In certain favourable years a partial third brood has occurred, but such specimens are often small in size.
The egg (Plate [8]) is at first pale greenish, but later on it turns yellowish, and this tint it retains until just before the caterpillar hatches out.
The caterpillar when full-grown has a brownish head and a green body; the latter is sprinkled with black and clothed with short blackish hairs emitted from pale warts. There is a yellowish line on the back, and a line formed of yellow spots on the side. It feeds on most plants of the cabbage tribe, and in flower gardens on mignonette and nasturtiums. It is often attacked by parasites, and especially by the Apanteles, referred to as destructive to caterpillars of the Large White.
The chrysalis may be of various tints, ranging from pale brown, through grey to greenish; the markings are black, but these are sometimes only faint. It is to be found in similar situations to those chosen by the caterpillar of the last species, but often under the lower rail of a fence or board of a wooden building. Where caterpillars have been feeding in a garden, they often enter greenhouses, among other places, to pupate; and where these structures are heated during the winter, the butterflies sometimes emerge quite early in the year. Distributed throughout the British Islands, except the Hebrides and Shetlands. It is common over the whole of Europe, and extends through Asia to China and Japan. In America, where it was introduced into the United States some forty-five years ago, it has now spread northwards into Canada, and also southwards.
The Green-veined White (Pieris napi).
This butterfly is not often seen away from its favourite haunts in the country; these are woods, especially the sunny sides, leafy lanes, and even marsh land. As in the case of the two Whites previously noticed, there are always two broods in the year. The first flight of the butterflies is in May and June, occasionally as early as April in a forward season. These specimens have the veins tinged with grey and rather distinct, but are not so strongly marked with black as those belonging to the second flight, which occurs in late July and throughout August. This seasonal variation, as it is called, is also most clearly exhibited on the under side. In the May and June butterfly (Plate [13,] left side) the veins below are greenish-grey, and those of the hind wings are broadly bordered also with this colour. In the bulk of the July and August specimens (Plate [13,] right side) only the nervures are shaded with greenish-grey, and the nervules are only faintly, or not at all, marked with this colour.
Now and then a specimen of the first brood may assume the characters properly belonging to the specimens of the second brood; and, on the other hand, a butterfly of the second brood may closely resemble one of the first brood. As a rule, however, the seasonal differences referred to are fairly constant. By rearing this species from the egg it has been ascertained that part (sometimes the smaller) of a brood from eggs laid in June attains the butterfly stage the same year, and the other part remains in the chrysalis until the following spring, the butterflies in each set being of the form proper to the time of emergence.
Pl. 8.