They are one of the world’s best-known groups of insects. The butterflies of the United Kingdom are, as such, an extremely valuable indicator of the state of health of invertebrates, and more broadly of biodiversity. However, the fifth edition of the report by the British NGO Butterfly Conservation, published in early February, draws an alarming conclusion: in less than fifty years, they have disappeared from almost half of the places where they were present. Between 1976 and 2019, butterflies in the UK have indeed lost, on average, 42% of their range and decreased by 6% in abundance.
“These numbers are not a surprise, we have known for a long time that butterflies are declining significantlyreacts Richard Fox, member of Butterfly Conservation and lead author of the study. But despite everything, I hope that this report will cause a shock, especially among politicians, who have the means to act in the face of these losses. »
Pioneers of participatory science programs, the British have been observing but above all documenting the state of their nature for decades. Since 1976, for example, volunteers have traveled each week, from April to September, the same route during which they count the number of butterflies, on approximately 3,000 sites. In parallel, another scheme allows citizens to report species sighted all year round and anywhere in the UK. From this huge amount of information – 23 million records 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, either in distribution or in abundance (or both), so that only 32% saw one of these two curves increase.
“All numbers are negative”
By far the most affected are the “specialist” butterflies, that is to say those with specific ecological needs and dependent on a particular habitat. Species living in flower meadows, moors and wooded glades have thus declined by 27% and lost up to two-thirds (68%) of their range. The fall was a little less steep for the “generalists”, which can reproduce in agricultural and urban environments, even if they nevertheless decreased by 17% and lost 8% of their range.
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