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What these researchers at the University of St. Louis, Missouri, found, by observing hundreds of thousands of these insects is that the warmer the climate, the more male dragonflies see their color lighten. VSThis is easily explained: heat accumulates more easily in the dark-colored wings of dragonflies and therefore the lightening would be a necessary adaptation to avoid overheating which could be fatal.
Why is it only for males? One of the explanations is that these dragonflies spend a lot of time in the sun, while the females prefer to take refuge in the shade. Note in passing that this color change can have an impact on the attraction exerted by these males to their congeners and therefore ultimately lead to reproduction difficulties.
In a 2014 study, published at the time in Nature, German and Danish researchers looked at nearly 500 species of European butterflies and dragonflies. Results of their work: statistically, the darkest species were more frequent in the regions further north, in Great Britain, Norway, Finland, where the temperatures are the lowest, while predominant in the south, in the climates the warmer as in Spain or Sicily, species covered with light colors. The link is therefore established: the more the mercury increases, the more the clothing becomes lighter. And above all, in this same study, these scientists demonstrated, by focusing on dragonflies, that the clearest species had gained territory over the years, the observations having been carried out between 1986 and 2006.
More clear species and a progression of them towards the north were observed while at the same time the average temperatures had increased during the period: « Global warming favors clear insects in Europe « , concluded the authors. And the corollary is that these animals are a marker of this change in our latitudes. The condition being, to observe it in the future, that these species do not completely disappear. In 2017, a study published in the journal PlosOne estimated that European insect populations had declined by almost 80% in less than 30 years.