SOCIAL insects are often dismissed as slaves to the collective mind of the hive. But individual members of colonies do have brains and are technically capable of making their own decisions. Indeed, several studies have shown that insects such as ants and bees sometimes ignore shared information in favour of what they individually know. What drives them to act independently has been something of a mystery. New research shows that when a tasty source of food is available the hive mentality is blatantly ignored.

The discovery was made when Ellouise Leadbeater, then of the Zoological Society of London, and Claire Florent of University College London were studying how bumblebees gathered nectar. Insects have various ways of sharing information. Ants obtain social information about food sources by following trails of chemicals left by the feet of other ants, and honeybees learn about resources by studying dances performed by their hive mates. Like them, bumblebees have their own technique. They learn about new supplies of nectar by monitoring the floral scents in their nesting colony and then searching for the smells outside. This led Dr Leadbeater and Ms Florent to speculate that if they meddled with the scents found in these colonies, they could find out what caused bumblebees to ignore social information in favour of their own knowledge.

To do this, the researchers gave 42 individually tagged bumblebees two days to explore an experimental garden. Within this garden were seven artificial flowers in the form of yellow foam discs laced with essential oils of geraniums and a small well containing 50 microlitres of a nectar-like sugar solution. After their orientation was complete, single bees were selected at random as they left to forage in the garden. Half of these bees, upon their return to the colony to deposit the nectar they collected, found the colony as they left it: rich with the smell of geranium oil. The other half, however, returned to a colony that had been artificially laced with essential oils of lavender, just as it would have been if their fellow hive members had been collecting nectar from lavender plants.

The fragrant garden

When the bumblebees next went out to forage in the garden they encountered not just the seven geranium-scented artificial flowers but also seven new artificial flowers laced with lavender oil. This time, only the lavender flowers contained a sugary solution. This represented a typical situation where some plant species come into bloom and others fade.

As before, all 42 bumblebees headed for the geranium-scented flowers, regardless of what scent they had encountered in their colony. Similarly, all but two of the bees made between six and eight geranium visits before deciding to take a chance with the lavender-scented ones.

As the researchers report in the July issue of Behavioural Ecology and Sociobiology, the social information gained from the colony seemed to play only a minor role in determining how quickly bumblebees switched to the lavender food source. If the bumblebees came from the lavender-scented colony, then once they had visited their first lavender plant, 80% of the flowers they subsequently visited were lavender. That compared with a figure of 60% for bumblebees that came from a colony where the scent of lavender was absent.

Precisely why the bumblebees largely ignored social information about lavender and so steadfastly stuck with their personal knowledge about geraniums providing a bigger feast, even when it was no longer so, proved vexing. Dr Leadbeater and Ms Florent wondered if the insects might have an innate preference for geraniums over lavender, but in a follow-up experiment where bumblebees were given the chance to choose between the two, they showed no preference whatsoever.

Dr Leadbeater speculates that learning a new foraging route might expose bumblebees to risks that they would not encounter if they simply returned to flowers that they had already personally visited, and that this is why they resisted following up on new foraging information. Bumblebee nests, it appears, buzz with a lot more individuality than anyone had realised.