A study confirms the alarming decline of this group of insects among the best studied in the world, which constitutes a precious indicator of the state of biodiversity.
by perrine mouterde
They are one of the best -known insect groups in the world. The butterflies of the United Kingdom are, as such, an extremely precious indicator of the state of health of invertebrates, and more broadly of biodiversity. Now the fifth edition of the report ‘British NGO Butterfly Conservation , published in early February, draws up an alarming observation: in less than fifty years, they disappeared by almost half of the places where they were present. Between 1976 and 2019, butterflies in the United Kingdom have indeed lost, on average, 42 % of their distribution area and reduced by 6 % in abundance.
“These figures are not a surprise, we have long known that butterflies decline significantly, reacts Richard Fox, member of Butterfly Conservation and main author of the study. But I hope this report will cause a shock , especially among political leaders, who have the means to act in the face of these losses. “
Pioneers of participatory science programs, the British observe but above all have been documenting the state of their nature for decades. Since 1976, for example, volunteers travel every week, from April to September, the same journey during which they have the number of butterflies, on around 3,000 sites. In parallel, another program allows citizens to report the species observed all year round and any place in the United Kingdom. From this huge mass of information – 23 million data was used for the latest report – scientists can determine trends both in terms of abundance and distribution.
The 2022 edition, which relates to 58 species, shows that there are twice as many losers as winners among the butterflies: 61 % of the species have declined, either in distribution or in abundance (or both ), while only 32 % saw one of these two curves increase.
“All figures are negative”
The most affected, by far, are “specialist” butterflies, that is to say those with specific ecological needs dependent on a particular habitat. The species living in flowery meadows, moors and wooded clearings have thus declined by 27 % and lost to two thirds (68 %) of their distribution area. The fall was a little less strong for “generalists”, who can reproduce in agricultural and urban areas, even if they have still decreased by 17 % and lost 8 % of their distribution area.
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