Play is usually identified as a uniquely mammalian trait. We recognize it in our pets, non-human primates, and wild animals. But we don’t often recognize it in non-mammalian animals, especially insects. Many people dismiss insects as base creatures with base instincts: eat, sleep, mate, and don’t get eaten. Recently, several studies have provided evidence that insects 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 relaxed and in a stress-free environment.
So, what could this possibly look like for insects? In 2022, researchers at the School of Biological and Behavioural Sciences at Queen Mary University of London identified play behavior in bumblebees, and like so much science, the study came about by accident. Bees are brilliant insects, and several studies have come forth in recent years demonstrating their abilities to learn and 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 puzzling behavior 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) and provided them with unobstructed access to food. During the trials, researchers found that they would preferentially return to the arena section 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, 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).
Another experiment from 2023 conducted by researchers at the University of Leipzig found evidence of play in fruit flies. Instead of ball rolling (imagine how small those balls would have to be), they offered the flies an entirely different but relatable experience: a ride on a carousel. This type of play is defined as “locomotor play,” and just like humans, not everyone is into it. Flies are well-known to have excellent spatial memory, and some individuals avoided the carousel (a spinning disk on the floor of the experiment enclosure) altogether. But others went back – again, and again, and again. “It’s clear that at least some of the flies are engaging in this locomotor behavior just for the hell of it,” says Sergio Pellis, a behavioral scientist at the University of Lethbridge.
Organisms are often classified hierarchically by levels of sentience. Mammals are considered “higher-ordered” than organisms like fish, amphibians, or insects because their behavior is so easy to recognize in ourselves. Ultimately, both studies show that their insect subjects engage in an inherently rewarding experience free from incentive. The behaviors fit the established play criteria and mimic play behavior recognized in mammals. Play is an essential behavioral tool for young mammals; it improves motor function and is crucial to the early development of the brain. These studies provide evidence that it’s not just mammals who benefit from this behavior; and perhaps we have more in common with so-called “lower-ordered” organisms than we have been led to believe.