Once in Yorkshire, Painted Ladies are fast breeders and can move from egg to new butterfly in around four weeks minimum, although due to weather conditions this far north, the timescale is often longer.
The mating behaviour of the species is rarely seen in the wild. It is presumed that as with other Vanessid butterflies this takes place in trees or shrubs under cover of darkness but there is still a lot to learn about this relatively common species.
The light green eggs turn grey before hatching after seven to ten days. Larvae are black and hairy, covered in tiny cream dots, with almost continuous yellow lines along the sides. They feed in silk webs on leaf undersides and later make tents of folded leaves using silk threads. Larvae need warmth and sunshine for success and lots of rain or cloud can be a disaster.
Larvae pupate after developing through five instars in seven days or more, depending on the conditions. The pupae hang from leaves and come in two attractive forms, one brown with a golden sheen, the other silver-grey. The butterfly emerges after about two weeks, though longer in cooler weather.
The species is thought to be continuously brooded in North Africa where huge numbers can build up during our winter months and at some point this triggers a northward movement, occasionally even in winter, and arrivals from January onwards can happen along the south coast of England and occasionally reach further north, though not recorded for Yorkshire. Early arrivals probably die due to the cold.
Painted Lady migrations occur in various ways from broad fronts l00 miles across, to bands of a few metres wide but many miles long, and linear streams, with butterflies passing one behind the other for hours at a time.