May 21, 2024


How do insects charge the air?

Our atmosphere is permeated with invisible electric fields – created by thunderstorms, clouds, or even volcanic eruptions and dust storms. However, as scientists have now discovered, swarms of insects can also electrically charge the air. According to their measurements, for example, a potential gradient from 100 to 1000 volts per meter occurs in swarms of bees. Large locust swarms can 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 appears charged, this is not an illusion: storm clouds and other weather phenomena actually create static electric fields in the atmosphere. They form because regions of different charges are created in clouds. During a thunderstorm, such potential gradients are usually discharged by lightning. In volcanic eruptions or in dust storms, the interaction of suspended particles can also lead to charge separation and electrical charge. Sometimes flashing lightning testifies to this. “But Earth’s atmosphere is always more or less electrified, even when the weather is nice and at some distance from a thunderstorm,” explain Ellard Hunting of the University of Bristol and colleagues. These electric fields play an important role in air and atmospheric transport processes and can also affect the migration of organisms.

Honey bees as cargo carriers

“So far, we’ve always looked at how different organisms use these static electric fields that are almost everywhere in the environment,” Hunting explains. So far, the influence of physics on biology has always been examined, but not the other way around. Hunting and his team have now changed that. They wanted to know if insects and especially swarms of insects could electrically affect their local environment. The scientists explained that “several species of flying insects have already demonstrated their ability to carry an electric charge in the range of a few picocoulombs to nanocoulombs.” To see how this changes the potential gradient of air, they first made measurements with several honeybee swarms. To do this, they placed an electric field meter and an upward camera on the ground as a swarm of bees hovered overhead.

The measurements showed that the potential gradient in the airspace above the measuring instrument changed significantly during the passage. “The potential gradient rises to 100 eV per meter at the moment when the swarm is most intense,” Hunting and colleagues say. Measurements with other swarms of bees have resulted in values ​​as high as 1,000 volts per metre. The higher the density of the bee swarm, the stronger the electric fields it produces. “These measurement data indicate that the honeybee swarm contains sufficient charges to influence the potential atmospheric gradient proportional to swarm density,” the researchers stated. This also applies to other insects such as termites, ants, mosquitoes, or grasshoppers.

In extreme strength meteorological phenomena

In order to determine the achievable extent of the electrical effect of these insect swarms, the team developed a special model in which they could calculate the strength of electric fields based on swarm density and insect size. Based on published values ​​for large swarms of migratory locusts, Hunting and colleagues come up with values ​​that are comparable in size to meteorological causes. “Our calculations show that migratory locust swarms can reach a charge density that can exceed the density of electric storms and clouds,” the scientists wrote. In contrast, butterflies, which usually migrate only in very loose and much less dense flocks, have much less impact on atmospheric electricity.

“Our results indicate that large populations of insects were 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 alter the air around them. “This discovery has significant implications for many areas that are both physically and biologically relevant,” the team said. Because these electric fields generated by living organisms can affect the transport of dust, pollen or aerosols into the atmosphere. “There are many unexplored connections between biology and static electric fields, ranging in the spatial scale from soil microbes to pollinator interactions with plants to large swarms of insects,” Hunting says. There is still much to be researched in the dynamic interactions between atmospheric physics and biology.

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Source: Ellard Hunting (University of Bristol) et al., iScience, doi: 10.1016/j.isci.2022.105241