The bright brimstone butterfly is a welcome sight in early spring
THE RICH LEMON-YELLOW OF A MALE brimstone butterfly is spectacular at any time – this is an insect that can nowadays be seen in the UK from February until November. But it seems especially fine in early spring sunshine, when the first freshly woken individuals are on the wing. The naturalist Michael McCarthy, one of the co-authors of The Consolation of Nature: Spring in the Time of Coronavirus, writes: “The brimstone is so bright it looks like a piece of sunlight that has become detached from the sun’s rays and freed to wander.” By contrast, the female brimstone is a subtle shade of greenish-yellow.
Emerging this early in the year means brimstone butterflies need some clever strategies to heat their thorax muscles, which power the wings, to the 35°C necessary for flight. They do this by seeking sheltered sun-traps, such as the south side of a hedgerow or grassy bank. But even that is not enough. So the butterflies perch and bask, angling their folded wings towards the sun. After basking, they can fly in an air temperature as low as 13°C.