38 THE BUTTERFLIES OF THE BRITISH ISLES. 



similar situations to those chosen by the caterpillar of the last 

 species, but often under the lower rail of a fence or board ot 

 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 



