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An astounding number of insects migrate overhead

American Association for the Advancement of Science

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IMAGE: The helium-filled tethered-balloon and aerial net set-up was used to sample the high-flying small insects. This material relates to a paper that appeared in the Dec. 23, 2016, issue of... view more

Credit: Ian Woiwod

A decade of monitoring aerial insect migration reveals that trillions of individuals travel above us each year. Migration contributes greatly to seasonal exchanges of biomass and nutrients across the Earth's surface; however, even though insect migration surpasses all other aerial migratory phenomena in terms of sheer abundance, it remains largely unquantified. Here, Gao Hu and colleagues set up vertical-looking entomological radars (VLRs) in the southern U.K. to track the migration of flying insects, gathering data for nearly a decade. The results reveal that an annual mean of 3.37 trillion insects migrated high above the region, comprising 3,200 tons of biomass. The majority of migration, more than 70% in terms of biomass, occurred during daytime. The authors report that migration intensity was greatest on warm days, with moderate to high surface heat flux and low surface wind speeds. Analysis of wind trends and migration revealed that large insects exploit seasonally beneficial tailwinds to get from A to B. As well, surface and high-altitude daytime wind directions were strongly correlated; thus the authors propose that surface wind direction provides a reliable cue regarding the suitability of winds for daytime travelers at take-off, but not for nocturnal migrants, which must use other methods for assessing high-altitude wind direction. Lastly, over the 10-year course of the study, the overall northward movements of larger insects in the spring was found to cancel out southern migration in the fall; however, on an annual basis, the net flux could be up to 200 tons greater in either direction, the authors report.

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