New research proving bumblebees exhibit emotion-like behaviours – previously thought only to exist in mammalian species – has implications for how scientists understand the consciousness of insects.
The first-of-its-kind study, published today in Proceedings of the National Academy of Sciences , used slow-motion video that captured how bumblebees shake their heads and wipe their mouths if they don't like food – and "lick their lips" if they do.
Professor Andrew Barron from Macquarie University in Sydney, Australia, says the revelation changes our scientific understanding of the inner life of insects.
"Facial expressions are an important window into the internal states of animals. There's always been a tension between thinking of insects as animals or some sort of mini robots. This is another step towards showing there's an inner life to being a bee."
Led by researchers Fei Peng and Cwyn Solvi at Southern Medical University in Guangzhou, China, the study of 18 colonies of bumblebees (Bombus terrestris) found the insects could show observable "liking and disliking" behaviours, as opposed to "wanting" actions or feeding reflexes.
"Many people are comfortable saying that insects can sense, learn, and make decisions, but much less comfortable saying that they may evaluate things as pleasant or unpleasant. Our findings push on that intuition," says Professor Peng.
Key findings include:
The bumblebees displayed distinctly different orofacial behaviours after consuming sweet liquids versus bitter and salty liquids.
Post-consumption glossa ("tongue") protrusions – akin to "licking their lips" – occurred after eating sugar solutions.
Aversive head shaking and mouth wiping occurred after tasting salty and bitter liquids.
This emotion-like behaviour has never been observed outside of mammals.
"We don't yet understand what the bees truly experience, but we can observe emotion-like behaviours," says Professor Barron, a neuroethologist who studies the connections between animal behaviour and its underlying control by the nervous system.
"What's important is we've now got a practical read on their inner life that we can work with experimentally."
Professor Barron says the implications extend beyond bees to all insects.
"In terms of how the brain is organised, there's no major difference between a bee and a fly – this means there's more to consider in terms of how we might treat or react to insects. By human standards, the bee brain is tiny – weighing less than a milligram – and yet our evidence suggests the remarkable bee brain can support a form of bee inner life."
He says the work is an important step toward understanding how brain activity relates to subjective experience.
"We hope further studies will show how the bee's mental life arises from mechanisms in the brain so we can close the gap between the mental and the physical."
