The Small White (Pieris rapae) is a small- to medium-sized butterfly species of the Yellows-and-Whites family Pieridae. It is also commonly known as the Small Cabbage White and in New Zealand simply as white butterfly.
The Small White is widespread across Europe, North Africa and Asia and has also been accidentally introduced to North America, Australia and New Zealand where they have become pests on cultivated cabbages and other mustard family crops. In Britain, it has two flight periods, April–May and July–August, but is continuously-brooded in North America, being one of the first butterflies to emerge from the chrysalis in spring, flying until hard freeze in the fall.
Traditionally known in the United States as the "Imported Cabbage Worm", now more commonly the "Cabbage White", the caterpillars are green and well camouflaged. Caterpillars rest on the undersides of the leaves, thus making them less visible to predators. Unlike the Large White, they are not distasteful to predators like birds. It is one of the most cold-hardy of the non-hibernating butterflies, occasionally seen emerging during mid-winter mild spells in cities as far north as Washington D.C.
Source: en.wikipedia.org/wiki/Small_White - 09.10.2010