Biology

Typically, two generations are produced each year (3). The first brood of adults emerges in spring and flies until April. A second, larger brood of adults appears in July (2), and in particularly warm years, a third brood may occasionally occur (2). The eggs are laid in batches, on leaves of the foodplants (2), hatching after around a week (3). In their early stages, the caterpillars live in groups (2), and can be extremely damaging, reducing the foodplant to a mere skeleton (3). They become solitary later on in life (2), and are very distasteful to birds because they consume mustard oils from their diet (2); their bright colouring advertises this fact, protecting the caterpillars from attack (3). Members of the broods produced later in the year hibernate through the winter as a white pupa (2) attached to walls, fences, tree trunks and occasionally the foodplant (3).