Our atmosphere is permeated by invisible electric fields - they are created by thunderstorms, clouds or even volcanic eruptions and dust storms. However, as scientists have now discovered, swarms of insects can also charge the air electrically. According to their measurements, for example, a potential gradient of 100 to 1000 volts per meter occurs in swarms of bees. Large swarms of locusts can even charge the air to a similar extent and over a large area as meteorological events. According to the researchers, this shows that such electric fields can arise not only from purely physical influences, but also from biological life forms and their behavior.
If the air before a thunderstorm often seems charged, that's no illusion: storm clouds and other weather phenomena actually create static electric fields in the atmosphere. They form because zones of different charges are created in the clouds. During a thunderstorm, such potential gradients are usually discharged by lightning. In the eruption clouds of volcanoes or in dust storms, the interaction of suspended particles can also lead to charge separation and electrical charging. Sometimes flashing lightning bears witness to this. "But the Earth's atmosphere is always electrified to a greater or lesser degree, even when the weather is nice and at some distance from thunderstorms," explain Ellard Hunting of the University of Bristol and his colleagues. These electric fields play an important role in weather and atmospheric transport processes and can also affect the migration of biological organisms.
Honey bees as charge carriers
"So far, we've always looked at how different organisms use these static electric fields that are present almost everywhere in the environment," explains Hunting. So far, the influence of physics on biology has always been examined, but not vice versa. Hunting and his team have now changed that. They wanted to know whether insects and especially swarms of insects can electrically influence their local environment. "Many species of flying insects have already been shown to be able to carry an electrical charge in the range from a few picocoulombs to nanocoulombs," the scientists explain. To find out how this changes the potential gradient of the air, they first carried out measurements with several honey bee swarms. To do this, they placed an electric field meter and an upward-pointing camera on the ground while the swarm of bees flew overhead.
The measurements showed that the potential gradient in the air space above the measuring device changed significantly during the passage. "The potential gradient rose to 100 volts per meter at the moment of the greatest swarm density," report Hunting and his colleagues. Measurements with other swarms of bees even resulted in values of up to 1000 volts per meter. The denser the swarm of bees, the stronger the electric fields they generated. "These measurement data indicate that a honey bee swarm contains enough charges to influence the atmospheric potential gradient proportional to the swarm density," the researchers state. This also applies to other swarming insects such as termites, ants, mosquitoes or grasshoppers.
In the extreme as strong as meteorological phenomena
In order to be able to determine the achievable extent of the electrifying influence of such swarms of insects, the team developed a special model with which they could calculate the strength of the electric fields based on the swarm density and size of the insect. Based on published values for large swarms of migratory locusts, Hunting and his colleagues came up with values whose magnitude is comparable to that of meteorological causes. "Our calculations show that swarms of migratory locusts can even reach charge densities that can exceed those of electrical storms and clouds," the scientists write. In contrast, the butterflies, which usually only migrate in very loose, much less dense swarms, have a much smaller influence on atmospheric electricity.
"Our results suggest that large assemblages of insects are a previously unrecognized source of electrical variability in the atmosphere," Hunting and his team explain. They also suspect that other organisms such as bacteria or birds can also electrically change the air around them. "This discovery has significant implications for several physically and biologically relevant areas," the team said. Because these electric fields generated by organisms can influence the transport of dust, pollen or aerosols in the atmosphere. "There are many underexplored connections between biology and static electric fields, ranging in spatial scale from microbes in the soil to pollinator interactions with plants to large swarms of insects," says Hunting. There is still a lot to be researched into the dynamic interactions between physics and biology in the atmosphere.
Source: Ellard Hunting (University of Bristol) et al., iScience, doi: 10.1016/j.isci.2022.105241