Bumblebees actively cool themselves during hovering using their own wingbeats. The downward airflow they generate themselves is essential to prevent overheating. Without this self-induced airflow, hovering bumblebees would overheat within a minute and a half under a range of conditions, researchers report in Proceedings of the Royal Society B of 18 February.
The researchers measured the wingbeat and the speed of the induced airflow in freely hovering workers of Bombus impatiens. This ranged from 0.19 to 1.22 metres per second, with a mean of 0.53 metres per second. In a vertical wind tunnel, they then determined how much heat such airflows can dissipate via convection – heat loss through air movement – and incorporated these data into thermal models.
In simulations at 25 degrees Celsius, the body temperature of both small and large bumblebees stabilised within the functional flight range of 28 to 42 degrees Celsius. When the contribution of the self-induced airflow was removed from the model, all simulated bumblebees overheated within a minute and a half.