Bees seem to show when they are pleased and like something, rather than just needing it, in one of the strongest signs yet that insects have subjective experiences.
In recent decades, it has become clear that bees are capable of more complex behaviours than we previously thought, such as counting and demonstrating a sense of rhythm. But discerning whether they have inner states akin to our emotions is more difficult. For one thing, insects don鈥檛 have the flexible facial musculature of mammals, which we use to communicate our feelings.
鈥淗ow can we get any behavioural readout of these insects with a hard body and their mask of a face,鈥� asks at Macquarie University in Sydney, Australia. 鈥淒o bees have any sort of inner state whatsoever?鈥�
Advertisement
To solve the mystery, Barron and his colleagues ran a series of experiments involving buff-tailed bumblebees (Bombus terrestris).
First, the team offered the bees a water droplet containing sugar, along with others that contained salt and quinine, while filming them using high-resolution video.
After tasting the sweet liquid, the bees repeatedly stuck out their glossa, which is a hairy tongue that they use to lap up nectar in flowers. After tasting the salty and bitter samples, the bees wiped their mouths and shook their heads.
However, both responses may have just been a reaction to the different chemicals, rather than a sign of enjoyment or displeasure, says Barron.
Next, the researchers reduced the concentration of the sugar and mixed it with a small amount of salt, resulting in a dramatic reduction of the glossa protrusions. Then they exposed the bees to 40掳C (104掳F) temperatures to dehydrate them, after which, when the bees were offered salty droplets, the bees repeatedly protruded their glossa.
鈥淚f I just handed you an electrolyte drink right now, you鈥檇 probably think, 鈥榳ell, that actually tastes pretty foul鈥�,鈥� says Barron. 鈥淏ut if you had just come back from a long run and I handed you an electrolyte drink, you鈥檇 think, 鈥榯hat鈥檚 fantastic鈥�. It鈥檚 because your internal state has changed, and that internal state is changing your evaluation of things 鈥� that鈥檚 what we think we鈥檙e seeing in the bees.鈥�
For the final part of their experiment, the researchers wanted to determine what would happen if they meddled with the chemistry that, in mammals, underpins appetite and the enjoyment of food.
When the bumblebees were treated with dopamine, which in mammals affects the motivation to seek food, their glossa protrusions didn鈥檛 increase, suggesting that although they had greater desire, their enjoyment 鈥渢ell鈥� 鈥� tongue protrusions 鈥� didn鈥檛 change.
But when the bees were treated with endocannabinoids, which increases the 鈥渓iking鈥� of food in mammals, it led to an increase in their glossa protrusions.
鈥淲hat this is showing us is that even from an animal like a bee, there is some sort of inner life for that insect,鈥� says Barron. 鈥淭here鈥檚 something going on. It鈥檚 evaluating its world. It鈥檚 experiencing its world and it鈥檚 not a robotic entity running on a program.鈥�
at the California Institute of Technology says the research is 鈥渁n important and innovative study on a difficult topic鈥�. 鈥淭he evidence presented in the paper shows that the bees represent the value of the taste stimuli in a flexible manner,鈥� he says. But it is unclear whether the experiments demonstrate pleasure as we know it.
鈥淭he 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,鈥� he says. 鈥淚 think we should conclude that bees have bee emotions, not mammal emotions.鈥�
at the London School of Economics says the study is the first time he has 聽seen 鈥渨anting鈥� and 鈥渓iking鈥� disentangled in a bee.
鈥淲e underestimate insects so much,鈥� he says. 鈥淚t鈥檚 led to a golden age of very charming studies where scientists use modern techniques 鈥� sometimes just high-resolution, high-frame-rate video, as in this study 鈥� to reveal behaviours people have been missing.鈥�
PNAS
