Butterflies of
Britain & Europe
Large White
Pieris brassicae
LINNAEUS, 1758
Family - PIERIDAE
subfamily -
PIERINAE
Tribe - PIERINI
introduction
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habitats |
lifecycle |
adult behaviour
Large White
Pieris brassicae, 2nd brood
male, Noar Hill, Hampshire
Introduction
The Large White,
often inaccurately referred to as the Cabbage White, is
distributed across the whole of Europe including the
Mediterranean islands and the sub-arctic areas of Scandinavia.
It also occurs in Morocco, Algeria, Tunisia, Libya, and across
temperate Asia to the Himalaya mountains. It does not occur
naturally beyond these regions, but was accidentally introduced
to Chile. A similar species, Pieris cheiranthi
is endemic to the Canary Isles ( but is facing extinction ).
Female Large Whites have a pair of
prominent black spots in the median area of the forewings, but
these are absent in the male. The spots are visible on the
underside forewings of both sexes.
Both sexes can be confused with
the Small White
Pieris rapae
but in that species the dark markings are fainter - greyish
rather than black - and the wingspan averages only 48mm as
compared to the 63mm male and 70mm female of brassicae.
The species is widely reared in
science laboratories and used as a subject for study by
geneticists, biochemists and physiologists.
Migration
As
with many other Pierines, the Large White is strongly migratory and can appear in
virtually any habitat. In
Britain it is commonly seen in coastal areas during migratory influxes, and
often occurs in high numbers on flowery chalk grassland habitats in mid summer.
Occasionally a mass
migration takes place. On 31st July 2009 e.g. I witnessed a gathering of
in excess of 250 migrants at Noar Hill in Hampshire. This site is an isolated hill with
a great profusion of nectar sources and consequently a major refuelling stop
for migrants. At
times I could stand in one spot and see 50 or more within a
10 metre radius. The insects were very active, often flying in migratory
"strings" of 7 or 8 at a time, pausing now and then to nectar avidly at
marjoram, thistles and knapweed.
On
9th August that year I witnessed an even greater concentration of migrants at
Broughton Down, also in Hampshire. At least 700 Large Whites were present, many
of which remained in the vicinity until the end of the month,
e.g. when I revisited on 24th August in cool overcast weather there were still
between 250-300 basking on herbage within a 50m x 30m patch of
hillside.
The above numbers may sound impressive, but are nothing in comparison to the massive swarms
which occurred in times past. There are several fascinating accounts of Large
White migrations in C.B.Williams
book "Insect Migration", including this quote from Turpyn:
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"In 1508, the 23rd
year of Henry the 7th, the 9th of July being relyke Sonday, there was sene at
Calleys ( Calais, France ) an in-numerable swarme of whit buttarflyes cominge out of the
north-este and flyinge south-eastwards, so thicke as flakes of snowe, that men
beinge a shutynge in St Petars
fields without the towne of Calleys could not see the towne at foure of the
clock in the aftarnone, they flew so highe and so thicke". |
A
more recent record tells of a swarm that descended on a small island in the
Norfolk Broads :
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"In August 1911 Professor Oliver was visiting a small island
of about 2 acres
on Sutton Broad, Norfolk. As he approached he saw the whole
island covered with fluttering white butterflies, all of
them were caught on the sticky leaves of the Insectivorous
plant, the Sundew. Each small plant had captured 4 to 7
butterflies; mostly they were still alive when Professor
Oliver saw them. Several counts gave an average of about six
million butterflies caught in this gigantic trap". |
Habitats
Large Whites breed primarily in gardens, allotments and farmland where
they
often become
a pest on cultivated Brassica ( cabbage,
sprouts etc ).
Because of its migratory lifestyle
the butterfly is not restricted to these breeding sites, and appears commonly in
a gamut of habitats including woodland rides, flowery hillsides, meadows,
heaths and parks.
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Large White
Pieris brassicae, 2nd brood
male, Noar Hill, Hampshire |
Lifecycle
There are usually 2 broods of this species in Britain, emerging in May and
August; and sometimes a third brood emerging in October. The resident population is supplemented by migrants from Europe,
which often arrive in large numbers during the spring and autumn. Thus it is
possible to see adults of this species at any time from February to November.
Numbers fluctuate greatly from year to year, largely in response to climatic
conditions and cycles of parasitism, but partly influenced by the number of
migrants arriving in the spring. These originate in Sweden and northern Europe,
and gradually spread south and west, so migrants can arrive in Britain either
from Scandinavia or from France.
The
deep yellow skittle-shaped eggs are laid in batches of up to 100, on the
underside of leaves of cabbage, sprout, nasturtium, sea kale and other wild or
cultivated Cruciferae. The butterflies have been
shown to be able to
detect the presence of existing egg batches laid by other females, and will
not normally lay additional batches on the same plant. The eggs hatch after
about 10 days.
The
caterpillars feed communally, reducing the leaves to a skeleton of veins before moving on
to adjacent plants. They are a major pest, causing vast damage to
Brassica crops and cabbages grown in gardens and
allotments. They are conspicuously marked in black and yellow aposematic
colours, and sequester mustard oils from the foodplants, which render them
distasteful to avian predators. The mustard oils contain sulphur compounds,
which bestow the larvae and their droppings with an acrid odour.
About 80 percent of larvae are killed by parasitoid wasps Apanteles glomeratus,
which inject their eggs into them when they are quite small.
The eggs hatch
inside them, and the wasp grubs slowly devour the caterpillar's flesh. When the
grubs are fully grown they eat the caterpillar's vital organs and kill it. They
then break out through it's skin leaving it to die, surrounded by a cluster of
up to 80 tiny yellow fluffy wasp cocoons. The wasps hatch from the cocoons the
next spring, and fly in search of more caterpillars to parasitise.
The
pupa is formed in a vertical or horizontal position, attached by the
cremaster and a silken girdle to walls, fences or tree trunks some distance away
from the foodplant. Initially it is a dirty greyish green colour, covered with
small black and yellow spots, but the ground colour soon fades to a pale dirty
buff hue.
Many pupae, when freshly formed and soft, are attacked by
another parasitoid wasp, Pteromalus puparum,
which completes it's entire lifecycle within the chrysalis. A single Large White
pupa can produce a dozen or more of these tiny wasps, which are very beautiful
creatures, metallic emerald green in colour.
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Large White
Pieris brassicae, 2nd brood
male, Noar Hill, Hampshire |
Adult behaviour
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.
The adult butterflies
are highly mobile, covering vast distances and exploring all
available habitats in search of their larval foodplants and nectar
sources. They have a powerful
undulating flight which is undeterred by obstacles such as trees,
bushes and buildings, over which they commonly fly.
Once they arrive at a flowery site they tend to stay for several
days. In sunny weather they make short but regular flights,
pausing briefly every few seconds to nectar at low growing
flowers. Spring nectar sources include dandelion, bugle and wood
spurge, while the summer brood butterflies favour thistles,
knapweeds, marjoram, buddleia, scabious and hemp
agrimony.
When a male encounters
a gravid ( previously copulated ) female, she dives instantly into
grasses or herbage, snaps her wings shut, and remains motionless,
relying on her underside camouflage to hide from the male. He is
usually able to find her however by detecting her pheromones and
tries quite aggressively to force himself on her. At first she
responds by swaying slowly from side to side. This is quickly
followed by her partly opening her wings, which prevents the male
from making contact from the side. She then raises her abdomen at
a steep angle ( possibly emitting a chemical deterrent at
the same time ) to signal her refusal to mate, and the male then
flies off.
I have often found
copulated pairs at rest on low foliage or on robust flowers. In
July 2009 I had the unusual experience of watching the precise
moment at which copulation ended. I had been watching a mated pair
for a couple of minutes, from a distance of several feet away when
the pair parted. The male relaxed his anal claspers to release the
female, which then dropped almost to the ground before flying
away. The male remained in position for a while, then opened his
wings to bask before flying in the opposite direction.
In overcast or hazy conditions the
butterflies often bask on low foliage or amongst grasses, holding
their wings half open to deflect solar energy onto the dark
thorax.
The butterflies roost overnight in
bushes or high in trees.
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