This insect appears in July, and is common in many dry, sandy, or chalky spots in various parts of England, and also in a few localities in Scotland and Ireland. It has been reported as abundant at Darlington and in certain localities in Lancashire, but its head quarters are undoubtedly the chalk downs and dry gravelly banks of the southern counties.
The caterpillar feeds on the bird's-foot (Ornithopus perpusillus), and is full grown towards the end of June. Its colour is yellow or grey, with a brown dorsal stripe, a white line on each side, and pale oblique lines near the former. About the end of June it changes to a dull green chrysalis, with projecting wing cases.
The Brown Argus (Lycæna Astrarche)
Neither male nor female of this species exhibits any trace of blue. The upper surface, shown in fig. 13 of [Plate VI], is coloured with a warm brown, and all four wings have a row of orange spots near the hind margin. The fore wings have also a central black
spot. The under surface, drawn on the same plate (fig. 14), is bluish grey, with a border of orange spots on each hind margin as on the other side. There are also numerous black spots in light rings, the arrangement of which will be seen in the figure.
Some species of butterflies and moths are so variable in their colouring and markings that varieties have often been mistaken for distinct species; and, in other cases, distinct species are sometimes so similar in character that they are looked upon as identical.
A butterfly that closely resembles the normal Brown Argus in many points, and named Artaxerxes, has often been described as a distinct species, but is now, I believe, recognised by most entomologists as a constant variety of the present species.
It differs from the normal type in having a white instead of a black spot in the centre of the fore wings, and the border of orange spots is often very indistinct. On the under side, too, instead of black spots in white rings, it has white spots, with little or no trace of a black centre.
The ordinary Brown Argus is a southerner, and is particularly abundant on the chalk downs of the south coast and the Isle of Wight, but Artaxerxes is to be found only in Scotland and the north of England; and it is interesting to note that, between these northern and southern districts, intermediate varieties are to be met with.
Again, Astrarche is a double-brooded butterfly, appearing on the wing in May and August; while Artaxerxes is single brooded, flying at midsummer. This fact has lent support to the opinion that the two are distinct species; but it must be remembered that several insects that are single brooded in one country are double brooded in a warmer climate.