This summer has been a good one for this the largest of our butterflies. It's a real stunner - easily recognised by its scarlet and black livery and very powerful flight. This next bit is from the Hamlyn Guide to Butterflies of the British Isles. The egg is laid singly on the upper surface of small young leaves of Stinging Nettles or Hop. The caterpillar feeds on nettle leaves and lives hidden in a tent of one or several leaves, folded over and fastened together by silk. This is quite easy to find in July and early September. When fully grown (35mm) it is plump, spiny and very variable in colour; anything from dark, light or olive-brown, with tiny white speckles. There is a broad band of yellow along each side, often broken into patches.