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 { 70} 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.
In a well-marked variety, common in the south of Europe, Madeira, &c., this enlargement reaches a great development, nearly the whole of the _upper_ wings being suffused with a deep orange, though in all other respects the insect does not differ from our common form. This beautiful variety has been described as a different species under the name of _Gonepteryx Cleopatra_; but M. Boisduval has proved that they are identical, by rearing both the ordinary _Rhamni_ and the _Cleopatra_ from the same batch of eggs.
The female _Cleopatra_ does not differ materially from _Rhamni_. I look on this variety as very interesting, as a probable instance of the direct effect of increased warmth of climate in intensifying colour.[9]
Plentiful as this butterfly is in all the southern counties, and extending in more or less abundance as { 71} far northwards as the lake district, it there becomes scarce; and I can find no instance of its having occurred in Scotland.
Of course, its prevalence in any district is naturally regulated by the abundance of its food-plants, the buckthorns.
Gardens, fields, and lanes are equally the resort of this favourite insect; and there the newly-hatched specimens are to be found on the wing from August to October.
THE CLOUDED YELLOW, OR CLOUDED SAFFRON. (_Colias Edusa._)
This richly-coloured and nimble-winged fly is ever the darling of the collector. None make a finer show in the cabinet, and few tempt pursuit more strongly than does this golden beauty when on the wing.
For many years past, and up to quite a recent period, the appearance of this butterfly in any abundance was a phenomenon only occurring at uncertain periods, separated by intervals of several years. In one season, perhaps, hardly a solitary specimen would be seen, and in the very next, a swarm of them would spread over the southern counties, delighting the fly-catcher and puzzling the naturalist to find a sufficient reason for { 72} this sudden burst of insect-life. Whether the eggs lay dormant for years, till hatched under peculiarly favourable conditions; or whether every now and then a few individuals were tempted to cross the Channel from the Continent by some attraction unknown to us, or were, _nolens_, _volens_, blown hither by the wind, and then deposited eggs which produced the next year's troop of butterflies; or, lastly, whether an agency was at work here, of whose nature we are entirely ignorant,--all these are questions that still remain to be answered. There is, I believe, no foundation for the opinion sometimes held by entomologists, that this species prevails at _regular_ periods, such as once in four, or once in seven years. In fact, for the last two or three years its permanent residence and appearance among us seems to be established, while, at the same time, its northward range has been greatly extended, a considerable number having been taken even _in Scotland_--its existence in that country having been previously quite unheard of.