Erection pattern and section-wise wettability of honeybee glossal hairs in nectar feeding.

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.