After a decade’s worth of effort, an international team of researchers has for the first time been able to track the swarms of migratory insects that soar above the skies of southern England each year, according to a new study published online Friday by the journal Science.
What they found was that approximately 3.5 trillion bugs and butterflies migrate annual above the region, and that together they comprise 3,200 tons of biomass – seven times greater than the mass of songbirds that travel from the UK to Africa each year, and equal to some 20,000 flying reindeer, scientists from the University of Exeter and Rothamsted Research reported.
According to BBC News, the researchers counted the swarms of insects using a combination of vertical radar and balloon-mounted insect nets. They calculated the numbers of insects that flew at altitudes of 150 and 1,200 meters, both during the day and at night, for a total of 10 years.
“Insect bodies are rich in nutrients and the importance of these movements is underappreciated,” co-author Dr. Jason Chapman from the Centre for Ecology and Conservation at the University of Exeter’s Cornwall-based Penryn Campus explained in a statement. “If the densities observed over southern UK are extrapolated to the airspace above all continental landmasses, high-altitude insect migration represents the most important annual animal movement in ecosystems on land.”
Findings reveal the ‘complex’ mechanisms used by bugs and butterflies
The majority of the creatures were small bugs such as cereal crop aphids, flies and midges, but the scientists also tracked larger insects like hoverflies, ladybugs, moths and butterflies, the UK news outlet added. While their path of travel was not fully monitored, the scientists believe that many of the insects had been travelling across the English Channel and the North Sea.
Using radar sites in southern England to monitor the insects’ movements, the researchers found large seasonal differences in the migratory patterns of the creatures, with large numbers heading northward during the spring and towards the south during the autumn. They also found seasonal variations from year-to-year, but noted that the overall net northward spring movements of larger insects was almost exactly the same as the net southward movements during the fall.
The new study is the first to examine daytime insect migration, the researchers said, and one of its more surprising discoveries was that even though smaller insects took off regardless of wind direction, medium-sized and larger ones appeared to carefully measure the wind direction before deciding whether or not to begin their voyage on a particular day or night.
The discovery “signifies that the insects have a compass mechanism in order to know which is north and south” and “the capability to then fly up… assess the direction of the wind and relate it to the compass direction and make a decision on whether to fly or not,” Dr. Campbell told BBC News. “That’s a quite complex set of things and many, many species are doing this.”
“Animal migration, especially in insects, is a very complex behaviour which takes millions of year to evolve and is very sensitive to climatic condition,” added co-author Dr. Ka S Lim, of the Radar Entomology Unit of Rothamsted Research’s AgroEcology Department. “Global climatic change could cause decline of many species, but equally other highly adaptable species thrive and become agricultural crop pests.”
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