This familiar, strong-flying species is our largest white butterfly (2), and is often an unwelcome visitor to gardens because the caterpillars damage cabbages and other realated crops (2). Females are distinguished by two black spots and a black streak on the fore-wings (1). In both males and females, the undersides of the wings are yellowish with black flecking (1). The caterpillar grows up to 4 cm in length, and is generally pale green with black spots, with a yellow line along the back and one along each side (3).
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).
The caterpillars feed on wild or cultivated crucifers (members of the cabbage family), and prefer cultivated cabbages and Brussels-sprout (varieties of Brassica oleracea), as well as oil-seed rape (Brassica napi) (2). It is therefore usually seen close to farms and gardens (2).
A winter survival strategy characteristic of some mammals in which an animal's metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer. In insects, the correct term for hibernation is 'diapause', a temporary pause in development and growth. Any stage of the lifecycle (eggs, larvae, pupae or adults) may enter diapause, which is typically associated with winter.
Stage in an insect's development, when huge changes occur that reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis. The pupa is often covered by a silk cocoon.
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