COLIAS HYALE. 65 



even over the Border. Then may follow several years 

 during which very few will be seen, till a fear almost 

 arises that the species may be dying out a fear to be 

 set at rest by another season of surpassing plenty. Edusa, 

 however, seems to have established itself more firmly of 

 late as a British butterfly. Entomologists have found 

 these capricious appearances a very difficult problem to 

 solve ; in fact, no satisfactory solution seems to have 

 been found. Some have suggested that individuals 

 have been blown, or of their own free will have flown, 

 across the sea from the Continent, and these, breeding 

 here, have produced the plentiful autumn flight of butter- 

 flies. It has also been suggested that some seasons the 

 eggs or pupoe may lie dormant, and so the butterflies of 

 several seasons may all appear in one. But the plants 

 on which the eggs are laid are scarcely "of a nature to 

 preserve them for any length of time. It may be that 

 some years few survive the winter, and leave their 

 hibernacula in the spring, while more do so in 

 others. It was at one time thought that a plentiful 

 season occurred once in seven years ; but there have 

 been too many exceptions to allow much faith being put 

 in the supposition, which, however, was not altogether 

 unwarranted. 



C. hyale, Linn. (Pale Clouded Yellow or Clouded 

 Sulphur) (Figs. 52 and 53), is, like its congener, very 

 swift on the wing, and haunts similar localities, but is 

 by no means so common. Indeed, it must be looked 

 upon generally as a scarce butterfly, though in the south- 

 east of England it occasionally appears in profusion, and 

 singularly enough during the earlier part of the present 

 century these seasons of profusion occurred once every 

 seven years for several times in succession. This came to 

 be looked upon as a law till 1849, since which it has failed. 



