New research has found that bumblebees can have "emotion-like states," which suggests that insects may have more complex brains than previously thought.

"Insects are not as behaviourally rigid as we commonly and popularly think — they have some amazing cognitive capacities," said Clint Perry, a cognitive neuroethologist and lead author of the study, published today in the journal Science.

"And these so-called complex behaviours that are usually attributed uniquely to humans can be found in insects."

Perry and the other researchers from Queen Mary University of London didn't exactly find that bees have emotions, but they found that they have some criteria for them.

Feelings and emotions are complicated — they're reliant on a number of physiological, biological and cognitive factors. It's so complex that Perry said we can't even subjectively say whether humans have feelings without a verbal report.

But bees can't talk, so the researchers made several tests to analyze the insects' behaviour, and inferred their emotion-like states from what they did during those tests.

"In humans, our emotions affect the way we view things. If we're happy, then we're going to look at an ambiguous event more positively, and if we're anxious or depressed then we're going to look at the same event as more negative," said Perry.

They used that logic to design the tests for the bumblebees, which Perry said are incredibly intelligent, despite having brains the size of a sesame seed.

Judgment bias and attack tests

The two main tests were what Perry called a judgment bias test and a simulated predator attack test.

And the main ingredient was sugar.

"Sweet foods often improve our negative moods and can actually reduce crying in infants in response to negative events," said Perry.

Crab spiders often attack bumblebees in the wild, but the bees often get away. The research team simulated a crab spider attack for one of their tests. (Clint J. Perry)

They trained the bees to find food at a blue flower, and no food at a green flower. The bees quickly learned to fly to the blue flower and ignore the green one.

Then the researchers introduced a blue and green flower — meaning it would be ambiguous to the bees.

They gave half the bees a small amount of sugar water before the test. The bees that got the sugar flew more quickly to the ambiguous flower than the ones that had nothing before the test.

Perry said that demonstrated that the bees receiving the sugar before the test were more likely to perceive the ambiguous event as positive, much like how emotions affect human decision-making.

In the predator attack, the bees were trapped by a sponge mechanism for three seconds in order to simulate an attack by a crab spider, which happens in the wild.

Again, half the bees were given sugar water before the test. The bees that had gotten the sugar water beforehand recovered more quickly.

"They re-initiated foraging in a much shorter time than the bees that didn't receive the pretest reward," he said. "And this indicates that in an entirely different setup, this sucrose was causing a positive emotion-like state change."

The researchers say their findings can help us to understand how emotions have evolved, as well as the basic, underlying features of emotions in the brains of all animals.