The Small White (Pieris rapae) is a small- to medium-sized butterfly species of the Yellows-and-Whites family Pieridae. It is also known as the Small Cabbage White and in New Zealand, simply as White Butterfly. The names "Cabbage Butterfly" and "Cabbage White" can also refer to the Large White. It is widespread and populations are found across Europe, North Africa, Asia, and Great Britain.
It has also been accidentally introduced to North America, Australia and New Zealand where it causes damage to cultivated cabbages and other mustard family crops. The caterpillar stage alone is responsible for crop damage because of which it is referred to as the Imported Cabbageworm. In appearance it looks like a smaller version of the Large White (Pieris brassicae).
The upperside is creamy white with black tips to the forewings. Females also have two black spots in the center of the forewings. Its underwings are yellowish with black speckles. It is sometimes mistaken for a moth due to its plain-looking appearance. The wingspan of adults is roughly 32-47 mm (1.25-2 in). The species has a natural range across Europe, Asia and North Africa. It spread across the Atlantic into Canada and the United States beginning somewhere around 1860.
It spread to Hawaii by 1898, and Australia in 1929 around Melbourne and spreading across to Perth by 1943. The nominate subspecies P. r. rapae is found in Europe while the Asian populations are placed in the subspecies P. r. crucivora. Other subspecies include atomaria, eumorpha, leucosoma, mauretanica, napi, novangliae, and orientalis. 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.
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Its caterpillars can be a pest on cultivated cabbages, kale, radish, broccoli, and horseradish but it will readily lay eggs on wild members of the cabbage family such as Charlock (Sinapis arvensis) and Hedge mustard (Sisybrium officinale). The eggs are laid singularly on foodplant leaves. It has been suggested that isothiocyanate compounds in the family Brassicaceae may have been evolved to reduce herbivory by caterpillars of the Small White.