Queen bumblebees are poor foragers thanks to sparse tongue hair

Queen bumblebees have a newfound excuse for slacking on foraging nectar: Their tongues are holding them back.

Bumblebees have long, hairy tongues that help them lap up nectar from flowers. But queen bumblebee’s tongues are less efficient at collecting nectar than those of worker bees, researchers report January 12 in Proceedings of the National Academy of Sciences.

In the spring, when a queen bumblebee first emerges from her winter slumber, she initially fuels herself by guzzling nectar from flowers. But once she establishes a nest and her eggs hatch into worker bees, she delegates foraging duties to the workers.

Those workers may be better suited to the task, according to a close investigation of the tongues of buff-tailed bumblebees (Bombus terrestris). The bees’ tongues range in length from around 4 millimeters to 10 millimeters. The queens, who are bigger than the workers, tended to have longer tongues. But those longer tongues had relatively less hair, scanning electron microscope imagery revealed. And high-speed video of bumblebees feeding on artificial nectars revealed that queens’ tongues were less efficient at capturing the liquid.

The hairs, which are hundreds of micrometers long, trap the nectar on the tongue. The tongue “acts a bit like a microscopic sponge,” says Zexiang Huang of Sun Yat-Sen University in Shenzhen, China. “Many closely spaced hairs create countless tiny gaps that hold nectar by surface tension.” Sparser hair is less effective at trapping the liquid..

Other considerations probably also play a role in keeping the queens homebound, such as the need to care for their brood. But tongues are a previously unidentified factor in the divvying up of foraging duties.

Understanding the importance of the tongue’s hairy microstructure could be helpful for predicting how well various types of bees can harvest nectars of different concentrations and viscosities, says biophysicist Saad Bhamla of Georgia Tech in Atlanta, who was not involved with the research. That could be helpful information for bee breeders and apiaries, and relevant for managing pollination of crops.