PLATE 7.
[Apparatus for Preserving Larvæ]
The question of the migration of this and the following species is still very far from being satisfactorily settled. That we do get a swarm over from the Continent when conditions are favourable is a matter of common knowledge, but whether we have resident and permanent colonies of our own is still doubtful. In any case this year (1911) has been a Hyale year, and we give thanks. The ground colour of this butterfly is a pale primrose-yellow. There is a broad black border beginning at the tip of the fore-wing and continuing on to the hind-wing, where it gradually dies out at the bottom angle; placed on this band of black are a few yellow spots. There is also a black spot on the fore-wing, and a faint orange spot near the middle of the hind-wing. The under side is more of a yellow shade, and a line of brown spots runs round the outer margin of both wings. There is a silvery spot in the centre of the hind-wings, like a figure 8 bordered with pinkish brown, and in fine fresh specimens the fringe is of the latter colour. The female is a shade lighter in ground colour and also shows more black.
The caterpillar may be looked for in June and July on Clover and Lucerne; it is green, with yellow lines running along the back and sides. The chrysalis is green with a single yellow line.
The latter half of August and the first half of September cover the best period of its flight in this country; on the Continent there is a spring brood.
The Clouded Yellow (Colias Edusa), [Plate IV.], Fig. 1.—As with the last species, we have still much to learn of the habits of this fine butterfly. Some years it is plentiful, while in others hardly a specimen will be seen—and as for the caterpillars, we never hear of them being successfully searched for. The probability is that from a few spring visitors from the Continent we get a number of descendants in August, when a great many more arrive from across the Channel and mingle with them. The distribution of nearly all animals is regulated by the food-supply, the climate, or their enemies; yet none of these seem to satisfactorily account for the disappearance and reappearance of Edusa with us. It is a strong flying insect with a roving disposition, and on quite a few occasions it has been noted as far north as Arran and the Ayrshire coast, in Scotland. The brilliant orange and black wings make its identity unmistakable. Not so, however, with the light sulphur-coloured female variety, which very nearly approaches the typical female form of Hyale, but it may be distinguished by the broader black band on both fore- and hind-wings, and a heavy sprinkling of black scales near the base of the former, and all over the latter. The orange spot too, in the centre of the hind-wing is deeper, and, being on a darker ground, looks much brighter. There is no corresponding male variation.
The caterpillar is dark green, with a light line on each side, varied with yellow and orange touches. It feeds on various plants of the pea order—vetches, trefoils, clovers, etc. The chrysalis is brown spotted, and is striped with a yellow line. The butterfly appears with us during August and September.