THE ENTOMOLOGIST. 



Vol. XI.] 



MARCH, 1878. 



[No. 178. 



C L I A S E D U S A, 

 By Edwauij A. Fiich. 



Egg of C. Edusa magnified ; eggs (slightly maguified) on clover leaf; portion 

 of egg, showing the converging longitudinal ribs. Pupfe of C. Edusa: 

 dorsal and lateral view. 



The unusual abundance, or abnorraal occurrence, of certain 

 insects in certain years, has long been a subject for varied 

 hypotheses and speculations. Some have been disproved, 

 others to a certain extent explained by a better acquaintance 

 witli the economy of the noted species; e.r/., the swarms of 

 Aphides being followed by the swarms of Cocc/Hetlidce, 

 Syrphidce and Hemerobidce, is a familiar instance of the 

 inspired afdiorism that — " Wheresoever the carcase is, there 

 will the eagles be gathered together." The occasional swarms 

 of certain Diptera are also explicable by reference to their 

 economy. Amongst Lepidoptera our two species of Colias 

 have been noted par excellence lor their periodic appearance. 

 The older observers, believing in a hard-and-fast line, sum- 

 marised that period as triennial, quadrennial, quinquennial, 

 or septennial, each period being defended according to the 

 immediate, though limited, exj^erience of the individual. 

 Mr. Desvignes' septennial theory still lingers, probably owing 



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