XXVIII. 



PERIODICITY IN THE APPEARANCE OF BUTTER- 

 FLIES 



Every year we read in the pages of our ento- 

 mological journals something about the rarity or 

 abundance of this or that insect. Particularly is 

 this the case with those insects which are agricul- 

 tural scourges, since here the observation of their 

 comparative abundance or scarcity is quickened. 

 It is none the less true, however, of other insects, 

 and among them of butterflies. Indeed, there are 

 comparatively few butterflies which appear in sim- 

 ilar numbers every year. There is always more or 

 less fluctuation in this regard, but we notice it 

 only when their excessive abundance, especially 

 with such swarming butterflies as the Monarch 

 (Anosia plexippus) and the Painted Lady (Va- 

 nessa cardui), or their great rarity causes general 

 comment, at least among entomologists. Some- 

 times we can directly tell the cause of a scarcity, 

 rarely that of a superabundance ; for in the for- 



