The researchers noticed that some bees moved the balls even when no reward was offered. “They just seem to like going back to them and fiddling with them and rolling all over the place,” Chittka says.
Samadi Galpayage, then a master’s student at QMUL, was fascinated by the bees’ many behaviors. “I couldn’t help falling in love with them,” she says. “I stayed on to do a Ph.D. to learn more.”
Galpayage set up what was essentially a single-story apartment for the bees. At one end was the nest, which had a single entryway to a recreation center. The far end of the rec room connected to a cafeteria with an all-you-can-eat supply of pollen and sugar water.
The recreation center was where the experiment took place. This room had two play areas on either side, each with wooden balls that were slightly bigger than a bee. The balls couldn’t roll onto the path, so the bees had to literally go out of their way to play with them.
In the first experiment, Galpayage and colleagues immobilized the balls on one side. To get to the buffet, the bees had to walk through the recreation room—and past the ball areas—and they clearly preferred the side with the balls that rolled, entering it 50% more times, on average. That suggests the bees like the movement, not just round objects.
Measuring how many times each bee rolled a ball (see video, above), the team found that some only did so once or twice, but others rolled them up to 44 times in a day. The repetition implies they are enjoying the activity, Galpayage says.
To confirm that rolling these balls is indeed the bees’ knees, Galpayage set up another experiment with a new nest of bumble bees. Like the previous design, bees leaving the nest passed through a chamber to get to the food. For the first 20 minutes, the chamber was colored yellow and contained the wooden balls. Then, Galpayage swapped in a blue chamber without balls. She alternated the colored chambers six times, training the bees to associate the color yellow with the presence of balls. Finally, Galpayage gave the bees a choice between entering a yellow or blue passageway without any balls in sight.
The bees favored yellow—aboutone-third more chose it—presumably because they associated it with the pleasurable sport of ball-rolling, the researchers report this week in Animal Behaviour. When the team reversed the colors and repeated the experiment, they got similar results. “I think it provides really good evidence that [rolling balls] is rewarding,” Tibbetts says.
The experiment also revealed that young bees were more likely to roll a ball than were older bees. This reflects how play changes with age in birds and mammals; young animals are more likely to play. Researchers think their developing brains might benefit from the experience, for example by strengthening neuronal connections involved in muscle coordination. The bee brain is also better able to form new connections early in life, before workers first leave the nest to begin foraging.
Galpayage is now investigating whether ball rolling improves the ability of adult bees to efficiently harvest nectar from flowers.
Gordon Burghardt, an expert in animal behavior at the University of Tennessee, Knoxville, says the careful design of the experiments has convinced him the bees are indeed engaging in play. “I think this is a great paper.”
But Sergio Pellis, who studies animal behavior at the University of Lethbridge, isn’t fully sold. Even though the experimenters gave the bees a clear path to a reward, he wonders whether the balls still might be triggering the housekeeping behavior that the bees use to remove dead bees and other debris from their nests. To make a stronger case that bees can experience pleasure, he says, it would help to have more examples of play.
Even if the bees are indeed playing, it’s unclear whether they would do so in the wild. It’s possible that bees in the lab have more opportunities for play because they are protected from predators and don’t need to gather food, Chittka says. “Competition in the wild is tough and might not provide bees with the luxury to set aside time to manipulate objects just for fun.”
Because play implies a capacity to experience emotions, the researchers say, documenting it in insects could have ethical implications. Insects are increasingly being reared for animal feed, and there are no regulations governing their welfare, Galpayage notes. Honey bees are also known to become stressed and more vulnerable to disease and colony collapse when industrialized beekeepers transport them long distances on trucks to orchards and vast fields without diverse flowers nearby, Chittka says. The researchers hope their findings might also motivate greater empathy for—and protection of—wild insects.