HONG KONG BUTTERFLIES
SEASONAL VARIATION
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In warm climates butterflies often run continuous broods at intervals of about two months. Even in England certain species, the Whites and Vanessidae, for instance, have more than one emergence during the year. The summer brood of the former is differentiated from the spring brood in that the spots are black instead of grey. The Common Blue (Polyommatus icarus) is two-brooded, but there is no difference in the marking, though the August brood is smaller than that in May. The Vanessas, Large and Small Tortoiseshell, Painted Lady and Common Red Admiral, and the rare visitor, the Camberwell Beauty, show no variation.
In Hong Kong, a large number of species have distinct dry and wet season forms, the change taking place at the turn of the monsoon in October and May. The general tendency is for the underside, which is displayed when the insect is at rest, to become less ornate in the winter months. When the leaves are on the trees, the tropical sun in summer produces a dappled effect of light and shade in the woods. Many butterflies have numerous white pupillated ocelli, which tend to break up the surface pattern on the underside to produce a protective camouflage. In the winter, the sun's rays are less obstructed, and the insects rest on the ground among the fallen leaves. The "eyes" disappear, and the ground colouring blends with the carpet of dried vegetation. One of the Satyridae, Mycalesis mineus, has a submarginal border of eight full-sized ocelli at the height of summer, and these are gradually reduced in size and number in successive broods during the autumn. In winter, the underside of the butterfly is entirely obsolete, blending perfectly with the dead leaves on which it rests. The process is reversed in the spring, each brood being more conspicuously provided with eyes than the last.
The Precis family, known as the "Pansy" butterflies, of which there are six species in Hong Kong, not only lose their underside ocelli in the dry season but considerably modify their whole outline. The wings are much more rounded in the wet season, whilst in the dry season, the tornus of the fore wing comes to an exaggerated point, whilst the inner angle of the hind wing is almost a tail.
The Pieridae, among which the "Whites" are found, show great seasonal variation. The underside, in both sexes, is almost plain