THE YOUNG NATUBALIST. 



129 



the attempts that have been made to explain them away, have in most cases 

 met with no small amount of success. 



The statement in the first premise that " several species are only keeping 

 on our lists by immigration," is surely irrelevant to Mr. Robson's inquiry. 

 To make it relevant it would be necessary to show that at some time or other 

 these species were true natives of the British Isles, and I cannot find that 

 Mr. Eobson adduces a shadow of proof that any of them ever were so. 

 The remainder of the premise is, of course most material, though I cannot 

 help thinking it somewhat over strongly stated. 



The modifications which I have considered it necessary it to make in Mr. 

 Robson's premises, force me to come to a conclusion somewhat different from 

 his. In my opinion though there is certainly a process of extinction of our 

 our butterflies going on, owing to causes which I shall presently attempt to 

 explain. Yet this process is one of such a very gradual nature, that the time 

 is still exceedingly " far distant when a large proportion of our butterflies 

 will have ceased to exist as natives." There is at the present time an indica- 

 tion among entomologists to exaggerate the number of " disappearances " of 

 butterflies, owing to the fact that the wet years we have had lately have tempor- 

 arily greatly reduced the number of specimens of almost all the species of our 

 British butterflies. But these wet years can be no new experience to them. 

 They must have weathered a succession of bad years before, and I confidently 

 expect to see them reappear after a few fine summers, in numbers but slightly 

 diminished. Only before the growth of our towns, and the all-destroying 

 smoke of our factories, will the greater number of our species absolutely die 

 out. 



The second of the two main conclusions to which I referred, is that the 

 causes of the diminution of the numbers of our butterflies, are " our mild open 

 winters, cold ungenial springs, rainy and sunless summers." I do not know 

 whether the mild open winters, and so on, are intended to typify the climate of 

 England under ordinary circumstances, or the peculiarly unfavourable weather 

 which we have been experiencing of late years. If the former, I do not 

 think that had more than a very slight influence upon the decrease of the 

 numbers of our butterflies ; if the latter, I would remark that a species whose 

 disappearance only dates from '77 or '78 has not been gone long enough to 

 make it at all improbable that with fine weather it will reappear. The 

 main cause of all permanent disappearances of our butterflies is not the 

 climate but man, and that I shall presently endeavour to show. There is 

 another matter which, in the opinion of at least one of our leading lepidop- 

 terists, is likely to exercise, if it is not already exercising, an unfavourable 

 influence upon the numbers of our British butterflies, and that is the large 



