In Britain, one or more generations may be produced during a single year, depending on the climate (2). The female lays eggs singly on the upperside of leaves of the foodplants (3). The eggs hatch after around a week, and the caterpillars create a tent-like shelter of leaves spun together with silk, within which feeding takes place. They pupate inside these shelters, and the adults emerge after around two weeks (3). In 1997 it was first shown that adults are able to overwinter in Britain, although it is not known if adults are capable of breeding after overwintering (2). There is currently no evidence to suggest that this species migrates south at the end of the season (2). In some years, the migration of this species involves enormous numbers of individuals; in 1996, many millions of painted ladies arrived in Britain, and the event made the headlines at the time (2).