Bees learn to read simple ‘Morse code’

Biology Letters study shows that bumblebees can be trained to differentiate between long and short light flashes 

Researchers at Queen Mary University of London have shown for the first time that an insect – the bumblebee Bombus terrestris – can decide where to forage for food based on different durations of visual cues.  

In Morse code, a short duration flash or ‘dot’ denotes a letter ‘E’ and a long duration flash, or ‘dash’, means letter ‘T’. Until now, the ability to discriminate between ‘dot’ and ‘dash’ has been seen only in humans and other vertebrates such as macaques or pigeons.  

PhD student Alex Davidson and his supervisor Dr Elisabetta Versace, Senior Lecturer in Psychology at Queen Mary, led a team that studied this ability in bees. They built a special maze to train individual bees to find a sugar reward at one of two flashing circles, shown with either a long or short flash duration. For instance, when the short flash, or ‘dot’, was associated with sugar, then the long flash, or ‘dash’, was instead associated with a bitter substance that bees dislike.  

At each room in the maze, the position of the ‘dot’ and ‘dash’ stimulus was changed, so that bees could not rely on spatial cues to orient their choices. After bees learned to go straight to the flashing circle paired with the sugar, they were tested with flashing lights but no sugar present, to check whether bees’ choices were driven by the flashing light, rather than by olfactory or visual cues present in the sugar.   

It was clear the bees had learnt to tell the light apart based on their duration, as most of them went straight to the ‘correct’ flashing light duration previously associated with sugar, irrespective of spatial location of the stimulus. 

Alex Davidson said: “We wanted to find out if bumblebees could learn to the difference between these different durations, and it was so exciting to see them do it”. 

“Since bees don’t encounter flashing stimuli in their natural environment, it’s remarkable that they could succeed at this task. The fact that they could track the duration of visual stimuli might suggest an extension of a time processing capacity that has evolved for different purposes, such as keeping track of movement in space or communication”. 

“Alternatively, this surprising ability to encode and process time duration might be a fundamental component of the nervous system that is intrinsic in the properties of neurons. Only further research will be able to address this issue.” 

The neural mechanisms involved in the ability to keep track of time for these durations remain mostly unknown, as the mechanisms discovered for entraining with the daylight cycle (circadian rhythms) and seasonal changes are too slow to explain the ability to differentiate between a ‘dash’ and a ‘dot’ with different duration.  

Various theories have been put forward, suggesting the presence of a single or multiple internal clocks. Now that the ability to differentiate between durations of flashing lights has been discovered in insects, researchers will be able to test different models in these ‘miniature brains’ smaller than one cubic millimetre. 

Elisabetta Versace continued: “Many complex animal behaviours, such as navigation and communication, depend on time processing abilities. It will be important to use a broad comparative approach across different species, including insects, to shed light on the evolution of those abilities. Processing durations in insects is evidence of a complex task solution using minimal neural substrate. This has implications for complex cognitive-like traits in artificial neural networks, which should seek to be as efficient as possible to be scalable, taking inspiration from biological intelligence.”