Brimstone Gonepteryx rhamni
The pupa is a remarkable and lovely shape. The butterflies hatch easily. Difficult to hibernate, but you can keep them for a while with fresh nectar flowers, and then release to hibernate and hopefully breed in your area.
Resulting pupae produce butterflies this summer. They hibernate amongst ivy (when closed, the wings resemble ivy leaf undersides). Because they are difficult to hibernate in captivity release the butterflies in summer sunshine, you may help to perpetuate the species to re-appear as one of the earliest and most prominent butterflies to be seen each spring in your area.