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
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.
The environs of London, especially on the south side, have been abundantly visited by this charming insect; but its tastes have a decidedly maritime tendency, and we find it has a marked preference for the South Coast; abounding, again, more especially towards the eastern end. Its favourite resorts are clover and lucerne fields, though dry flowery meadows, open downs, and the sides of railway-banks are also the scenes of its lively flight—for Edusa has indeed a lively flight, and his pursuer has need of the "seven-league boots," with the hand of
Mercury, to insure success in the fair open race, if that can be called a fair race at all, between a heavy biped, struggling and perspiring about a slippery hill-side, such as Edusa loves,—and a winged spirit of air, to whom up-hill and down-hill seem all one.
In truth, the best way to get Edusa is to watch and mark him down on a flower, then creep cautiously up till within range, raise the net quietly, and strike rapidly downwards over the insect, who usually darts upward when struck at; and, in nine cases out of ten, Edusa will be fluttering under the net. It is not the most heroic style of sport, this, but it fills the boxes admirably.
The caterpillar is of a deep green colour, having on each side a white line, marked with yellow and orange. It may be sought for in June and July, on various plants of the leguminous order, which form its food, such as None-such Trefoil (Medicago lupulina), Lucerne (M. Sativa), and Clover.
The chrysalis is in shape between that of the Brimstone, and Cabbage butterfly, green with a yellow stripe, and rust-coloured dots.
The butterfly seldom is seen on the wing till July, but August is its great season; and it lingers with us till late in autumn.
I remember the pleasure with which, on a chill, stormy day in October, I watched the sports of a pair who were my sole companions while sketching, in a remote, rocky nook of the South Welsh coast. Very
battered and weather-worn were the pretty creatures, but still retaining much of the golden bloom of their summer dress.