They are migratory. Starting in early spring, they journey from Africa to Europe to the United Kingdom and eventually the Arctic Circle. The journey is about 7,500 miles. They travel at up to 30 miles per hour.[1] Their caterpillars feed on many different plants. In the UK their caterpillars may feed on thistles.
The lifespan of a painted lady imago (adult) is only about 2/3 weeks. Its function is dispersal and reproduction. The caterpillar's job is eating and transforming itself into the adult form.
References
↑BBC News UK. Painted lady butterfly influx needs people to count them. [1]