On our walk through the woods we saw this butterfly, always the first of the season. The adults (the butterfly) overwinters under loose bark of trees, so when it warms up (it was +12) they will emerge, and if it cools down again, seek shelter once more. They can often be found nectaring on tree sap.

In the UK, this is called the Camberwell Beauty. From what I understand, these butterflies are mostly found in Europe and migrate to Britain in spring/summer. I don't know if they have adopted the same overwintering habits as the North American ones have.