Brimstone: That this butterfly is the origin of the word ‘butter-fly’ with its abundance and colour, flying early in the year, is a lovely story. Brimstones over-winter as adults in woodland and hedgerow places such as amongst ivy. They can appear at any time in January or February flying on warm sunny days but will inevitably return to hibernation. They emerge properly in late March and April and will wander widely in search of mates, and for the females, in search of purging buckthorn around Westbury and alder buckthorn in parts of the country with more acidic soils. The males are bright yellow and unmistakeable, while the females are a much paler greenish cream colour – resembling large whites in colour and size. However, once they settle, with wings always closed, the lack of black wingtips and the pointed shape of the wings make them easy to recognise. Having found a suitable buckthorn shrub, the female will flutter around until exactly the right places have been found and then lay one egg in each of them. These eggs hatch to produce a green caterpillar which can be found quite easily by looking closely at the leaves of a buckthorn bush. The pupa is formed on the underside of a leaf and has the appearance of a folded leaf. By the end of June the adults that flew in April and May will have died and during July and August the new generation of adults will have emerged from their pupae and will be feeding up on nectar from flowers, often purple or blue, such as knapweed and buddleia, before going into hibernation for the winter. There is just this one generation a year.
Photos Peter Bright