Play is usually identified as a uniquely mammalian trait. We recognize it in our pets, in non-human primates, and even wild animals. But we don’t often recognize it in non-mammalian animals; especially insects. Many people dismiss insects as being base creatures with base instincts: eat, sleep, mate, don’t get eaten. But recently, researchers have provided evidence that insects do in fact engage in play; suggesting that some form of insect sentience is likelier than we may have realized.

Recognizing play behavior isn’t just a question of whether or not it looks like someone (or something) is having fun. Researchers have outlined a very specific framework for recognizing play behavior in animals. First, the behavior cannot be motivated by reward, e.g. food or access to mates. Second, the behavior should be voluntary, spontaneous, and a reward in and of itself. Third, the behavior should exhibit different characteristics than functional actions, i.e. it doesn’t resemble functional behavior like foraging. Fourth, the action is repeated, but not “stereotyped”; some animals in stressful captive conditions will exhibit rocking or pacing behavior. This repetitive motion is recognized as a stress response, not play. Finally, play behavior is inherently pleasurable, and animals will only engage in play when they are relaxed and in a stress-free environment.

So what could this possibly look like for insects? In a study published last October in Animal Behavior, researchers were able to identify play behavior in bumblebees, and like so much science, the study came about by accident. Bees are incredibly smart insects, and several studies have come forth in recent years demonstrating their abilities to be trained to perform specific actions. During a 2017 study where researchers were training bumble bees to roll small wooden balls for a food reward, they noticed the bees would occasionally roll the balls unprompted, and for no apparent benefit. This led to the question, are the bees engaging in play?

To test this hypothesis, researchers assembled a play arena for bumble bees. They connected the arena directly to the hive to avoid excessive handling, which could cause undue stress for the bees. During the trials, in which the bees were provided unobstructed access to unlimited food, researchers found that the bees would preferentially return to the section of the arena where they could roll wooden balls. Another section of the arena was devoted to wooden balls that were glued to the ground; once the bees realized they could not roll the balls, they abandoned that section of the arena and did not return.

Researchers also found that younger bees were more likely to roll balls for longer periods of time, a behavior analogous to mammalian play. Additionally, they noticed male bees rolled the wooden balls for longer durations than female bees (take that as you will).

In a follow-up experiment, the bees were split into two groups. One group would engage in ball-rolling in a blue chamber, the other would engage in ball-rolling in a yellow chamber. Researchers chose these colors because bees are easily able to distinguish between the two. When both groups were later offered a choice between the two colored chambers, the bees would more often than not choose the chamber they associated with ball-rolling. Like the first experiment, bees were provided with unlimited and unobstructed access to food, so they could forage as needed; but food was never provided directly by the researchers after observing ball-rolling behavior.

Ultimately, the researchers found that ball-rolling appeared to be an inherently rewarding experience for the bees, free from incentive. They found that the behavior fit the established play criteria and mimicked play behavior often observed in mammals. Play is an important behavioral tool for young mammals; it improves motor function and is crucial to the early development of the brain. Organisms are often classified by levels of sentience; mammals are considered “higher-ordered” than organisms like fish, amphibians or insects because their behavior is is so easy to recognize in ourselves. This study provides evidence that it’s not just mammals who benefit from this behavior; and perhaps we have more in common with our so-called “lower-ordered” organisms than we have been led to believe.