The honeybee's tongue (glossa) is covered with bushy hairs and resembles a mop or a brush. We examined the dimensions of glossal hairs of the Italian honeybee (Apis mellifera ligustica) and found that the average length of hairs increased from the proximal segment to the distal end. The glossal dynamic surface of a honeybee in drinking cycles was captured by a specially designed high-speed camera system, and we discovered that the glossal hairs erected rhythmically when drinking nectar; specifically, hairs on the proximal segment erected earlier than those on the distal end of a honeybee's tongue, which was identified as the phenomenon of asynchronous hair erection. Moreover, by measuring the wettability of the tongue, we found that the flabellum was the most hydrophilic and the root of the tongue was hardest to be wetted. According to our observations, we suggest that the honeybee has an optimal hair-erection pattern that could balance nectar intake and viscous drag. These results will be helpful to understand the liquid-feeding mechanism of honeybees, especially the role of erectable glossal hairs.

Most flower-visiting insects employ highly-evolved organs to feed themselves rapidly and efficiently on the floral nectar. A honey bee drives its segmented tongue (glossa) covered by dense hairs reciprocatingly to load nectar. A high-speed camera system ameliorated by a microscope revealed morphological changes in glossal surfaces during live honey bees' nectar dipping and surface configurations through the stretching of postmortem honey bees' glossae. Both the in vivo and postmortem observations reveal that shortening and lengthening of the glossal segments perform high concordance with the erection of glossal hairs, which aids in developing deformable gaps between rows of glossal hairs during nectar trapping. A model was proposed to evaluate the nectar-intake volume considering the experimentally-measured average erection angle and tongue elongation length during nectar feeding. The theoretical results fit the experimental data well and disclose that these two factors contribute to an augmentation of nectar-intake observably. We also theoretically present that the extendible and deformable glossae have advantages for the polylectic feeding behavior.

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