Butterflies of
Britain & Europe
Green-veined White
Pieris napi
LINNAEUS, 1758
Family - PIERIDAE
subfamily -
PIERINAE
Tribe - PIERINI
introduction
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habitats |
lifecycle |
adult behaviour
Green-veined White
Pieris napi, 1st brood male,
Stansted Forest, Sussex
Introduction
This
is a widespread and common species occurring throughout Europe, temperate Asia,
and at high altitudes in the Atlas mountains of
north Africa. It also occurs in North America, where it is known as the Mustard
White.
When
seen in flight it can be confused with the Small White Pieris rapae, but while the
Green-veined White has a lazy flight, usually fairly close to the ground, the
Small White has a stronger and more directional flight pattern, and appears
brighter and more conspicuous.
It can
also be confused in flight with the female Orange tip Anthocharis cardamines, which flies in
very similar habitats. The differences between the two are immediately apparent once the butterfly
has settled - the Orange tip having a very distinctive mottled green and white
underside quite unlike that of the present species.
The
two broods of the Green-veined White differ slightly in appearance. The
underside hindwings of the spring brood have the edges of the veins heavily
peppered with grey. In summer brood adults this peppering is much reduced. In
both broods the ground colour of the underside hindwings is more yellowish in
the female. On the upperside females of both broods have 2 dark squarish spots
on each forewing. First brood males lack these spots entirely, but there is a
single spot present on males of the summer brood.
I have
sometimes come
across individuals that were very much smaller than average, for example at Noar
Hill, Hampshire, in August 2004, and again at Stockbridge Down on 14th July 2007 I found singletons
each no larger than a
Chalkhill Blue.
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Green-veined White
Pieris napi, 1st brood pair,
Hampshire |
Habitats
The Green-veined White is
found throughout Britain, with the exception of the Shetland Isles. It occurs in
damp sunny and sheltered situations such as woodland rides, glades, riverbanks,
ditches and dykes bordering hedgerows, and wet meadows.
Although it can sometimes
be seen flying in open habitats such as grassland and heaths, it usually
prefers to stay close to it's breeding sites.
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Green-veined White
Pieris napi, 2nd brood female,
Stockbridge Down, Hampshire, England |
Lifecycle
There are normally 2 generations
in Britain, emerging in May-June and in early August. The second brood is always
far more numerous than the first. There is occasionally a
partial third brood which emerges in late September. At high
altitudes and in the far north of Britain however there may be
just a single brood, emerging in June.
The straw-coloured eggs are
laid singly on the undersides of leaves of various crucifers,
including cuckoo flower
Cardamine pratensis, garlic mustard
Alliaria petiolata, hedge mustard
Sisymbrium officinale
and water
cress
Nasturtium officinale; more often
on tiny seedlings than on larger plants. The butterflies usually prefer to oviposit on plants growing in damp sunlit situations, often along the edges
of woodland ditches and paths.
The caterpillar feeds solitarily
during daylight, and is a dark slightly bluish green colour,
with yellow spiracles. It can be found in June and again in
August.
The offspring of spring adults normally produce pale green
pupae, which blend perfectly amongst living stems and leaves.
Those produced by the offspring of summer adults however are
destined to spend the winter in hibernation, attached to dry
woody stems, and are usually pale straw in colour. Nevertheless
this general rule of thumb is occasionally broken, and a small
percentage of each brood produce pupae of the "wrong" colour.
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Green-veined White
Pieris napi, 2nd brood male,
Hampshire, England |
Adult behaviour
Green-veined Whites, in common with their close relatives the
Small and Large Whites, are among the first butterflies to take
flight on cool or overcast days, often appearing an hour or more
before other species awaken. In such weather conditions they spend
long periods reflectance-basking, but take flight as soon as
the clouds thin and there is a hint of warmth.
In sunny weather
the butterflies make short but regular flights, pausing every few seconds to nectar at low growing
flowers. Spring nectar sources include bugle, dandelion, cuckoo flower and cranesbill,
while the summer brood favours knapweed, marjoram, thistles and hemp
agrimony.
In addition, males also commonly imbibe mineralised moisture from
the edges of puddles. The minerals obtained are required to
replace those lost during mating.
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Reflectance
basking : In hazy conditions many species of butterfly
bask with their
wings held slightly apart, so that the warmth of the
sunlight is reflected onto the dark thorax, enabling the
butterflies to gain energy rapidly. This habit is also
practiced by Small Whites, Large Whites, Orange tips, Small
Coppers, and most Blues. |
Freshly emerged females sit among grasses or low herbage to await discovery
by patrolling males. Mating takes place after a short chase,
and immediately after copulating the pair fly to settle on a bush
or on higher ground, with the male carrying the female in flight.
If disturbed the pair take readily to the wing and will often make
several short flights until they find a spot where they are out of
reach of predators. They remain paired for about an hour.
At Stansted Forest in May 2008,
I watched a Green-veined White
searching for places to lay her eggs. Every few seconds she would alight momentarily on a leaf, "tasting" it
using the olfactory sensors on her feet to check whether or not it
was the correct foodplant for her offspring. It was
surprising to find that she tested bracken, ivy and oak leaves,
all of which are very different in shape from the crucifers she needed to locate
for oviposition. This appears to indicate that in this species sight
plays little or no role in selecting plants for egg-laying.
The relative importance of the
visual, olfactory and tactile senses for oviposition behaviour
probably varies however from species to species.
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