302 



MELANISM IN LEPIDOPTERA.* 



G. T. PORKITT, F.L.S., IM:.S. 



Melanism, as applied to lepidoptera, is an increase or substitu- 

 tion of black on the \vini;-s or body, or on both, at the expense 

 of some other colour. The phenomenon has increased with 

 extraordinary rapidity in South-west \'orkshire and parts of 

 Lancashire, and also occurs in a lesser degree in many other 

 parts of the United Kingdom. In some species the changes 

 have been sudden, i.e., not a gradual progression from pale 

 to black, for instance the cases of Ampliydasis betiilariu, 

 Odotitopcni bideulafa, etc. But in most cases the change has 

 been gradual, though rapid. Over thirty species are melanic in 

 Yorkshire, the great majority of which have apparently become 

 so during the collecting experience of many present-day lepidop- 

 terists. In addition, there are also at the present time a con- 

 siderable number of other species, of which specimens so much 

 darker than the typical forms are so frequently taken, as to 

 indicate that they too are being influenced towards the same 

 end. The species in which Melanism was first noticed was 

 Aniphydnsis be/iilaria, and for many years it seemed to be the 

 only representative. But about twenty-five years ag"o Melanism 

 was noticed in several others, and since then additions to the 

 species have constantly been made. He detailed the progression 

 of the Melanism in Pligalia pilosaria, Tcphrosia biunditlan'u, 

 Hybernia proge nimaria, Diurnea fagel/u, Boanuia repandatd, 

 Arctia mendica, Polia chi, Odontopera bidciiiafa, Larciifid Dutllis- 

 frigan'a, Vcniisia canibricaria, Agrotis agdlJiiiui, Acroiiycta 

 me?iyau/hidis, and others. These have all apparentl}" become 

 black, or largely black, in recent years, and many of them in 

 some districts promised at no distant date to altogether oust 

 the old ordinary pale forms. One melanic form, the variety 

 varleyata of Abraxas grossiilariala, has md increased in num- 

 bers. Known more than forty }ears ago, it is to-day as rare as 

 it was then, although its hereditary tendency is so strong that 

 a brood raised this year from a pair of moths from wild lar\ le 

 were all of the extreme form, not a single example showing any 

 tendency to revert to the pale ordinary form or to any otiicr 



* Abstivicl of |);i|)cr rejicl to Si'clion 1) (Zoolo>;y ) of tin; Mci'liiij;- of (hi- 

 Hritisli Association, \'ork. The ])api'r ilsclf will bf printed in cxtciiso in tin- 

 Report of the Hrilisli Association. 



Naturalist, 



