October 6, 2016 – Did you know ‘string pulling’ is a popular problem-solving task for investigating cognitive abilities in most animals? But it had never been tested in insects. Now new research has revealed bumble bees can learn how to pull a string to get a sugar water reward.

Researchers from Queen Mary University of London, UK also found bees learn how to get the reward by watching others do it, and the new skill continues to spread through a colony even after the original string-puller is gone.

Social learning facilitates the transmission of behaviours from individual innovators to a group, and is common among animals, from birds to rodents to primates. To test social learning in an insect, Lars Chittka and colleagues attached strings to artificial flowers laden with sugar water, put these ‘flowers’ under Plexiglas, and trained bumblebees to pull strings to access the sugar water.

“What I like about the work,” said Lars, “In addition to the experimental and intellectual challenges and insights, is the sheer absurdity of seeing bees solving a string-pulling puzzle. When lead author Sylvain Alem first showed me a bee successfully pulling on the string, I just couldn’t believe what I was seeing. And even now, looking at the videos still makes me laugh.”


The trained bees served as innovators. To see if other bees could learn from them, the researchers put 25 untrained bees in transparent cages where they could watch trained bees demonstrate their string-pulling prowess. Untrained bees rarely learned this skill on their own. But 60% of the untrained bees solved the problem after watching other bees do it, showing that they can learn socially.

To test whether string pulling would also be transmitted culturally in bumblebees, the researchers added a single trained bee to each of three colonies of untrained bees. Then the researchers assessed string pulling in pairs of bees. After 150 of these bouts, roughly half of the untrained bees in each colony had learned to pull strings to get sugar water (53%, 58% and 42% respectively for the three colonies). Moreover, even though the trained innovator died after only about a third of the test bouts in one colony, string pulling continued to spread, underscoring the strength of this cultural transmission.

“It was even more of a surprise that not only could bees be trained to solve this task in a step-by-step manner – but a small minority of bees actually solved the task by themselves, without gradual training or observing a skilled bee. The final big surprise came in the context of social learning: we discovered that naive individuals that would observe, from a distance, a skilled string-pulling bee, could subsequently solve the task by themselves,” said Lars.

This work shows that social learning and cultural transmission can occur in animals with a cognitive toolkit far simpler than that of humans.

“How much brainpower is actually required for any one task – how many neurons, how many sequential and parallel neural processing stages?” asked Lars. “In that view, the single task that actually requires a big brain has not been discovered yet, and indeed there is more and more evidence, both from experiments on small-brained insects and computational neuroscience, that small circuits can deal with exceptionally complex challenges.”

The research was published this week in PLOS Biology.

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