For many in the United States, the soundtrack of a lazy summer evening is the drone of insects filling the air. But how does one translate that languorous buzz to the cumulative insect air traffic across the entire U.S.?
Weather radar. That’s how.
Typically, flying insects are accounted for at local scales through sampling in natural areas (if you’re thinking butterfly nets, you’re not too far off). But those numbers don’t extrapolate to entire countries or continents. Researchers from the Swiss Federal Research Institute, the University of Oklahoma, and the Massachusetts Institute of Technology have devised an estimation method that takes advantage of weather radar data already gathered by large radar networks. And the insect numbers they’ve tallied are wild.
Based on data from 140 NOAA weather radars across the continental U.S., about 100 trillion insects fly over the lower 48 on a typical summer day, according to the new findings published in Global Change Biology. Collectively, this mass of insects comprises millions of tons of biomass that sustain birds and other insectivores.
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While individual insect species aren’t identifiable in the compiled data, the radar information is valuable in monitoring overall insect abundance. The new methodology allows for analysis of trends, such as long-term flighted insect population and behavioral responses to climate change.
The researchers constructed a time series of continental U.S. flying insect abundances from 2012 to 2021 and found the overall abundance to be remarkably stable over those years. Fluctuations were regional, with winged insect density rising in some areas and falling in others, in association with winter temperatures. Where winters got warmer over that period, density of these insects decreased, and where they got cooler, density increased. The higher the latitude, the more dramatic the winter-warming effect. In their paper, the study authors explain that warming may disrupt the cold-induced dormancies that allow some insect species to conserve energy during lean winter months.
So, even though the climate effects might so far balance out at a continental scale, temperature fluctuations appear tied to insect abundance at a regional scale. “It is therefore important to combine radar data with other data sources—local surveys, citizen science, and so on,” says Swiss Research Institute biologist Elske Tielens in a statement. It’s also likely that steep insect declines preceded the inception of NOAA radar data, i.e., pre-1990s, says Teilens.
Going forward, the weather radar approach provides a baseline against which researchers can measure future changes in flying insect populations across the continental U.S. The approach can also be used in other parts of the world that are undergoing intense anthropogenic changes, but where ground-based insect counts are not as common or as feasible as the radar snapshots—to help track the number of wings behind all that buzz. 
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Lead image: Tunatura / Shutterstock
