The Brimstone (Gonepteryx Rhamni)
This butterfly (Plate 26) has the tips of the fore wings sharply pointed, and there is a rather acute angle about the middle of the outer margin of the hind wings. The colour of the male is bright sulphur yellow, with a central orange spot on each wing, that on the hind wings usually the largest; there is also a rusty dot at the outer end of the upper veins and along the front margin of the fore wings towards the tip. The female is greenish yellow, and is marked similarly to the male. In both sexes the horns (antennæ) are reddish, and the long silky hair on the thorax is a noticeable character. It is probably this insect to which the name “butter-coloured fly,” contracted into butterfly, was first given; anyway, it is the only species to which the name applies so well.
The egg. If the under sides of the leaves of buckthorn (Rhamnus catharticus) or of the berry-bearing alder (R. frangula) are examined in May or June, the eggs of this butterfly may be found thereon. They are often placed on a rib of the leaf, but sometimes they are laid as shown in the illustration (Plate 25). At first the colour is pale greenish and rather glossy, but it soon changes to yellowish, and later on, when the caterpillar has formed inside, to a dull purplish-grey.
The caterpillar when full grown is green, merging into bluish-green on the sides, thickly powdered with shining black specks. There is a pale line on each side below the spiracles. It feeds in June and July on both kinds of buckthorn, and will generally be found resting along the main rib of a leaf.
The chrysalis is bluish-green in colour and of a curious shape. The sharp yellowish and brown beak-like projection in front and raised brownish bases of the wing-covers, together with the humped thorax, somewhat resemble a bird’s head when seen from the front. Then, again, the enlarged wing-cases, which are rather greener than the other parts, in conjunction with the general outline, give a very good imitation of a curled leaf.
The butterfly is very constant as regards colour and marking, but occasionally the fore wings may be more or less suffused with orange, and in this respect assumes the coloration of the South European species known as G. cleopatra. The attempt has been made to establish the last-named butterfly in Ireland, but the experiment seems to have been only partially successful. Sometimes female specimens are found to have splashes of the male colour on their wings. Occasionally their colour is intermediate between their own proper tint and that of the male, and more rarely the wings on one side may be yellow, as in the male, while those on the other side are greenish, as in the female. Such specimens are termed gynandrous examples, and sometimes hermaphrodites. The latter, however, is not correct.
An unusual variation of the butterfly is shown on Plate 27. This has large oval pale brownish-orange marks on the under side of the wings. It was taken in the New Forest.
The Brimstone butterfly enjoys a longer existence in the perfect state than any of the other British species, with the exception, perhaps, of the Tortoiseshells and their allies. It leaves the chrysalis at the end of July or beginning of August, and is usually quite common during the latter month. After this it takes up its winter quarters, from which, however, it may be tempted to come out whenever the day is sufficiently warm and sunny for it to indulge in a few hours’ flight. The fine condition of some of the specimens that are seen in May or June has suggested the possibility of such specimens having remained in the chrysalis during the winter, but it is not at all probable that they do so. It may be seen any sunny day from March, or even February, to June in almost every English and Welsh county where its food-plant grows, and locally in Ireland. The best time to take specimens is in the autumn, when they are often to be seen in numbers flying along the rides in or on the outskirts of woods, and also in clover fields.
Distributed over the whole of temperate Europe, and extending through Asia to the far east and to North Africa.
The thirty butterflies now to be considered belong to the Nymphalidæ, which has a larger membership than any other family of butterflies. It is divided into several sub-families, but only four of these concern us; these are Apaturinæ (1 species), Nymphalinæ (17 species), Danainæ (1 species), and Satyrinæ (11 species). The next butterfly is our only representative of Apaturinæ.