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49 



The caterpillar, which is naked, cylindrical and slightly villose, is deep green with 

 a longitudinal white stripe on each side marked with yellow spots and minute bluish 

 dots ; it feeds upon Cytisus austriacus on the continent, but as that is not a British 

 plant, it probably feeds upon Medicago lupulina or other papilionaceous plants in this 

 country. Boisduval indeed states that its food consists of the Medicago, Trifolium, 

 and other leguminose plants. 



This insect frequents the blossom of lucerne in preference to that of any other 

 plant, at the end of August. It is not rare in the southern part of England, especially 

 preferring the sea coast, as Dover, Brighton, the back of the Isle of Wight, and the 

 Channel islands, although occasionally found plentifully near London. Boisduval 

 gives Europe, Egypt, the coast of Barbary,— Nepaul, Cachemire, Siberia, and North 

 America, as the range of this species. Mr. Kirby has also described it in his Fauna 

 Boreali-Americana, but has pointed out some distinctions between the American and 

 European individuals. 



This is one of those insects whose periodical appearance in certain but indeter- 

 minate years has so much perplexed entomologists. The other species of this genus, 

 as well as Cynthia Cardui and Vanessa Antiopa, are subject to this irregularity, — 

 Colias Electra being supposed to occur every three or five years, whilst V. Antiopa 

 will not be seen for eight, ten or more years, and then appear as plentiful as before. 

 Mr. Haworth conjectured this might be owing to the eggs having, like the seeds of 

 plants, lain dormant, not hatching until some extraordinary but undiscovered coinci- 

 dences awaken them into active life ; others attribute it to the failure of their natural 

 enemies, as the Ichneumons and soft billed birds ; and others to an increased tempe- 

 rature. But these are mere conjectures, and seem to want confirmation, from the 

 circumstance noticed by Stephens that Cynthia Cardui, although periodical in some 

 places (occurring every third or fourth year) most copiously, and breeding even in 

 the metropolis itself, appears constantly in others. Mr. Bree observes that expe- 

 rience shows that this periodical appearance does not depend on the warmth and 

 fineness of the summer, nor on the mildness of the preceding winter, nor can it be 

 satisfactorily attributed to any known cause ; neither do the peculiar circumstances 

 which conduce to the appearance of C. Electra, have the same effect upon the other 

 species, C. Hyale ; — Mr. Bree stating that whilst, in 1831, C. Electra was abundant 

 near Dover, only one of C. Hyale was taken ; and that in 1832 and 1833, in which 

 so many specimens of C. Hyale were met with, the other was scarcely seen at all. 

 {Mag. Nat. Hist. May, 1836, p. 262.) 



The varieties of this insect have been regarded as distinct species by some 

 writers; Mr. Bree, however, whose practical acquaintance with the species of butter- 

 flies cannot be doubted, as well as Mr. Curtis and others, regard them as belonging 

 to but one species. The variety named Helice by Mr. Haworth, is figured by 

 Stephens, Illustrations, pi. 11.* fig. 3. 9 and by Mr. Bree, Mag. Nat. Hist. No. 26. 

 Mr. Blyth has also made some observations on this species and its varieties, in the 

 41st No. of the same work. The latter gentleman has given, in the same work, a 

 curious instance of the attachment of a number of specimens of this insect to a par- 

 ticular spot, even when driven from it, although he considers it ordinarily to be one 

 of the most rambling and restless of our British butterflies. 



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