The male of this species ([Plate VII], fig. 1) is readily to be distinguished from all other members of the genus by its pale glossy blue, but the female (fig. 2 of [Plate VII]) so closely resembles that of Bellargus that it is often a somewhat difficult matter to discriminate between them. The following, however, are a few points worthy of observation: The upper side of the female Corydon has the bases of the wings more or less sprinkled with the pale silky blue that characterises the male; and the black bars of the fringe are usually broader in Corydon than in Bellargus. The black-centred spots of the under side are also usually more conspicuous in the former species than in the latter.
The difficulty of identification is increased by the fact that both these butterflies frequent similar localities, and are often on the wing at the same time; but although Corydon is certainly a frequenter of chalky districts, yet it is often found plentifully in districts far removed from the chalk, notably at Arnside in Lancashire, and in Epping Forest.
The butterfly is out in June and July. The caterpillar is green, with two rows of short yellow streaks on the back, and a yellow stripe on each side. It feeds on the purple and Dutch clovers
(Trifolium pratense and T. repens), bird's-foot trefoil (Lotus corniculatus), horse-shoe vetch (Hippocrepis comosa), and lady's fingers (Anthyllis vulneraria).
The Holly Blue (Lycæna Argiolus)
While all the other Blues delight to sport on low flowery banks in the full blaze of the summer's sun, the Holly Blue prefers to flit among the branches of trees, often many feet from the ground. The larva feeds on the flowers of the holly (Ilex Aquifolium) in the spring, and on those of the ivy (Hedera Helix) late in the summer; also on the alder buckthorn (Rhamnus Frangula); and it is in localities where these grow that we may find this lovely Blue sporting among the branches, or resting on a leaf with its wings folded together, thus making itself conspicuous among the dark foliage by exposing the pale silvery blue of its under surface.
