1890] THE YOUNG NATURALIST. 



93- 



ON THE PROBABLE ORIGIN OF D. GALII, 



By W. H. TUGWELL, F.E.S. 



In this journal for May, 1889, Vol. X., p. 113-5, I opened up this 

 subject, and gave my reasons for believing that in all probability the 

 D. galii captured in this County were imigrants. A very important 

 factor in this discussion is, that all captured imagines of D. galii that 

 preceed what we call galii years, are invariably considerably larger, 

 than any that are bred from larvae found feeding in England. Greater 

 in expanse of wing, heavier in body, and generally heavier and more 

 robust looking. This holds good not only on the last occasion, 1888, 

 but on the great galii years of 1869 and 1870 also. In expanse of wing, 

 the captured imagines are fully § of an inch more on the average than 

 bred specimens, and I challenge anyone to show an English bred and fed 

 galii expanding full 3^ inches in the male, or 3! inches in the female. 

 Captured imagines give these sizes regularly. Can Mr. Briggs explain 

 this? It is not a question of being fed in confinement, and fed at large, 

 for large numbers of larvae have been found quite full fed, and pupae 

 also have been obtained repeatedly, but they never produced insects 

 of the size of their parents. To my mind the reason is abundantly 

 clear. Our want of sunny skies, and our cold wet autumn weather, 

 prevents a healthy and full development of this species. This has 

 been my principal argument all though, and it has convinced me that 

 our captured imagines are all or nearly all immigrants. Hundreds of 

 pupae must have been left in our various sandhills in 1888, but how 

 many moths were seen in 1889? How many larvae were found in the 

 autumn? Echo answers, how many? 



Is Mr. Briggs really serious when he says in the April number, 

 that I have executed a " Volte face" or is it a joke for the first of April. 

 I have clearly proved that his list dates when imagines were captured, 

 are of no value in this argument. He cites Mr. J. A. Cooper's capture 

 of larvae in Suffolk as telling against my theory, but I doubt he hardly 

 grasps my theory. I make no exception in asserting that the parents 

 of all our 1888 larvae were immigrants, whether found at Wallasey, 

 Suffolk, Kent, or elsewhere. Further, I do not believe that any Eng- 

 lish fed galii ever produces another progeny here. Can Mr. . Briggs 

 produce any evidence to the contrary ? It should not be difficult to do 

 so if such evidence exists, and I am quite open to conviction. But were 

 Mr. Cooper's larvae any earlier than those on the Deal sandhills ? I 



