The Brimstone has spread in recent years, mainly in northern England. When this butterfly roosts among foliage, the angular shape and the strong veining of their wings closely resembles leaves.
There is a view that the word 'butterfly' originates from the yellow colour of male Brimstones. The wings of the female are very pale green, almost white, males have yellow-green underwings and yellow upperwings.
It is widely distributed across the southern half of the United Kingdom, and has been steadily increasing its range in the north of England but is limited by the distribution of its larval food plants and is quite possibly close to its maximum possible distribution now unless their food plants' range also increases. In Ireland it has a much more localised distribution.
The Brimstone Butterfly is one of the longest lived butterflies, living up to thirteen months, although most of this time is spent in hibernation. It is often the first butterfly to be seen in the spring, sometimes as early as January when hibernating adults are awoken on a sunny day.
The eggs are laid singly on the leaves of either Common Buckthorn or Alder Buckthorn – the only two food plants – and females will wander far and wide in search for these particular shrubs. The larvae and Pupae are both green and very well camouflaged making them difficult to find in the wild. Upon emerging from the pupae, Brimstone butterflies spend the summer feeding on nectar to build up energy reserves for the winter and by the end of August they are already beginning their long sleep. They seek out evergreen scrub, a favourite being dense, old ivy growth. There is only one brood a year.