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Show 310 THE PRINCIPLES OF PART II. Walsh, who informed me of this statement, says that with P. turnus this is certainly the case. Jn South Africa, Mr. R. Trimen found the males in excess in 19 species ;58 and in one of these, which swarms in open places, he estimated the number of males as fifty to one female. With another species, in which the males are numerous in certain localities, he collected during seven years only five females. In the island of Bourbon, M. Maillard states that the males of one species of Papilio are twenty times as numerous a~ the females.o9 Mr. Trimen informs me that as far as he has himself seen, or heard from others, it is rare for the females of any butterfly to exceed in number the males; but this is perhaps the case with three South African species. Mr. vVallace 60 states that the females of Ornithoptera crresus, in the Malay archipelago, arc more common and more easily caught than the males ; but this is a rare butterfly. I may here add, that in Hyperythra, a genus of moths, Guenee says, that from four to five females are sent in c::>llections from India for one male. When this subject of the proportional numbers of the sexes of insects was brought before the Entomological Society,61 it was generally admitted that the males of most Lepidoptera, in the adult or imago state, are caught in greater numbers than the females; but this fact was attributed by various observers to the more retiring habits of the females, and to the males emerging earlier from the cocoon. This latter circumstance is well known to occur with most Lepidoptera, as well as with other insects. So that, as M. Personnat remarks, the males of the domesticated Bombyx Yamamai, are lost at the beginning of the season, and the females at the end, from the want of mates.62 I cannot however persuade myself that these causes suffice to explain the great excess of males in the cases, above given, of butterflies which are extremely common in' their native countries. Mr. Stainton, who has paid such close attention during many years to the smaller moths, informs me that when he collected them in the imago state, he thought that the males were ten times as numerous as the females, but that since he has reared them on a large scale from the caterpillar state, he is convinced that the females are the most ~s Four of these cases are given by Mr. Trimen in his 'Rhopalocera Africre Australis.' ~g Quoted by Trimen, 'Transact. Ent. Soc.' vol. v. part iv. 1866, p. 330. 60 ' Transact. Linn. Soc.' vol. xxv. p. 37. 61 'Proc. Entomolog. Soc.' Feb. 17th, 1868. 62 Quoted by Dr. Wallace in 'Proc. Ent. Soc.' 3r<l series, vol. v. 18fi7, p. 481. I( 'HAP. VIII. SEXUAL SELECTION. 311 numerous.- Several entomologists concur in this view. Mr. Double(. lay, however, and some~others, take an opposite view, and are convinced 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 emercrence from the cocoon, and their frequenting in some cases mo~e ·Open stations, other causes may be assigned for an apparent or real ·difference in the pr~portio~al numbers of the sexes of Lepidoptera, when captured m the Imago state, and when reared from the .egg or caterpillar state. It is believed by many breeders in Italy, .as 1 ~ear from Professor Canestrini, that the female caterpillar of .the s1lk-moth suffers more from the recent disease than the male· .and Dr. S~au~inger informs me that in rearing Lepidoptera mor; females d1e 1~ th~ 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 :mrrounded by caterpillars would probably devour the larcrest · and Professor Cancstrini informs me that in Italy some breede;s beiieve .though on insufficient evidence, that in the first brood of th; ~ilanthus silk-moth, the wasps destroy a larger number of the icmale than of the male caterpillars. Dr. \Vallace further remarks .that fe~ale cater~illars, from being larger than the males, require more time for their development and consume more food and moisture; and t~us they would be exposed during a longer time to ·da~ger ~rom IChneumons, birds, &c., and in times of scarcity would pensh m greater numbers. Hence it appears quite possible that, m a state of nature, fewer female Lepidoptera may reach maturity than males; and for our special object we are concerned with the n~mbers at maturity, when the sexes are ready to propagate their lund. The ~anner in which the males of certain moths congregate in -€Xtraordinary 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 twenty males may often b~ ~;een congregated round a female Elachista rufocinerea. It is well known that _if a virgin Lasiocampa quercus or Saturnia carpini be exposed m a cage, vast numbers of males collect round her .and if_confined in a room will even come down the chimney to her: |
