24 



definite records of its occurrence in greater or less abundance in 

 1797. 1804, 1808, 1811, 1818, 1822, 1826, 1831, 1835, 1836, 1839, 

 1843, 1844, 1855, 1856, 1857, 1859, 1864, 1865, 1867, 1868, 1869, 

 1875, 1876, and then came the memorable year 1877. The species 

 had been locally common in the two preceding years, and then in 

 1877 it spread over the whole country in the greatest profusion, 

 extending even as far north as Orl<ney.^^ Another year of great 

 abundance was 1892, but unlike 1877 the advent was particularly 

 sudden, there being no records, so far as I have been able to ascer- 

 tain, either for 1890 or 1891. Since that time we have had many 

 years of bounty and of scarceness, but none so remarkable as those 

 of 1877 and 1892. 



The authors who followed Donovan during the first half of the 

 nineteenth century appear to have had no very strong views on the 

 reasons for the insect's erratic appearances. Curtis (1832) simply 

 writes, " it is said that C. ediisa visits us every three or five years ; 

 however this may be, it is certain that it is occasionally abundant 

 in various parts of the kingdom, although for several years succes- 

 sively not a specimen will be seen."" Westwood (1841) says, " This 

 is one of those species of butterflies whose periodical appearance 

 (every three or four years, as stated by some writers) has so much 

 perplexed Entomologists. Various opinions have indeed been sug- 

 gested by authors, in order to account for this singular circumstance 

 — such as the failure of their natural enemies, the Ichneumonidae, 

 or insectivorous birds — an increased temperature, or the dormant 

 state of the eggs until called forth by some latent coincidences. All 

 these opinions are, however, but merely conjectural; nor can the 

 matter be cleared up until a more minute enquiry into the habits of 

 the species has been made."^'^ While Humphreys (1859) remarks, 

 "Its abundance once in three or four years has not been satis- 

 factorily explained."^'' It would therefore seem that the train of 

 thought at this period was that the species by some mysterious 

 agency was of common occurrence at stated periods, some seeking 

 to show that it was at intervals of three, four or five years, accord- 

 ing to their fancy, but no one apparently taking any great amount 

 of trouble to solve the mystery. 



In 1867 Buckler obtained ova from June parents, and had no 

 difficulty in leariqg a full autumn brood from them ; and ten years 

 later he repeated the experiment with ova from August females, but 

 from his notes the result is not very clear ; some few reached the 

 pupa stage by the end of October, but what subsequently happened 

 to them is not stated." Although this did not give any great 



13 Dale. " The History of our British Butterflies," pp. 30-31. 

 " Curtis. "Brit. Entomology," vol. v.. p. 242. 



15 Humphreys and Westwood. "British Butterflies and their Trans- 

 formations," p. 15. 



"' Humphreys. " Genera and Species of Brit. Butterflies," p. 3. ' 



17 Buckler. " The Larvse of the Brit. Butterflies," vol. i., p. 9. 



