This butterfly comes out first in May, and is met with from that time till August.
THE BRIMSTONE BUTTERFLY. (Gonepteryx Rhamni.)
([Plate III]. fig. 2.)
Though one of the commonest of our native butterflies, this, like numberless other very common things, is also one of the loveliest, both in the graceful outline of its wings, and in the lively hue that overspreads their surface; charms the more to be appreciated, as this insect is one of the few that do not wait for the full bloom of summer ere they condescend to make their appearance, but in the earliest, chill months of spring, and even in the dead winter season, the country rambler is sometimes gladdened by its gay flight; and in fact there is not one winter month that is not occasionally enlivened by this flying flower, when a day of unwonted mildness and sunshine tempts it from its winter retreat.
Until very recently it had always been stated by entomologists, that the Brimstone Butterfly was "double-brooded" (a term meaning that it went through two whole cycles of existence, from the egg to the perfect insect, in one year), one brood appearing in May, and the other in the autumn.
But it is now established, on very satisfactory evidence, that one brood only is produced, and that, the autumnal one. A considerable number of these survive the winter in some place of concealment, and coming out again in the spring form the so-called spring brood. Many of these hybernators are found to be in very fair condition in the spring, but in general they lack the perfect freshness and bloom of those taken in autumn; the wings of those I have taken at this period are often semi-transparent, from having lost feather, and frequently are spotted and discoloured, as if by mildew; a sign probably of their owners having wintered in damp lodgings.
Mr. Douglas states that they get very fat and full of honey before consigning themselves to their long winter's sleep; evidently an instinctive provision against the waste of substance that must of necessity accompany all, even the most sluggish vitality: in this respect following the same instinct that leads bears, and other hybernating animals, to fatten up to their utmost stretch before retiring for the season.