Pieris brassicae

Pieris brassicae is the large white, or cabbage white butterfly. Its caterpillars feed on the leaves of different kinds of cabbage. The imagines (butterflies) have a wingspan of about . 
The cabbage white is a common butterfly that occurs from North Africa up to Fennoscandia. There are two to three generations a year, usually Spring to Autumn. 
The butterfly has been classified as a pest because, of course, its caterpillars eat cabbages. Sometimes, "Cotesia glomerata", a parasitic wasp, is used as a means of biological pest control.
The butterflies are distasteful to birds because of the mustard-oil glucosides the larvae eat. This oil has a distinctive pungent taste. It is in all plants in the mustard family, Brassicaceae (for example, cabbage, cauliflower, turnip, radish, horseradish, or wasabi).
Their white colour is easily seen, and probably acts as a warning sign.