When bumblebees taste something good, they reach out their glossa – or insect tongue – for a while afterwards, almost as if they are licking their lips. And when they don’t like something, the insects will shake their heads and wipe their mouths.
Scientists who captured the miniature facial expressions on slow-motion video say the behaviour is consistent with “liking” and “disliking” responses observed in mammals. Their results have been published in the journal Proceedings of the National Academy of Sciences.
In the study, a collaboration between Macquarie University and the Southern Medical University in China, researchers presented bumblebees with droplets of different solutions – 60% sugar, 20% sugar, plain water, 5% salt, or quinine (at a concentration of 1 millimolar) – and recorded their reactions.
Prof Andrew Barron, who researches insect behaviour at Macquarie University and who co-authored the paper, said under normal conditions the bees displayed something called “post-consumption glossa” after tasting the sweet solution: they kept on licking even after they’d finished drinking.
In contrast, they showed clear distaste for salt or quinine solutions.
“Facial expressions are an important window into the internal states of animals,” he said. “What we found is that bees show responses with their mouthparts to solutions that indicate their subjective like or dislike of those solutions. It tells us there is an inner life to the insect.”
Without language, evidence for pleasure or pain is challenging to establish in other animals. So scientists study behavioural markers, such as facial expressions, to gauge positive and negative experiences.
Previous studies have shown that mammals, such as primates and rats, display clear signs of “liking” such as licking and sticking out their tongues, and “disliking”.
“If a rat gets a salty taste it doesn’t like, it wipes its mouth parts, wipes its whiskers, wipes its tongue,” Barron said. “And we see something similar in a bee.”
But while similar findings in mammals were readily accepted, in insects such as bees the concept of an inner life remained “highly controversial”, he said.
To make sure they were not just observing a chemical reflex, the scientists tested responses with 18 colonies under a range of circumstances, including when the bees were heat-stressed, already full, or given doses of different drugs.
The bees’ reactions depended on context. For example, heat exposure changed their response to water or salty solutions from neutral or averse reactions to positive.
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It is as if someone had offered you an electrolyte drink, Barron said. “You’d probably go ‘blegh’ most of the time. Unless you’ve just been out on a really, really hot day, and done an enormous run, in which case an electrolyte drink is exactly what your body needs and it tastes fantastic.”
Associate Prof Thomas White, an entomologist from the University of Sydney who was not involved in the paper, said research into insect behaviour and sentience was “a fast moving field”.
What made this study fascinating was its focus on the “positive side of life”, he said, as the vast majority of research investigated negative feelings, such as pain or fear.
“The picture is increasingly pushing towards a view that insects, or many insects, have some simple capacity to feel the world, not just to assess it and detect it and process information but to actually have a point of view,” White said.
That was challenging for some people, he said. “It cuts against a lot of people’s intuition about where we might draw the line in the animal kingdom, as to what can feel pleasure and pain, and hence the kind of ethical and moral responsibilities we have towards those animals.”
Barron said: “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.”
