By Sid Perkins
The electric fields that build up on honey bees as they fly, flutter their wings, or rub body parts together may allow the insects to talk to each other, a new study suggests. Tests show that the electric fields, which can be quite strong, deflect the bees' antennae, which, in turn, provide signals to the brain through specialized organs at their bases.
Scientists have long known that flying insects gain an electrical charge when they buzz around. That charge, typically positive, accumulates as the wings zip through the air—much as electrical charge accumulates on a person shuffling across a carpet. And because an insect's exoskeleton has a waxy surface that acts as an electrical insulator, that charge isn't easily dissipated, even when the insect lands on objects, says Randolf Menzel, a neurobiologist at the Free University of Berlin in Germany.
Although researchers have suspected for decades that such electrical fields aid pollination by helping the tiny grains stick to insects visiting a flower, only more recently have they investigated how insects sense and respond to such fields. Just last month, for example, a team reported that bumblebees may use electrical fields to identify flowers recently visited by other insects from those that may still hold lucrative stores of nectar and pollen. A flower that a bee had recently landed on might have an altered electrical field, the researchers speculated.
Now, in a series of lab tests, Menzel and colleagues have studied how honey bees respond to electrical fields. In experiments conducted in small chambers with conductive walls that isolated the bees from external electrical fields, the researchers showed that a small, electrically charged wand brought close to a honey bee can cause its antennae to bend. Other tests, using antennae removed from honey bees, indicated that electrically induced deflections triggered reactions in a group of sensory cells, called the Johnston's organ, located near the base of the antennae. In yet other experiments, honey bees learned that a sugary reward was available when they detected a particular pattern of electrical field.
Altogether, these tests suggest that the electrical fields that build up on bees due to their flight or movement are stimuli that could be used in social communication, the researchers report online this week in the Proceedings of the Royal Society B.
The team's findings "are very significant," says Fred Dyer, a behavioral biologist at Michigan State University in East Lansing. "I hadn't heard about the possibility that honey bees could use electrical fields."
One of the honey bees' forms of communication is the "waggle dance." When the insects have located a dense patch of flowers or a source of water, they skitter across the honeycomb in their hive in a pattern related to the direction of and the distance to the site. Fellow worker bees then take that information and forage accordingly. The biggest mystery about the dance, Dyer says, is which senses the bees use—often in the deep, dark recesses of their hive—to conduct their communication. "People have proposed a variety of methods: direct contact between bees, air currents from the buzzing of their wings, odors, even vibrations transmitted through the honeycomb itself," he says.
But the team's new findings introduce yet another mode of communication available to the insects, Dyer says. He notes that the group found that antenna deflections induced by an electrically charged honey bee wing are about 10 times the size of those that would be caused by airflow from the wing fluttering at the same distance—a sign that electrical fields could be an important signal.
"They show that the electrical fields are there and that they're within the range of what the animal can sense," Dyer says. "Their claim of evidence is quite compelling."