Brimstone Butterfly

The butterfly that names butterflies

There is a popular but contested theory that the brimstone gave butterflies their name — the Old English buttorfleoge (butter-fly) may refer to the male’s butter-yellow colour, which is unlike any other British species. Whether or not the etymology holds, the male brimstone is one of the most instantly recognisable British butterflies: a vivid lemon-yellow with a small orange spot on each wing.

Hibernation and the long adult life

The brimstone is unusual in spending the winter as an adult, roosting among ivy and holly leaves where its leaf-shaped wings — complete with realistic midrib and veins — provide extraordinary camouflage. Adults emerge from September onwards after breeding, build fat reserves through autumn nectar, then enter hibernation. When temperatures rise in late winter, they are among the first butterflies on the wing — sometimes as early as January in mild years.

Buckthorn dependence

The larvae feed exclusively on buckthorn and alder buckthorn. This restriction means brimstones are found wherever these shrubs grow — woodland edges, hedgerows, chalk scrub, and calcareous grassland. The female’s pale colouring blends with buckthorn leaves when she rests; eggs are laid singly on young buckthorn shoots. Conservation of brimstone populations depends on maintaining buckthorn in hedgerows and woodland edge habitats.

Sexual dimorphism

Male and female brimstones look so different they were historically considered separate species. Males are the vivid sulphur-yellow; females are such a pale greenish-white that they can be mistaken for large whites. Both sexes share the distinctive wing shape — angular with pointed tips — that helps them blend among leaves when roosting.