A bumblebee hive鈥檚 thermostat is controlled by a strict division of labour, a new study has revealed.
Bumblebees warm and cool their hives to keep the brood of the next generation at just the right temperature 鈥� between 28掳C and 32掳C. When temperatures get too hot, they cool them by fanning their wings. And when it gets chilly, the bees vibrate their wing muscles to shunt heat down to their abdomen, which they hold up against larvae-containing comb. Watch a video of two incubator bees warming a brood cell (centre of the frame) while other workers move about around them. The bees were tagged for the purpose of the experiment.
鈥淵ou can see them shiver to transfer the heat,鈥� says Sean O鈥橠onnell of the University of Washington in the US.
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O鈥橠onnell and his colleagues filmed three Bombus huntii colonies. The team artificially changed the temperature, pushing it up to 38.6掳C and down as low as 10.3掳C. When temperatures got too hot, the shivering, incubating bees backed away from the brood to leave fanning bees to cool the larvae.
Conversely, the incubating bees compensated for drops in temperature by increasing the time they spent incubating.
Task switchers
The researchers then removed most of the incubating bees. Contrary to expectations, the fanning bees did not switch to incubating. Instead, within 24 hours of their colleagues being removed, the remaining incubating bees took over the temperature regulation on their own by increasing the time they spent shivering heat down onto the brood.
鈥淭ask switching was previously thought to be common among bumblebee workers,鈥� says O鈥橠onnell. 鈥淏ut this study indicates that there is strong specialisation in labour among individuals.鈥�
A bee鈥檚 body size seems to play a role in determining whether it becomes an incubator or a fanner.
鈥淲e expected that larger workers would be incubators, but we found to our surprise the opposite was true,鈥� says O鈥橠onnell said. 鈥淲e don鈥檛 know whether the smaller bees are really better at warming the nest, or whether the larger bees avoid incubating for other reasons. In general, larger bumblebee workers are foragers for food so they could be committed to that task.鈥�
Journal reference: Behavioral Ecology and Sociobiology (DOI: 10.1007/s00265-006-0309-7)
