THE BRIMSTONE 
337 
one in spring and the other in autumn. But only one brood 
occurs in the year, either in July or August. 
Hibernation. The Brimstone apparently very often enters 
into hibernation shortly after emergence, and usually selects 
evergreens for its winter retreat, chiefly Ivy and Holly, clinging 
to the under side of a leaf. From its remarkable resemblance 
in both form and colouring to the surrounding foliage of its 
hibernaculum, it is practically invisible. When an Ivy leaf 
is chosen, the resemblance between the butterfly and the 
leaf is so perfect that it is one of the most complete examples 
of protective resemblance occurring in nature. 
This butterfly pairs in the spring, usually at the end of 
April or beginning of May. When the sexes meet on the wing, 
they go through a prolonged dalliance flight in the sunshine, 
and finally settle to pair. 
Egg Laying. The Brimstone generally deposits its eggs 
towards the end of May or during the first half of June and 
sometimes as late as the beginning of July. The eggs are laid 
singly on the under side of the leaves of both species of Buck¬ 
thorn (Rhamnus cartharticus and R. frangula) and on no 
other plant. The egg stage lasts about ten days. 
Egg. The egg is laid singly, standing erect, on the under 
surface of a young leaf, but occasionally on the stem of a 
young shoot close to the leaf stalk. It measures 1-30 mm. 
high, and somewhat resembles in shape a champagne bottle. 
As a rule there are ten longitudinal keels running from the 
summit to the base, and about forty-five very fine transverse 
ribs. The colour wnen first laid is a whitish-blue-green, re¬ 
maining the same for three days, then gradually changing to 
citrine-yellow and later on a deeper yellow. Finally, before 
hatching, it becomes drab-grey. 
Larva. Directly after hatching from the egg the little 
larva is 170 mm. long. It rests in a straight position, lying 
along one of the ribs, and in feeding perforates the leaf. 
It becomes fully grown after the fourth moult; it then 
measures from 31-80 mm. to 34 mm. The colouring of the 
upper surface is glaucous-green, darkest on the back, with a 
slightly darker median line. The colour gradually blends into 
bluish to the white spiracular stripe, which is rather dilated 
along the lower edge. The under surface, including the legs 
B.B. 
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