322 (Uecembui 



disturbed by the plough, that we can now expect to meet with great 

 flights o£ ants. The plough is a ruthless enemy of ants in utterly 

 destroying their nests in arable districts, although a few nests can 

 generally be found about sloping terraces in settled districts where the 

 plough cannot reach ; they are invariably smaller, and the number of 

 individuals in each are much fewer, compared to such existing in un- 

 disturbed parts of the country. The habits of the moving columns of 

 ants observed by Mr. H. W. Bates in the forests of the Amazon 

 valley have been charmingly described by this author, but no on* 

 who has not observed a large flight of T. nitidum could imagine tli( 

 vast numbers which comprise it. They invariably migrate in calm. 

 sultry weather, as it would otherwise be quite impossible for thi^ 

 minute and delicate species to do so during the slightest motion of tlu' 

 air. The last great flight I observed moved very slowly in its course, 

 while their " hum " or motions were only slightly audible ; as we were 

 travelling alongside a wire fence at the time we met the flight, wc 

 halted, and observed that great numbers rested on the posts and wire, 

 and after apparently resting their wings for a few seconds, again rose 

 and joined the swarm, their minute hyaline wings, while resting, 

 reflected beautifully in the sunshine. 



Of late years, the causes of the great abundance of certain species 

 of insects in some seasons have been investigated by several eminent 

 entomologists, but the question is yet far from being settled ; if we 

 consider the delicate structure of the three species, whose appearance 

 in great numbers in the past season I have mentioned, we may safely 

 conclude that the natural conditions requisite for their development 

 were exceptionally favourable during all stages of their existence. 

 The long continuance of calm weather throughout the season would 

 enable them to assemble into large flights, and also explain the appear- 

 ance of numerous other species, which have been exceedingly common 

 during the season. We have now been favoured with two seasons 

 comparatively free from wet or strong weather, both of which are very 

 destructive to insects ; unquestionably, the appearance of certain 

 species in phenomenal numbers in some seasons has an impor- 

 tant bearing on the power and operations of the law of natural 

 selection among insects, but at present 1 leave the main features of 

 the case, and with the aid of further observations, which I hope to 

 gather during the coming season, shall endeavour to more clearly 

 elucidate this important and inviting subject. 



East Belt, Asliburton, N.Z. : 



Septemher d(h, 1890. 



