On a wing and a prayer | 27 June 2019

In 1979, despite the best efforts of scientists for more than a century, a butterfly called the British Large Blue became extinct. There is widespread concern about the more recent decline in butterfly populations, but the American ecologist Nick Haddad writes that the collective weight of the known populations of the five rarest butterflies he discusses in his sobering book is just ‘three pounds five ounces — as much as one panda’s paw’. The special importance of butterflies, he argues, is that they provide lessons about the decline and management of other threatened species.

The fate of the British Large Blue shows how difficult it can be to conserve a creature that requires very specific conditions in order to survive: not only wild thyme, its main food source, but also colonies of a particular species of ant on which the caterpillars preyed and which itself favoured steep, south-facing slopes, and rabbits to keep the grasses to less than 2.1