ol6 REPORTS ON THE STATE OF SCIENCE, 



Melanism in Yorlishire Lepidoptera. By G. T. Porriti, F.L.S. 

 [Ordered by the General Committee to be printed in extenso.'] 



I HAVE undertaken to introduce the subject of melanism in Yorkshire 

 Lepidoptera to the members of tlie Zoological Section, chiefly with a view 

 to eliciting discussion on a subject which I feel, notwithstanding all 

 that has been said and written upon it, we really know very little about. 

 I may say at the outset, that I have no definite theory as to the cause 

 of melanism to advance myself, and probably I have very little that is new 

 to bring forward respecting it. But as Yorkshire, with parts of Lan- 

 cashire, is essentially the home of this phenomenon, it was thought that a 

 meeting of the British Association in the county ought not to be allowed 

 to go by without some reference to it. 



I need not explain to a zoological audience that by the term melanism 

 as applied to Lepidoptera we mean an increase or substitution of black on 

 the wings or body, or on both, at the expense of some other colour. 

 Melanochroism, as you know, is the substitution or darkening of some 

 colour other than black ; but I liave no intention of more than alluding 

 to that, because we see comparatively little of it in Yorkshire ; beyond the 

 fact that species generally have a greater depth of colour than the same 

 species elsewhere; but, £o far as we know to the contrary, that has 

 always been so. Some allusion will be made to leucochroism, which is 

 the tendency in directly the opposite direction to melanism, because, 

 although they are few, we liave some marked examples, which mutt 

 necessarily bo taken into account in a discussion on melanism. 



It is now five-and- twenty or more years since West Yorkihire 

 lepidopteristg began to notice that various species of whicli a black, or 

 nearly black, specimen had occasionally been taken were producing these 

 dark forms in increasing numbers, some of them rather rapidly. Years 

 before then, indeed, a quite black form of the old familiar pepper 

 moth, Amphi/dasifi betularia, was well known ; but although it had 

 developed within the memory of the present generation of entomologists, 

 it remained for years practically our only representative of real melanism. 

 Even williin my own collecting experience it was regarded as good 

 fortune to find one among the ordinary black-and-white ' peppered ' form. 

 Now, it is not only the dominant form, but in the South- West Riding 

 area has practically altogether ousted the original pale form. In tlie 

 Haddersfield district I have seen only one pale specimen during, the past 

 nine or ten years, and a typical specimen is now quite a rarity compared 

 with what the black form was even in my collecting experience. More 

 recently the black form has spread all over Yorkshire and many parts of 

 Lancashire, and is even occasionally taken in the South of England. It 

 is most curious, too, that in this species the black form appears to have 

 developed suddenly ; i e., it was not a gradual darkening, as no inter- 

 mediates were noticed in a wild state. True, our old ordinary form was 

 rather more densely peppered, and so was darker, than was the southern 

 type, and it often lacked the distinct zigzag black line which, to my mind, 

 gives to many of the South of England specimens so much prettier an 

 appearance ; yet the fact remains that the specimens taken at large were, 

 and still are, either black or, comparatively speaking, quite pale. I do 



