String pulling bees provide insight into spread of culture

A bumblebee pulling a string. Credit: Olli Loukola

Pulling strings to obtain food is an experiment often used to test the intelligence of apes and birds, but it is the first time this technique has been discovered in an insect.

Moreover the cultural spread of such a technique from a single informed individual has also been described for the first time in an invertebrate animal.

The results, published in PLOS Biology, show that rare innovator bees were able to solve the problem of pulling the string to reach a sugar water reward by themselves while most others could learn to pull the string when trained.

Naïve bees were then able to learn the task by observing a trained demonstrator bee while this skill was passed down through several generations of learners, ensuring its longevity in the population.

Dr Sylvain Alem, lead author of the study, said: “We found that when the appropriate social and ecological conditions are present, culture can be mediated by the use of a combination of simple forms of learning. Thus, cultural transmission does not require the high cognitive sophistication specific to humans, nor is it a distinctive feature of humans.”

Dr Clint Perry, another lead author of the study, added: “Despite the obvious differences between humans and other animals, understanding social learning and culture in animals holds a key to understanding the evolutionary roots of the peculiarities of social learning and culture in humans.”

To test the bees’ capacity for learning string pulling, they were presented with three artificial blue flowers with a string attached to each flower and placed under a small transparent Plexiglas table.

Initially 23 bees, of a group of 40, were able to be trained in a stepwise manner by placing the flowers and strings at progressively distant positions under the table. Another group of bees were given the opportunity to solve the task spontaneously, without any training, and only two of 110 were successful suggesting it is a rare occurrence.

Naïve bees were then allowed to observe trained bees pulling the string from a distance and 60 per cent of them successfully learned the skill. Finally trained bees were placed in colonies and researchers observed that the technique spread successfully to a majority of the colony’s worker bees.  

Professor Lars Chittka, project supervisor, said: “We are ultimately interested in finding out what might be possible neural solutions to underpin such refined skills in bees. How can they do it with such small brains, and how can their miniature nervous systems manage such a diversity of behaviours and cognitive tasks?

“We are exploring this through modelling information processing in parts of the insect brain, and we find that often, exceedingly difficult tasks, for example in visual pattern recognition or floral scent learning, can be solved with extremely simple neural circuits. We are still a long way from understanding the required neural circuitry for string-pulling, however.”

The findings add to the accumulating evidence suggesting that the capacity of culture may be within most animals with a relatively basic toolkit of learning processes, in turn shedding light on the evolutionary precursors of the more sophisticated forms of culture in humans.

More information:
• Research paper: ‘Associative Mechanisms Allow for Social Learning and Cultural Transmission of String Pulling in an Insect’. Sylvain Alem, Clint J Perry, Xingfu Zhu, Olli J Loukola, Thomas Ingraham, Eirik Søvik, Lars Chittka. PLOS Biology.