Drag Reduction in the Mouthpart of a Honeybee Facilitated by Galea Ridges for Nectar-Dipping Strategy

Some nectarivorous animals have evolved highly specialized tongues to gather nectar from flowers. Here we show that the Italian honeybee, Apis mellifera ligustica, uses the uniformly-distributed ridges on the internal wall of the mouthpart to reduce drag while drinking nectar. We discovered that the tip of the tongue is covered with bushy setae and resembles a brush, and the ridges are parallel distributed on the inner wall of the galeae. Using high-speed camera, we recorded the morphology of the mouthpart when dipping the sucrose water. Considering the ridges and the movement rule of the glossa, we proposed a model for analyzing the mechanism of drag reduction. Theoretical estimation of the friction coefficient with respect to the dipping frequency indicates that the erectable bushy hairs and the ridges can significantly reduce friction when a honeybee drinks nectar. Results show that dimensions of the ridges play a key role in reducing friction. It can be concluded that the ridges on the galeae of honeybee's mouthpart can reduce the friction coefficient by 86% compared with the case of the transverse distribution coefficient S = 40. Finally, the capability of drag reduction in the mouthpart of honeybee may inspire a creative concept for designing efficient viscous micropumps.