CH. II.] METAMORPHOSES OF INSECTS. 45 



metropolis every third or fourth year. The fine 

 white bordered butterfly (Vanessa antiopa) is another 

 instance of this irregularity. Mr. Haworth remarks 

 upon this insect, " There is something very extra- 

 ordinary in the periodical but irregular appearance 

 of these species — Edusa and Cardui. They are 

 plentiful all over the kingdom in some years, after 

 which Antiopa will not be seen by any one for eight 

 or ten or more years, and then appear again as 

 plentiful as before. To suppose they come from 

 the Continent is an idle conjecture, because the 

 English specimens are easily distinguished from all 

 others by the superior whiteness of their borders. 

 Perhaps their eggs in this climate, like the seeds of 

 some vegetables, may occasionally lie dormant for 

 several seasons, and not hatch until some extra- 

 ordinary coincidences awake them into active life." 

 And Mr. Stephens observes respecting the same 

 butterfly, " Till about the middle of the last century 

 few specimens had been observed ; but about sixty 

 years since it appeared in such prodigious numbers 

 throughout the kingdom that the entomologists of 

 that day gave it the appellation of the Grand Sur- 

 prise." It also occurred again in plenty in 1789 and 

 1803, since which time it has been seldom met with. 

 The same author elsewhere observes, " The cause 

 of this interesting phenomenon appears inexplica- 

 ble : its solution has baffled the inquiries of ento- 

 mologists, and several speculative opinions have 

 been advanced thereon. By some persons, their 

 sudden increase has been attributed to the previous 

 failures of their enemies, the ichneumons and the 

 soft-billed birds ; by others, to an increased temper- 

 ature ; others again suppose that their eggs lie dor- 

 mant until called into life and vigour by some ex- 

 traordinary latent coincidences. But all these opin- 

 ions are mere conjecture, and they do not suffi- 

 ciently clear up the difficulty, which is rendered 

 more obscure from the fact that several of the in- 



