May the Force be with the bee

By Athayde Tonhasca

If we are asked how a bee finds a flower, we think of smells, colours, shapes and textures. These are important sensory signals, but there is another one whose relevance is just beginning to be understood: electricity.

It has long been known that the platypus, some fish and amphibians, as well as some ants, cockroaches, mosquitoes and fruit flies have the ability to detect external electric forces. However, vertebrates need water as a conductive medium, while most insects respond only to unusually strong electric fields such as those generated by high voltage power lines. Bumble bees however have a sparking story to tell. 

We do not notice it, but our planet is an immense electrical circuit. On a calm day, the air is positively charged, while the ground surface has a negative charge. Now and then the equilibrium of charges is disturbed by lightning bolts or a minor shock from a car door, reminding us we are surrounded by electricity.

The negative charges accumulated on the planet’s surface extend to any object connected to the ground, plants included. So flowers have a slight negative charge in relation to the air around them. As a bee buzzes along in search of food, electrons are stripped off its body by friction with the air, leaving the bee positively charged. When the bee lands on a flower, some of the negatively charged pollen grains stick to the bee, sometimes jumping from the flower even before the bee makes contact. So electrostatic forces are a great aid to pollination.

An electrifying encounter: a positively charged bee approaches a negatively charged flower. Images in the public domain.
Pollen clinging to a sweat bee. © Pixabay.

But flower power reaches shocking levels for the buff-tailed bumble bee (Bombus terrestris), and probably for other bumble bees as well: they are able to sense the weak electric field around a flower. No one knows exactly how they do it, but mechanoreceptive hairs must be involved. These special hairs are innervated at their base, so they detect mechanical stimuli such as air movement and low frequency sounds. Apparently, the flower’s electrical field moves the mechanoreceptive hairs of an approaching bee, similar to the way a rubbed balloon makes your hair stand on end. This hair movement is processed by the bee’s central nervous system and gives information about the shape of the electric field. It is as if the bee ‘sees’ the flower’s electrical aura. 

Bumble bees’ hairs provide thermal insulation, collect pollen and help bees sense air motion, sounds and electricity. ©Kevin Mackenzie, University of Aberdeen. Attribution 4.0 International (CC BY 4.0).

But bumble bees’ capacity to detect electric forces may go beyond recognising flowers’ sizes and shapes: they could use the information to maximise foraging trips. Once a positively charged bee lands, the flower’s electric field changes and remains changed for about two minutes after the bee leaves. Researchers believe that an altered field warns the next bee that the flower is temporarily depleted of nectar; it’s like turning off a ‘we are open’ neon sign. So the next bee may as well buzz off to another flower with sufficient negative charges and a decent volume of nectar. 

Bees and other insects detect ultraviolet and polarized light, and use magnetic fields for navigation. Sensing electricity is one more way their world is experienced radically differently from ours.