A Brimstone butterfly in Portugal.
It's one of the longest lived butterflies, living up to thirteen months, although most of this time is spent in hibernation. As 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.
On the upper side the male is sulphur yellow and the female white with a greenish tinge.
Their wing shape is unique and is designed to act as camouflage while they rest and during hibernation.
There is a popular myth that it is this butterfly at the origin of the word butterfly, a corruption of butter-coloured fly.