69 



we have noted. But there are other species that it will be 

 necessary to refer to before we attempt to draw conclusions. 



Pieris brassiccB, L., as we all know, is one of the most 

 generally distributed of the British butterflies ; it occurs 

 more or less plentifully in all parts of the United Kingdom, 

 and its range extends throughout the Continental area, ex- 

 cepting only the polar regions ; indeed, we are so accustomed 

 to regard it as a common insect, that we are apt to attach 

 but little importance to its appearance in increased or 

 diminished numbers ; but its abundance has on rare occasions 

 been so great as to actually thrust itself upon our attention. 



This was the case in 1887, and as a consequence we find 

 some few records regarding the species ; from these it would 

 appear that in the autumn of the previous year the larvae had 

 been somewhat abundant in some parts of Sussex, but we 

 fail to hear that the imago was so in the spring of 1887 as we 

 might have expected it to be. As the year progressed we 

 again had reports of the local abundance of the larva, now 

 from the east of London and the north-east of Ireland, as 

 well as the Sussex localities ; and with the approach of 

 August the imago was suddenly swarming throughout the 

 south and midlands, and in many parts of the north, but by 

 the following spring (1889) the wave of abundance had passed 

 and we found that the species was not then unusually 

 common. This is no doubt but an example of what is 

 frequently taking place ; and looking at it as it stands, and 

 taking into account the particularly warm dry summer of the 

 year, we appear to have sufficient reasons for attributing the 

 abundance to local reasons ; but we must not shut our eyes 

 to other possible agencies.^ 



Mr. C. G. Barrett tells of a perfect swarm of this species 

 that he fell in with on the very coast at Hunstanton, although 

 he had seen but a casual specimen or two on his way thither 

 from Lynn, nor did he find them in any such numbers further 

 inland, and he concluded that he had come upon a troop of 

 immigrants before they had had time to disperse ; this was 

 at the end of May, 1887 {E.M.M. xxiv. 85). In previous 

 years we also find some few notes of the movement of 

 large numbers of this species ; for instance, they have been 

 observed coming into the North Lincolnshire marshes across 

 the Humber from the Yorkshire coast, some four and a half 

 miles distant ; the flight is said to have resembled snovv- 



^ It is worthy of note that although Pieris brassiccz and P. rupee were so 

 abundant, P. napi was less common than usual, and appeared to be almost absent 

 from many districts where it usually occurs in some numbers. 



