They are one of the most famous groups of insects in the world. British butterflies are therefore extremely valuable indicators of the state of invertebrate health, and the state of biodiversity more broadly. However, the fifth edition of the report by British NGO Butterfly Conservation, released in early February, draws a shocking conclusion: In less than 50 years, they have disappeared from almost half of the places they once existed. 1976 to In 2019, butterflies in the UK did lose an average of 42% of their range and 6% in numbers.
“These numbers are not surprising, we’ve known for a long time that butterfly populations are in huge declineResponse from Richard Fox, a member of Butterfly Conservation and lead author of the study. But nonetheless, I hope this report will cause shock, especially among politicians who can afford to act in the face of these losses. »
As pioneers in participatory science programmes, the British have been observing, but most importantly documenting, its natural state for decades. For example, since 1976, from April to September, volunteers have traveled to about 3,000 sites each week, along the same routes they used to count butterflies. Meanwhile, another scheme allows citizens to report species seen anywhere in the UK throughout the year. From this vast amount of information—23 million records were used in the latest report—scientists can identify trends in abundance and distribution.
The 2022 edition, covering 58 species, showed twice as many losers among butterflies as winners: 61 percent of species had declined in distribution or numbers (or both), so only 32 percent of butterflies saw both. One curve in species increases.
“all numbers are negative”
By far the most affected are “professional” butterflies, that is to say those with specific ecological needs and dependent on specific habitats. Species living in flowery meadows, swamps and wooded glades consequently declined by 27 percent and lost as much as two-thirds (68 percent) of their range. For “generalists,” who can reproduce in both agricultural and urban environments, the decline was smaller, although they still lost 17 percent and lost 8 percent of their range.
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