The observations are reported in the June 21 issue of Current Biology in a new paper by Elli Leadbeater and Lars Chittka of Queen Mary, University of London.
Bumblebees are highly social insects, but they do not recruit nestmates to feeding locations, and foragers have therefore been thought to rely mainly on individual experience when seeking out rewarding flowers. The role of other bees in these decisions has been considered only in the context of deterrence because the small scent marks that foragers leave after emptying flowers dissuade others from visiting.
In the new study, the researchers offered bumblebees the choice between several artificial-flower clusters in a laboratory setting. The bees preferred to feed from clusters where another bee was already collecting nectar, rather than making their own independent choices. Most interestingly, the bees only copied each other when they knew nothing about the flower species that they were visiting. When revisiting a flower species that they had tried before, they relied upon their own individual initiative.
It's not yet possible to say why bumblebees visit flowers that other bees are foraging on, but it could be that bees learn that the presence of another bee provides an efficient shortcut to success. These findings provide an intriguing new contribution to the ever-growing stack of evidence suggesting that insect foraging behavior is surprisingly complex.