Bumblebee facial movements give clues to their inner lives

Bees exhibit behavior that suggests they not only need, but also enjoy certain things, indicating they may have subjective experiences.

In the past few decades, it’s been revealed that bees can perform complex tasks like counting and keeping rhythm. However, understanding whether they possess emotions similar to humans is challenging, partly because they lack the expressive facial muscles mammals use for emotional communication.

“How can we get any behavioural readout of these insects with a hard body and their mask of a face,” wonders Andrew Barron from Macquarie University in Sydney, Australia. “Do bees have any sort of inner state whatsoever?”

To explore this, Barron and his team conducted experiments with buff-tailed bumblebees (Bombus terrestris).

Initially, they presented the bees with a water droplet containing sugar, as well as others with salt and quinine, capturing their reactions on high-resolution video.

When sampling the sweet liquid, the bees extended their glossa, a hairy tongue used for sipping nectar. In contrast, after trying the salty and bitter solutions, they wiped their mouths and shook their heads.

Yet, Barron notes these reactions might simply be responses to the chemicals rather than indicators of pleasure or displeasure.

In the next phase, they decreased the sugar concentration and added some salt, which significantly reduced the glossa extensions. Upon dehydrating the bees at 40°C (104°F) and then offering salty droplets, the bees once again extended their glossa.

“If I just handed you an electrolyte drink right now, you’d probably think, ‘well, that actually tastes pretty foul’,” says Barron. “But if you had just come back from a long run and I handed you an electrolyte drink, you’d think, ‘that’s fantastic’. It’s because your internal state has changed, and that internal state is changing your evaluation of things – that’s what we think we’re seeing in the bees.”

In the final experiment, the researchers examined how altering the chemistry related to appetite and food enjoyment in mammals would affect the bees.

When bumblebees were exposed to dopamine, which in mammals relates to the motivation to seek food, there was no increase in glossa protrusions. This suggests that while their desire might have increased, their enjoyment, as shown by tongue protrusions, didn’t.

However, when treated with endocannabinoids, which enhance food enjoyment in mammals, their glossa protrusions increased.

“What this is showing us is that even from an animal like a bee, there is some sort of inner life for that insect,” says Barron. “There’s something going on. It’s evaluating its world. It’s experiencing its world and it’s not a robotic entity running on a program.”

Ralph Adolphs from the California Institute of Technology considers the research “an important and innovative study on a difficult topic”. He notes that the evidence indicates bees can flexibly value taste stimuli, though it’s uncertain if this equates to experiencing pleasure as humans do.

“The idea that facial expressions are literally constitutive of emotions is clearly not the case. Actors can fake them, and people whose faces are paralysed still have emotions,” he says. “I think we should conclude that bees have bee emotions, not mammal emotions.”

Jonathan Birch at the London School of Economics mentions this study as the first instance of distinguishing between “wanting” and “liking” in bees.

“We underestimate insects so much,” he says. “It’s led to a golden age of very charming studies where scientists use modern techniques – sometimes just high-resolution, high-frame-rate video, as in this study – to reveal behaviours people have been missing.”