Bees navigate by the sun 鈥� so how do they manage when it鈥檚 cloudy? It turns out that they read clues to the hidden sun鈥檚 position in polarised light 鈥� as did the Vikings, according to one theory.
叠别别蝉鈥� eyes can see the orientation of polarised light. Because sunlight passing through the atmosphere takes on a characteristic polarisation pattern that reveals the location of the sun, it has long been suspected that bees use their eyes鈥� special photoreceptors to navigate when the sun is masked by cloud, says of the University of Queensland in Brisbane, Australia. Now he says he has 鈥渢he ultimate proof鈥� that this theory is correct.
He and his team created a simple 鈥渕aze鈥� of four tunnels arranged in a cross, and flooded two of the corridors with light polarised parallel to the length of the corridor, the other two with light polarised perpendicularly to the corridor.
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They then trained some 40 bees to enter the maze through one corridor and exit via a second that had a sugar reward at its end 鈥� the corridor to the right of the entrance corridor. Both the entrance and the 鈥渃orrect鈥� exit corridors were lit with light polarised perpendicularly to the corridor鈥檚 length 鈥� the light in the corridors to the left and straight ahead were filled with light polarised the other way.
Sugar free
After training, Srinivasan removed the sugar. The bees continued to choose the 鈥渃orrect鈥� corridor 鈥� the right-hand one 鈥� 74 per cent of the time on average. Of those that didn鈥檛, 15聽per cent flew straight ahead and 11聽per cent turned left.
But when the team changed the lighting so that the corridor straight ahead carried the pattern characteristic of the 鈥渃orrect鈥� exit, most of the bees 鈥� 56 per cent 鈥� opted to exit here instead. The number choosing the right-hand corridor dropped to 31 per cent 鈥� the remaining 13 per cent turned left.
Switching the 鈥渃orrect鈥� polarisation pattern again 鈥� this time to the left-hand corridor 鈥� changed the bees鈥� behaviour once more, encouraging 51 per cent of the bees to take the left route out of the maze. Just 14聽per cent flew straight ahead, and 34聽per cent turned right.
The bees read and stay 鈥渇aithful鈥� to the polarisation patterns, which they seem to have associated with the sugar reward, says Srinivasan.
Adrian Dyer, a vision scientist at Royal Melbourne Institute of Technology, Australia, says bees are already known to navigate using landmarks, smells and distance sensors 鈥� the new study 鈥渃learly shows鈥� they also use the polarisation of light, he says.
鈥淚t is incredible how such a small brain can incorporate so much sensory information to carry out complex navigational tasks,鈥� he says.
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