The induction of melanism in the lepidoptera and its subsequent inheritance

Abstract The question of melanism in the Lepidoptera is of paramount importance inasmuch as this is one of the few recognizable evolutionary changes which have occurred in Nature in recent times and, for the most part, before the eyes of the present generation. Moreover, the change is not slight. Wherever melanism arises we see large numbers of species in groups widely separated systematically, developing forms in which white, ochreous and similar ground colours are replaced by black and blackish browns. Once initiated in a species, this transformation is progressive and often exceedingly rapid: frequently the whole of the individuals of the affected species become melanic in an incredibly short period. For example, in 1898 the Geometrid moth, Ypsipetes (Larentia) trifasciata, was quite typical everywhere in North Durham, yet, in 1910, every specimen captured or bred from wild pupæ—and over four hundred were examined—in that district belonged to the black variety, nigerrima Harrison; and this is typical of many similar cases.