Genus PIERIS, Schrank, 1801 
THE LARGE WHITE 
Pieris brassicae (Linn., 1758). 
(Plate XXVI, facing page 301) 
Although the Large White occurs annually throughout 
Britain in varying numbers and usually abundantly, owing 
to its migratory habits it is occasionally scarce over the 
greater part of the country, or even over the whole of the 
British Isles. Vast swarms have often been observed at sea 
on migration and arriving on our coasts, sometimes in such 
multitudes as to resemble snowstorms. Vessels at sea have 
at times been covered by them settling on the rigging and 
decks. They have also frequently been seen to alight with 
expanded wings upon the surface of the sea, from which they 
rise apparently with as much ease as from the ground. 
It is due to such great invasions that this butterfly, in 
certain seasons, suddenly appears in profusion in different 
parts of the country, while in other years it is rare. These 
visitations occur both in spring and after midsummer, usually 
about the end of May, or the end of July or in August. But 
during the years when it is abundant, one of its most formidable 
natural enemies, a minute ichneumon fly (Apantcles glomeratus ), 
which is parasitical on the larva, swarms to such a degree 
that comparatively very few of the butterfly caterpillars 
escape ; consequently their numbers are so reduced that the 
following year the Large White may be comparatively rare. 
Haunts. The Large White may be met with almost every¬ 
where from the seashore to the middle of large towns. Its 
favourite haunts are gardens, lanes, meadows and fields, 
especially those of Beans, Clover and Lucerne. Beans are 
particularly attractive when in bloom ; both the nectar of 
the flowers and the honey-dew which usually covers the 
leaves, exuded by the Bean aphis, provide the butterfly with 
abundant nourishment. 
This butterfly usually selects light-coloured or variegated 
foliage and white-flowered plants to rest upon for the night. 
I have often observed it carefully selecting suitable plants 
for the purpose. 
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