Honeybees have become the first invertebrates to exhibit pessimism, a benchmark cognitive trait supposedly limited to "higher" animals.

If these honeybee blues are interpreted as they would be in dogs or horses or humans, then insects might have feelings.

Honeybee response "has more in common with that of vertebrates than previously thought," wrote Newcastle University researchers Melissa Bateson and Jeri Wright in their bee study, published June 2 in Current Biology. The findings "suggest that honeybees could be regarded as exhibiting emotions."

Bateson and Wright tested their bees with a type of experiment designed to show whether animals are, like humans, capable of experiencing cognitive states in which ambiguous information is interpreted in negative fashion.

Of course, unlike unhappy people, animals can't say that the glass is half-empty. Researchers must first train them to associate one stimulus — a sound, a shape, or for honeybees, a smell — with a positive reward, and a second with a punishment.

Then, by prompting the animals with a third, in-between stimulus, it's possible to assess their outlook. Like a depressed person seeing hostility in a neutral gaze, pessimistic animals tend to treat that uncertain stimulus like a punishment.

Such tests might seem simplistic compared to the richness of human emotion, but they're the most objective available tool for comparing cognition across species. And pessimism is no mean feat: It's a form of cognitive bias, considered in humans to be an aspect of emotion. You can't be pessimistic if you don't have an inner life.

'I don't think it's a stretch to say that they are tapping into bee emotions.'Earlier research has found rats and dogs capable of pessimism. Bateson has also documented pessimism in starlings. But though honeybees have passed tests of pattern recognition and spatial modeling, the idea of feelings occurring in their sesame-seed-sized brains is generally considered unlikely, if not downright laughable.

"Invertebrates like bees aren't typically thought of as having human-like emotions," said Bateson, yet honeybees and vertebrates share many neurological traits. "Way, way back, we share a common ancestor. The basic physiology of the brain has been retained over evolutionary time. There are basic similarities."

Until now, though, they hadn't been tested. Bateson and Wright trained their honeybees to associate one scent with a sugary reward and another scent with bitterness. Then they shook half their beehives, mimicking a predator attack. Afterwards, shaken bees still responded to the sugary scent, but were more reluctant than their unshaken brethren to investigate the in-between smell.

Further analysis of the shaken bees' brains found altered levels of dopamine, serotonin and octopamine, three neurotransmitters implicated in depression. In short, the bees acted like they felt pessimistic, and their brains looked like it, too.

"The methodology is sound," said Lori Marino, an Emory University evolutionary neurobiologist who was not involved in the study. "I don't think it's a stretch to say that they are tapping into bee emotions. After all, every animal has to have emotions in order to learn and to make decisions. And we already know from many other studies that bees are really cognitively sophisticated."

But Bateson said the results could be interpreted another way. "Either bees have feelings, or cognitive bias isn't as tightly correlated with feelings as we thought," she said. "Maybe cognitive bias is not a good measure of emotion."

In future studies, Bateson hopes to elicit from honeybees other forms of apparent emotion, such as happiness. She also wonders about the mental effects of chemicals and disease.

"It would be interesting to know if pesticides were altering their cognition, creating states similar to depression," she said.

Image: Jack Wolf/Flickr

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Citation: "Agitated Honeybees Exhibit Pessimistic Cognitive Biases." By Melissa Bateson, Suzanne Desire, Sarah E. Gartside, and Geraldine A. Wright. Current Biology, June 2, 2011.