OCCASIONAL ABUNDANCE OF LKPIDOPTERA. 61 



the development of Lepidoptera in abundance, while others tend 

 in an opposite direction. But this would apply, and as Mr. 

 Smith tells us in this case did apply, to the great majority of 

 species ; whereas the particular point that I sought to follow up 

 was the cause of the unusual abundance of one or two particular 

 species in seasons when the great majority of species were scarce. 

 Whether cases of sporadic abundance, such as I have 

 indicated, occur in New Zealand, I am not fully aware, but I 

 gather from the writings of Messrs. W. W. Smith and G. V. 

 Hudson that they are not altogether unknown ; and I think we 

 should not too hastily assume that migration can have no 

 bearing upon them, or even upon the abundance or otherwise of 

 Lepidoptera generally. Mr. Smith tells us that, " The main 

 facts adduced to account for the occasional abundance of certain 

 species in the British Islands will not fully apply to the same 

 phenomena in New Zealand," because, as he explains, " the 

 British Islands and New Zealand are both insular areas ; but 

 while the former is separated only by a few miles from the 

 European Continent, the latter is situated at least one thousand 

 miles from the Continent of Australia." And further, that " the 

 migration theory, as explained by Mr. G. V. Hudson (Entom. 

 xxiii. 133), can have no bearing on the question in New Zealand." 

 I cannot admit that this greater distance would form an insur- 

 mountable obstacle to immigration ; if it were so, it seems highly 

 improbable that that essentially New World species, Anosia 

 jjlexippus, would have reached Great Britain (Proc. South Lond. 

 Entom. Soc, 1886, pp. 17, 42, 60) ; and, except for this greater 

 sea-space, the relative position of the British Islands and New 

 Zealand to their respective continental bases are singularly 

 alike. As the former occupies the position of the western 

 boundary of the Asio-European region, so the latter forms the 

 eastern extremity of the Indo-Australian : the lepidopterous 

 fauna of the British Islands is essentially that of its continental 

 base, and that of New Zealand, so far as it has been investigated, 

 appears to belong to the Indo-Australian region. That migra- 

 tions of Lepidoptera from the continental portion of the Euro- 

 pean area to the British Islands do occur has already been 

 shown, and is it not reasonable to suppose that a similar condi- 

 tion of things exists in regard to New Zealand ? 



It is not many years since the annual migration of birds to 

 and from the British Islands was regarded by many as nothing 

 more than a wild theory, but thanks to careful and persistent 

 observation we now know it to be an established fact ; in 

 the course of these observations material has been gathered 

 which points to the conclusion that the occasional migrations of 

 Lepidoptera follow the routes taken by the birds in their annual 

 movements. Should this ultimately prove to be so, a case of 

 bird migration recently reported from Tasmania should be of 



