After a particularly devastating summer for flora and fauna, there may be something pointless in telling a butterfly story. But we are not going to deprive ourselves of good news, as tiny as the protagonists. It is very precisely azures of the wild thyme, a species of blue butterfly whose wingspan can reach 4 cm and which is widely threatened in our latitudes.
In the United Kingdom, the species was even declared extinct in 1979. It was without counting on the team of scientists who, four years later, tried to reintroduce it into several protected areas thanks to Swedish larvae. In 2021, the results are dazzling: the population of « Large Blue » – as they are called across the Channel – has reached levels not seen for 150 years. The news was announced in late August by the Royal Entomological Society.
“Incredibly Satisfying”
David Simcox, one of the researchers involved in this reintroduction in the 1980s, told the BBC in August how he was “incredibly satisfying” to see them prosper. And to remember: “I didn’t have a single gray hair on my head when I started. Now they are all grey. »
How to explain such a success? Scientists have first unraveled the mystery of the decline of wild thyme since the 19th century.e. They thus discovered that this butterfly depends on an ant to develop. When it emerges from the egg, the caterpillar secretes a chemical substance to attract ants which, mistaking it for one of their own, carry it to their anthill and take care of it during the winter, until the formation of the chrysalis and metamorphosis into a butterfly.
Virtuous circle for other species
An operation that caused the loss of the Large Blue. When the UK gradually abandoned grazing and hares were decimated, grass levels rose, cooling the temperature of the ground. This change in temperature led to the decline of the host ants, and with it, that of the butterflies.
The discovery enabled the British to adapt protected areas and recreate ecosystems conducive to the development of this species. Virtuous effect: other insects have begun to come back or have multiplied thanks to conservation measures. Bumblebees, beetles, bees – one of which had disappeared from the country for fifty years before the 2000s – or even eight other species of endangered butterflies.
Proof that the decline of species is not irreversible, once the means of their protection are implemented. Scientists are not claiming victory, however. In the eyes of David Simcox, “the biggest challenge ahead is to secure progress, despite global warming”.