The Induction of Melanism in the Lepidoptera, and its Evolutionary Significance

Abstract

IN recent vears no more remarkable evolutionary phenomenon has been observed than the development and progress of melanism amongst British native Lepidoptera. Species after species of moth with pale ground colour has given rise to forms so heavily pigmented that they appear in some cases to be dark grey and in others perfectly black. Further, the course of events has not ended with the mere appearance of these melanie forms; in affected species a state of equilibrium has only been attained in the areas concerned when the whole of their representatives has assumed the melanie guise. On Tyneside, for example, twenty-five years ago the species Boarmia repandata (the Mottled Beauty) was quite typical; now every specimen captured is black. Moreover, the advance of this progressive melanism is not stayed locally, for new species fall under its influence every year, the latest to yield being Phigalia pedaria (the Pale Brindled Beauty) and Tephrosia bistortata (the Engrailed).