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Insect swarms charge the atmosphere with static electricity

Lightning during thunderstorms reminds us of the charged nature of earth’s atmosphere. However, static electricity is present in the air at all times, even during fair weather and away from thunderstorms. Electric fields in the atmosphere influence the movements of biologically relevant ions (e.g., nitrate, sulfate, radon) as well as dust particles. They are also known to facilitate animal dispersal and navigation. However, their origin has usually been thought to be abiotic and to involve local atmospheric electrical processes such as cloud electrification, lightning initiation, precipitation, aerosol charging, and radioactivity. 

A new study, published in the journal iScience, contends that living organisms can also have an impact on atmospheric electricity and may even help us to understand hither-to unexplained spatio-temporal variations in the lower atmosphere’s electrical fields. In particular, the researchers focus on flying insects that form swarms and undertake mass movements, such as locusts, honeybees, and migratory species of butterflies. 

“We always looked at how physics influenced biology, but at some point, we realized that biology might also be influencing physics,” said study first author Ellard Hunting, a biologist at the University of Bristol. “We’re interested in how different organisms use the static electric fields that are virtually everywhere in the environment.”

Insects such as honeybees gain a positive charge due to friction with air molecules as they fly along. This is a well-known phenomenon and has been proposed as a mechanism that helps pollen stick to a bee’s body as it forages from flower to flower. Given that bees form dense swarms at times of the year when they are looking for new locations to set up home, the researchers set out to measure the changes in electric field associated with the movement of these swarms.

The experts found that, as a swarm flew over their electric field monitor, there was a density dependent change in atmospheric electric charge of around 100Vm-1. The denser the swarm, the greater the increase in electric field force around ground level. This evidence suggests that a honeybee swarm contains enough charge to affect the atmospheric potential gradient, and that this source of electricity can represent an appreciable perturbing influence on the local electrical environment.

“How insect swarms influence atmospheric electricity depends on their density and size,” explained study co-author Liam O’Reilly, a biologist at the University of Bristol. “We also calculated the influence of locusts on atmospheric electricity, as locusts swarm on biblical scales, sizing 460 square miles with 80 million locusts in less than a square mile; their influence is likely much greater than honeybees.”

The researchers measured the electrical charge on individual desert locusts Schistocerca gregaria (805 + 295 Picocoulombs) and multiplied this by published estimates of swarm numbers to determine the possible effect of swarming locusts on local atmospheric electric fields.

The results revealed that locust swarms have the potential to alter their local electrical environment to an extent that is comparable with meteorological events such as thunderstorms. Butterflies, on the other hand, were found to have far less of an effect on electric fields due to their tendency to move around at much lower densities. 

“We only recently discovered that biology and static electric fields are intimately linked and that there are many unsuspected links that can exist over different spatial scales, ranging from microbes in the soil and plant-pollinator interactions to insect swarms and perhaps the global electric circuit,” said Hunting.

“Interdisciplinarity is valuable here – electric charge can seem like it lives solely in physics, but it is important to know how aware the whole natural world is of electricity in the atmosphere,” explained study co-author Giles Harrison, an atmospheric physicist from the University of Reading.

“As atmospheric space charge enhances the aggregation and movement of aerial particles, it is conceivable that insect-derived space charges will also contribute to spatial changes in aerial particles,” wrote the researchers. “For example, it could be speculated that insect-driven charged particle collection and transport could contribute to long-range transport of desert dust, providing alternative explanations for the transport of large particles, which cannot be explained by physical processes alone.”

By Alison Bosman, Staff Writer

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