The Butterflies of the British Isles

by Richard South

The egg is yellowish in colour, somewhat skittle-shaped, and very prettily ribbed and reticulated. On Plate [5] there are two figures of the egg from enlarged drawings by Herr Max Gillmer, to whom I am greatly indebted for the loan of them. In the figure on the right, the dark spot at the shoulder of the egg represents the head of the young caterpillar, and in that on the left is seen the caterpillar about to come out of the egg. The head is already out, and the jaws have left their mark on the egg-shell. Most caterpillars of the Whites, as well as those of other butterflies, devour their egg-shells.

The eggs are laid in batches of from six to over one hundred in each batch. They are placed on end, and on either side of a leaf, chiefly cabbage. Herr Gillmer writes that he watched a female depositing her eggs on a leaf of white cabbage in the hot sunshine, and found that she laid twenty-seven in about nine minutes. A previous observer had timed a female, and noted that she produced eggs at the rate of about four in the minute. Caterpillars hatch from the egg in about seven days in the summer. The caterpillar (Plate [5]) when full grown is green tinged with blue or grey above, and greenish beneath. There are numerous short whitish hairs arising from little warts on the back and sides; the lines are yellow. The caterpillars feed in July, and sometimes again in September and October, on all plants of the cabbage tribe, and also on tropæolum and mignonette. A number of these caterpillars may often be seen crowded together on a cabbage leaf, and they sometimes abound to such an extent that much loss is sustained by growers of this most useful vegetable. A peculiarity of these caterpillars is that even when not numerous, their presence is indicated by an evil smell that proceeds from them. The unpleasantness of the odour is greatly intensified if the caterpillars are trodden upon.

The chrysalis (Plate [5]) is of a grey colour, more or less spotted with black and streaked with yellow. It is often to be seen fixed horizontally under the copings of walls, the top bar of a fence, or a window-sill; but it sometimes affects the upright position when fastened in the angle formed by two pales. A position that affords some measure of protection from weather is generally selected.

Although this butterfly is almost annually to be seen, in greater or lesser numbers, throughout the country, it is occasionally scarce, either generally or in some parts of the British Islands. For example, during the past year (1905) it was abnormally plentiful in Ireland, but at the same time comparatively rare in England. It is a migratory species, and no doubt its abundance in any year in these islands is dependent on the arrival of a large number of immigrants. Possibly in some years none of the migrant butterflies reach our shores, and that it is largely to this failure the rarity of the species in such years is to be attributed. Caterpillars resulting from alien butterflies may absolutely swarm in the autumn of one year, but the eccentricities of an English winter may be too much for the vitality of such of them as escape their enemies, Apanteles glomeratus, and other so-called "ichneumons," and reach the chrysalis state. So, with immigration on the one hand and destructive agencies on the other, it may be understood how it comes about that the Large White is sometimes abundant and sometimes scarce.

This species seems to range over the whole of the British Islands, with the exception, perhaps, of the Shetlands. Abroad, it has been found in all parts of the Palæarctic Region, except the extreme north, and Eastern Asia.

The Small White (Pieris rapæ).

The Small White butterfly (Plate [11]) is, perhaps, more often in evidence then its larger kinsman just referred to. It also is a migrant, and although it never seems to be absent from these islands, in its proper season, its great increase in numbers in some years is almost certainly due to the arrival of immigrants.

The spring form of this butterfly, named metra by Stephens, who, together with others, considered it a good species, has the tips of the fore wings only slightly clouded with black; and the black spots near the centre of the wings are always more or less faint in the male. Sometimes the central spot and also the blackish clouding of the tip are entirely absent. The summer brood, on the other hand, has fairly blackish tips and distinct black spots—one in the male and three in the female, the lower one lying on the inner margin. Occasionally examples of this flight bear a strong resemblance to the Green-veined White, the next species. The wings are sometimes, chiefly in Ireland, of a creamy colour, more especially in the female, or, more rarely, of a yellowish tint. In North America, where this species was accidentally or intentionally introduced some years ago, bright yellow forms are not uncommon in some localities, and the variety is there known as novangliæ.