Butterflies of
Britain & Europe
Small White
Pieris rapae
LINNAEUS, 1758
Family - PIERIDAE
subfamily -
PIERINAE
Tribe - PIERINI
introduction
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habitats |
lifecycle |
adult behaviour
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Small White
Pieris rapae, 2nd brood female,
Noar Hill, Hampshire, England |
Introduction
The
Small White is one of the commonest and most widely distributed species in the
world ( the most widespread of all being the Painted Lady ). It occurs
throughout all of Europe, including the sub-arctic areas of Scandinavia, the
Outer Hebrides, all of the Mediterranean islands, the Azores, and the Canary
Isles.
Beyond Europe it occurs in north Africa, Tunisia, throughout the Middle East, and
eastward across temperate Asia to Japan. It was introduced to Quebec in 1860,
and to California in 1866. By 1881 it had spread across most of the eastern
United States, and is now a common species throughout all of temperate North
America, where it is known as the Cabbage White. During
the 20th century it was introduced to many more countries, including Bermuda,
Australia, New Zealand and Iceland.
In Britain it
can be confused in flight with the Large White Pieris
brassicae, which is marked almost identically. The latter however is
considerably larger, averaging 58mm in wingspan, while
rapae averages only 47mm. It can also be confused with the Green-veined White
Pieris napi,
but appears brighter, slightly larger, and has a more powerful and purposeful
flight than that species, usually flying in a constant direction.
In
Europe rapae can be mistaken for the Southern Small White P.mannii,
in which the black spots in the median area of the forewings are crescent-shaped
( they are squarish in rapae
); and with the Mountain Small White
P. ergane,
in which the greyish apical patch is squarish ( concave in rapae
).
Habitats
This is a strongly
migratory species which can be found in any British habitat with the exception
of the highest mountain peaks. However it is far commoner in the vicinity of
gardens, allotments and farmland where crucifers ( cabbage, sprouts etc ) are
grown.
It
is also common in late summer at flowery grassland sites adjoining cruciferous
crops, and along the south coast, as arriving migrants.
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Small White
Pieris rapae, 2nd brood female,
Stockbridge Down, Hampshire, England |
Lifecycle
In Britain there are normally 2
generations, emerging in May and August. In exceptionally warm
summers there may be a partial 3rd generation emerging in
October. Migrants can arrive at any time, but tend to peak in
April and July. Thus it is possible to see this species at any
time between early April and November.
The pale yellow, skittle-shaped
eggs are laid singly on the underside of the leaves of cabbages
and
sprouts
Brassica,
garden nasturtiums
Tropaeolum, and less commonly on charlock
Sinapis arvensis
or other
wild crucifers. Often several eggs will be laid on the same
plant, or even under the same leaf, but these are laid by
different females, or by successive visits by a single female.
The dull green,
slightly hairy caterpillars feed diurnally on the leaves of the
foodplants. On cabbages the young larvae bury deep into the
heart of the plants, inflicting serious damage to the
developing leaves. When older they feed openly, nibbling a mass
of irregularly shaped holes out of the leaves, but leaving the
midrib and tougher veins intact.
They
are a serious commercial pest of cabbage crops but
do less damage than the larvae of the Cabbage moth Mamestra
brassicae.
Small White larvae
are heavily predated by harvestmen and nocturnal beetles, and by
birds including sparrows, tits, warblers and thrushes. Also, in
common with most other caterpillars they are attacked by various
parasitoids, the main culprit in this case being the wasp
Apanteles rubecula.
The chrysalis has several colour
forms, ranging from pale green to a dirty brownish white, with
dark dots on the abdomen. It is attached either vertically or horizontally to fence-posts,
brick walls, or the underside of shed roofs, windowsills and other
sturdy materials.
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Small White
Pieris rapae, 2nd brood female,
Stockbridge Down, Hampshire, England |
Adult behaviour
Early in the day, or in overcast conditions, the butterflies bask
with their wings half-open, reflecting solar energy onto the
thorax and abdomen, which are covered with dark hair-like scales
that assist in rapid heat absorption. In sunny conditions they
usually keep their wings shut when resting or nectaring, but
copulated pairs usually rest with wings partly open.
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Small White
Pieris rapae, 2nd brood
copulating pair,
Hampshire, England |
Males patrol
around cabbages and other crucifers, waiting to intercept females.
When the sexes meet, the male flies up and down in front of the
female, enticing her to settle, and then settles beside her. He
then uses his outspread wings to force the female to lean to one
side, and bends his abdomen round to copulate with her.
Immediately after joining, the pair fly a short distance to settle
on the foliage of a nearby plant. If a male intercepts an
unresponsive female, she spreads her wings and raises her abdomen
as a rejection signal.
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Small
White
Pieris rapae, 2nd brood female,
Martin Down NNR, Hampshire, England |
The
butterflies often congregate in sheltered gardens to oviposit, or
to seek nectar at cultivated flowers, particularly favouring
buddleia. In the countryside they often gather to nectar at
patches of hemp agrimony, marjoram, thistles, knapweeds, yellow
rattle, or valerian.
They roost singly, usually on
the upper surface of the leaves of bushes or herbaceous plants,
even in rainy weather.
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