For decades, scientists have known that insects are capable of complex tasks, such as counting and showing a sense of rhythm. However, determining whether they have feelings or subjective experiences has remained a major challenge. Because insects lack the flexible facial muscles of mammals, they cannot easily express their emotions.
Now, a team of researchers led by Andrew Barron at Macquarie University in Sydney, Australia, has found a creative way to study this mystery. By using high-resolution video cameras, they analyzed the tiny mouth movements of buff-tailed bumblebees (Bombus terrestris) during feeding experiments.
In the first experiment, the researchers offered the bees droplets of sweet sugar water, salty water, and bitter quinine. The video showed that after tasting the sweet liquid, the bees repeatedly stuck out their glossa, which is a hairy tongue they use to drink nectar. In contrast, after tasting the salty and bitter liquids, the bees wiped their mouths and shook their heads.
To determine if these actions were simple chemical reflexes or represented actual pleasure and displeasure, the researchers changed the bees' internal states. They exposed the bees to high temperatures of 40°C (104°F) to dehydrate them. When these thirsty bees were offered salty water, they repeatedly stuck out their tongues. According to Barron, this is similar to how a human might dislike the taste of an electrolyte drink normally, but find it delicious after a long, exhausting run. The bees' evaluation of the taste changed based on their physical needs, demonstrating a flexible response rather than a robotic program.
Finally, the team investigated the brain chemistry that regulates appetite and enjoyment. In mammals, dopamine controls the motivation to seek food (wanting), while endocannabinoids control the actual enjoyment of food (liking). When the researchers treated the bees with dopamine, their tongue movements did not change. However, when treated with endocannabinoids, the tongue movements increased. This is the first time scientists have successfully separated the feelings of "wanting" and "liking" in an insect.
While some experts, such as Ralph Adolphs from the California Institute of Technology, caution that bees likely experience "bee emotions" rather than human-like pleasure, others believe the study is a breakthrough. Jonathan Birch from the London School of Economics noted that the research is part of a "golden age" of studies using modern technology to reveal complex animal behaviors that humans have missed for centuries.