The eggs should be sought for in the month of May, or a little earlier or later, on the buds and young shoots of the two species of Buckthorn (Rhamnus Frangula and R. Catharticus). When examined with the microscope, these are found to be very pretty objects of conical form, with sculptured ribs on the sides.
The caterpillar that results from these, when it grows up, is of a fine green colour, shagreened over with black points, and shading off into a paler line along the side. Its shape is represented at [Plate I]. fig. 2. It is found on the young buckthorn foliage that forms its food.
The chrysalis is of the remarkable shape shown on [Plate I]. fig. 13,—green, marked with yellow. It remains in this state for about twenty days, when the perfect butterfly appears.
The general colour of the male Brimstone Butterfly is a clear, brilliant yellow, much like that of the Daffodil, its contemporary; and in the centre of each wing is a small spot of rich orange-colour. A very beautiful feature to be remarked in this butterfly is the silken mane, so to speak, composed of long hairs of silvery gloss and whiteness, which are arranged as if combed up from the sides of the thorax, so as to meet in a crested form over the top.
The female chiefly differs from the male in the ground colour of the wings, which are of a pale and very peculiar greenish white tint, rather more deeply tinged with yellow at the extremities of the wings.
As the male, from his colour, bears the name of "Brimstone," or "Sulphur," the complexion of his mate may be accurately compared to the tint of another
sulphureous preparation, called by druggists "milk of sulphur."
The only noticeable variation this butterfly is subject to in this country is in the size of the orange wing-spots, which are sometimes greatly enlarged.