MosLEY : On Causes peoducixg Variety in Lepidopteea. 55 



All kinds of animals found within the arctic circle have a tendency 

 to whiteness or uniformity of tint. In insects, look at many of the 

 arctic species of the genus CoUas ; as compared Tvith the more 

 southern ones the tints are more sombre and more unifomily diffused 

 over the wings — Nastes Boothii, &c. ; and though the dark Pobjodon, 

 or the dark Occulta or 'Daplark from Scotland, may be darker than 

 the same species from the south of England, yet the tint is more 

 uniform, and may serve as much for a protection in the peat bogs as 

 the whiteness of the ptarmigan or snow bunting does on the mountain 

 top. But it is curious, nevertheless, that a grt-at propurtiou of 

 varieties are darker — and sometimes considerably darker — than the 

 type. Look, for instance, at the black variety of Betularia ; and the 

 dark form of Biundularia in Delamere Forest. It is strange, too, 

 that at a certain place in Durham, many of the larvae of Grosm- 

 lariata are black, or very nearly so. I am not aware that this is the 

 case in any other part of England, and I can at present only suppose 

 that this is brought about by some process of natural selection, some 

 enemy having taken a fancy to the larvse of Gromdariu.ta in this par- 

 ticular district, and the blackness serving as a protection among the 

 black stems of the currant-bushes ; and this view seems the more 

 probable from the fact that the images in no way differ from the 

 ordinary form, which might not have been the case if the variation 

 had been due to meteorological or chemical causes. 



It is said {Ent. x., 132) that dry and withered food has a tendency 

 to produce small dark specimens, and that A. betularia or A. grossu- 

 lariata^ when fed in this manner, becomes black in a few generations . 

 If this be the case, it may in some degree account for some of the 

 dark varieties which predominate to such a degree over the light 

 ones, both in a state of nature and in confinement. In many cases I 

 find that some particular variety was bred from the only larva 

 collected. Mr. Porritt has a very dark Quercus which was bred by a 

 non-entomological relation of his, and might have been neglected and 

 obliged to eat withered food ; it also remained in pupa two years 

 before emerging. I have only seen another specimen of this variety, 

 which is in the British Museum. 



There can be very little doubt that many varieties, or local races, 

 are produced by natural selection, and the best instance I know of is 

 Gnophos obsciirata. This insect has the habit of settling on the 

 ground like Belgiaria, and those individuals which difter most from 

 the colour of the ground become the easiest prey to the birds ; hence 

 on the black peat we find a very dark insect, while on the chalk thev 



