It is the yellow colour of the wings of the male Brimstone (the archaic name for sulphur) that gives Gonepteryx rhamni its common name; it has also been suggested that the origin of the word ‘butterfly’ refers to the butter-like colour of the Brimstone’s wings. The wing colouration has even been the subject of an entomological hoax. In 1702, the naturalist William Charlton claimed to have found a new species of butterfly which resembled the Brimstone, but had ‘black spots and blue moons on the lower wings’ – the description was accepted by eminent entomologists for the next ninety years until the original specimens were more closely examined and found that the spots had been painted on!
The breeding and egg-laying period, mid-April to early July, occurs in habitats supporting buckthorn, the leaves of which are the main food source for the larvae. When the adult is at rest amongst the foliage, the shape and pronounced veins of the closed wings closely resemble leaves. During winter, adult Brimstones migrate to woodlands to hibernate, preferring areas with holly, ivy and bramble where they are better camouflaged. Adults emerge from hibernation in April and range widely along roadside verges, hedgerows and woodland edges.
