As one of the best-known insect groups in the world, butterflies are an extremely valuable marker of the health of invertebrates, and more broadly of biodiversity. The fifth edition of the report by the British NGO Butterfly Conservation, published in early February, draws an alarming conclusion regarding their status in the United Kingdom: In less than 50 years, they have disappeared from almost half of the places where they once flew. Between 1976 and 2019, the distribution of butterflies in the UK fell by 42% on average. The overall decline in butterfly abundance was 6%.
Richard Fox, a member of Butterfly Conservation and lead author of the study, said, “These figures are not a surprise. We have known for a long time that butterflies are declining significantly. But I still hope that this report will come as a shock, especially to policymakers, who have the means to act in response to these losses.”
The British, pioneers in citizen science, have been observing and above all documenting the state of their nature for decades. Since 1976, for example, volunteers on regarding 3,000 sites have been walking the same route every week, from April to September, counting the number of butterflies. And through another program, citizens can report species observed throughout the year, from any location in the UK. From this immense amount of information – 23 million items of data were used for the latest report – scientists can determine trends in both abundance and distribution.
The 2022 edition, which covers 58 species, shows that there are twice as many losers as winners among butterflies: 61% of species have declined in either distribution or abundance (or both), while only 32% have seen one of these two curves rise.
‘All the numbers are negative’
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By far the most affected are the “specialist” butterflies, i.e. those with specific ecological needs and who depend on a particular habitat. Species living in flowering meadows, heaths and wooded clearings declined by 27% and lost up to two-thirds (68%) of their range. The decline was somewhat less severe for “generalists,” which can breed in agricultural and urban environments, although they still declined by 17% and lost 8% of their range.
The average decrease in abundance of 6% since 1976 masks great disparities, with some species having increased significantly. The 3,000 sites where butterflies are counted are also overwhelmingly located in nature reserves, which may bias the results. “The most common species are clearly [the most talked regarding]but all the figures are negative, which is very alarming. And we see the same trends in France and northern Europe,” said Xavier Houard, head of the research and conservation division at the French nature protection group OPIE, which did not contribute to the report.
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