Effects of tongue hair flexural deformation on viscous fluid transport by bees.

A bee's tongue is coated in dynamic hairs that gradually unfold to entrain the viscid nectar, during which hairs inevitably deflect as a result of fluid drag. The hair deflection induced decline in nectar capture rate may be a coupled elastoviscous problem and remains poorly understood. Here we employed geometric beam theory coupled with the effective viscous force to derive a dynamic model for a rotary tongue hair deflection in a viscous fluid. Considering deflection of the tongue hair, we rationalized the nectar capture rate by takingBombusterrestrisas a model system. When the nectar concentration increases from 20% to 70%, the nectar capture rate declines by 87%, indicating that hair erection is more severely impeded in thicker nectar. Based on this model, we predicted an optimal hair length with which the bee can reach the maximum nectar capture rate. This work may provide a new theoretical framework for quantifying viscous liquid transport by hairy surfaces and shed light on design methodologies for fluid transport devices using hairy beds.