As they fly through the air, bees – like all insects – acquire a positive electric charge. Flowers, on the other hand, are grounded and so have a negative charge. Daniel Robert at the University of Bristol, UK, and colleagues set out to investigate whether bumblebees (Bombus terrestris) were able to make use of these signals.
To test the idea, the team created artificial flowers, filling some with sucrose and others with quinine, a substance bees don't feed on. To start with, the bees visited these flowers at random. But when a 30 volt field – typical for a 30-centimetre-tall flower – was applied to the artificial blooms containing sucrose, the team found that the bees could detect the field from a few centimetres away and visited the charged flowers 81 per cent of the time. The bees reverted to random behaviour when the electricity was switched off.
"That was the first hint that had us jumping up and down in the lab," says Robert. The result suggests the bees may use the electric field as an indicator of the presence of food, much like colour and scent do. In the absence of a charge, they forage at random.
Next, his team looked at whether the bees were influenced by the shape of a flower's electric field, which is determined by the flower's shape. By varying the shape of the field around artificial flowers that had the same charge, they showed that bees preferentially visited flowers with fields in concentric rings like a bullseye: these were visited 70 per cent of the time compared to only 30 per cent for flowers with a solid circular field.