Adult small tortoiseshells (Aglais urticae) overwinter in window cracks and in the sheltered depths of sheds. On warm spring days they emerge as the first butterflies of spring to bask in the sun and drink nectar.
The males soon take over nettle stands and start attracting females to join them. The females lay their eggs on the nettles. The black-and-yellow caterpillars that hatch from the eggs feed on nettle leaves. The caterpillars are poisonous, so they are not eaten by birds. Small tortoiseshells produce one or two broods per year. The small tortoiseshell is one of the most common butterflies in Finland.