832 THE DESCENT OF MAN 



for an apparent or real difference in the proportional num- 

 bers of the sexes of Lepidoptera, when captured in the 

 imago state, and when reared from the egg or caterpillar 

 state. I hear from Prof. Canestrini, that it is believed by 

 many breeders in Italy that the female caterpillar of the 

 silk-moth suffers more from the recent disease than the male, 

 and Dr. Staudinger informs me that in rearing Lepidoptera 

 more females die in the cocoon than males. "With many 

 species the female caterpillar is larger than the male, and 

 a collector would naturally choose the finest specimens, 

 and thus unintentionally collect a larger number of females. 

 Three collectors have told me that this was their practice ; 

 but Dr.' "Wallace is sure that most collectors take all the 

 specimens which they can find of the rarer kinds, which 

 alone are worth the trouble of rearing. Birds when sur- 

 rounded by caterpillars would probably devour the largest; 

 and Prof. Canestrini informs me that in Italy some breed- 

 ers believe, though on insufficient evidence, that in the 

 first broods of the Ailanthus silk-moth the wasps destroy 

 a larger number of the female than of the male caterpil- 

 lars. Dr. Wallace further remarks that female caterpillars, 

 from being larger than the males, require more time for 

 their development, and consume more food and moisture; 

 and thus they would be exposed during a longer time to 

 danger from ichneumons, birds, etc. , and in times of scarcity 

 would perish in greater numbers. Hence it appears quite 

 possible that, in a state of nature, fewer female Lepidoptera 

 may reach maturity than males; and for our special object 

 we are concerned with their relative numbers at maturity, 

 when the sexes are ready to propagate their kind. 



The manner in which the males of certain moths congre- 

 gate in extraordinary numbers round a single female ap- 

 parently indicates a great excess of males, though this fact 

 may perhaps be accounted for by the earlier emergence of 

 the males from their cocoons. Mr. Stainton informs me 

 that from twelve to twenty males may often be seen con- 

 gregated round a female ElacMsta rufocinerea. .It is well 



