Genus COLIAS, Fabricius , 1807 
THE PALE CLOUDED YELLOW 
Colias hyale (Linn., 1758). 
(Plate XXIX, facing page 324) 
This beautiful butterfly is a native of the Mediterranean 
regions, its true home appears to be the Riviera and north 
Africa, whence it migrates annually to central and western 
Europe, and its migrations occasionally reach this country 
in the months of May and June. Abroad it is found throughout 
the greater part of the Palaearctic Region. 
The erratic appearance of this species in England greatly 
puzzled the older authors, who were ignorant of the migratory 
habits of this and other immigrants ; consequently various 
theories were attributed to account for their appearance in 
certain years. During a period of over a century, the Pale 
Clouded Yellow has occurred in more or less abundance in 
the following years: 1821, 1S28, 1835, 1842, 1857, 1868, 
1875, 1892, 1900 and 1901. Since the latter date, there has 
been no year when it has been at all common ; several occurred 
in 1911, and others in 1921, but only in a few isolated places. 
Therefore, for over thirty years, this butterfly has been more 
or less rare over the whole of Britain. In 1842 it occurred 
abundantly all over the southern half of England, and reached 
as far north as York, the greatest numbers were in Kent and 
Sussex. In 1868 it was in greater profusion than ever known 
in this country, it swarmed in the Lucerne and Clover fields 
in the south-eastern counties. 
Time of Appearance. During the years when this butterfly 
has been abundant, the immigrants have been observed 
first in May or June, generally solitary specimens, scattered 
over the south and south-eastern districts. These then lay 
their eggs, and should the weather continue favourable, the 
larvae reach maturity and pupate, resulting in an abundance 
of the butterflies in the following August and September. 
Should the summer weather be cold and wet, the larvae 
perish. The butterflies of the August and September emer¬ 
gence in turn deposit their eggs, but the larvae from these 
are destined to destruction during late autumn, as the cold 
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