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.
Life cycle 
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.
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.
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. Like many other "White" butterflies, they hibernate as a pupa. It is also 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.
Like its close relative the Large White this is a strong flyer and the British population is increased by continental immigrants in most years. Adults are diurnal and fly throughout the day, except for early morning and evening. Although there is occasional activity during the later part of the night, it ceases as dawn breaks.
- RR Scott & RM Emberson (compilers) (1999). Handbook of New Zealand Insect Names. Entomological Society of New Zealand. ISBN 0-9597663-5-9.
- Scudder, SH (1887). "The introduction and spread of Pieris rapae in North America, 1860-1886". Memoirs of the Boston Society of Natural History 4 (3): 53–69.
- Agrawal, AA & NS Kurashige (2003). "A Role for Isothiocyanates in Plant Resistance Against the Specialist Herbivore Pieris rapae". Journal of Chemical Ecology 29 (6): 1403–1415. doi:10.1023/A:1024265420375.
- Fullard, James H. & Napoleone, Nadia (2001): Diel flight periodicity and the evolution of auditory defences in the Macrolepidoptera. Animal Behaviour 62(2): 349–368. doi:10.1006/anbe.2001.1753 PDF fulltext
Further reading 
- Asher, Jim et al.: The Millennium Atlas of Britain and Ireland. Oxford University Press.
- Evans, W.H. (1932): The Identification of Indian Butterflies (2nd Ed.). Bombay Natural History Society, Mumbai, India.
- "Pieris rapae". Integrated Taxonomic Information System. Retrieved 6 February 2006.
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