Small tortoiseshell butterfly caterpillars (Aglais urticae), living socially on a stinging nettle leaf (Urtica dioica). During the larval stage, the caterpillars group together, spinning a silken tent from behind which they feed on the host plant. They are fully grown by four weeks, measuring approximately 2 centimetres in length. The butterfly is common throughout much of the Palearctic region, from Europe to the Far East.