The brimstone is common throughout the New Forest and the rest of Hampshire. It is widespread and common in England, less common in Wales and Ireland and mostly absent from Scotland.
Brimstones can be seen in almost any habitat as they wander widely in search of mates and food. They lay their eggs on alder buckthorn trees in the National Park, which prefer damper areas, and they are quite fussy about exactly which tree they choose. They prefer trees in sunny positions, sheltered from the wind.
Being a yellow, or butter-coloured, fly, it is often thought that this species gave rise to the name ‘butterfly’. Unusually, brimstones spend the winter as an adult staying hidden in the shelter of ivy clumps and holly trees.
Brimstones can be seen just about anywhere in the National Park from April through to September, but they are most often seen in woodlands and areas with some trees. If you spend a sunny day in April, May or June in a New Forest woodland you will almost certainly see some brimstones.