Chap. VIII. SEXUAL SELECTION. 311 



numerous. Several entomologists concur in this view. Mr. Double- 

 day, however, and some others, take an oj3posite view, and are con- 

 vinced that they have^ reared from the egg and caterpillar states a 

 larger proportion of males than of females. 



Besides the more active habits of the males, their earlier emerg- 

 ence from the cocoon, and their frequenting in some cases more 

 open stations, other causes may be assigned for an apparent or real 

 difference in the proportional numbers of the sexes of Lepidop- 

 tera, when captured in the imago state, and when reared from the 

 egg or caterpillar state. It is believed by many breeders in Italy, 

 as 1 hear from Professor Canestrini, 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 

 surrounded by caterpillars would probably devour the largest ; and 

 Professor Canestrini informs me that in Italy some breeders believe, 

 though on insufficient evidence, that in the first brood of the 

 Ailanthus silk-moth, the wasps destroy a larger number of the 

 female than of the male caterpillars. Dr. Wallace further remarks 

 that female caterpillars, from being larger than the males, require 

 more time for their development and consume more food and mois- 

 ture ; and thus they would be exposed during a longer time to 

 danger from ichneumons, birds, &c, 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 the 

 numbers at maturity, when the sexes are ready to propagate their 

 kind. 



The manner in which the males of certain moths congregate in 

 extraordinary numbers round a single female, apparently 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 fwenty males may often be 

 seen congregated round a female Elacliista rufocinerea. Jt is well 

 known that if a virgin Lasiocainpa quercus or iiaturnia carpini 

 be exposed in a cage, vast numbers of males collect round her, 

 and if confined in a room will even come down the chimney to her. 



