326 Insects and their Surroundings 



male of his charms take place, there can be no doubt 

 that this "sexual selection" has operated. But among 

 insects no such selection on the part of the females has 

 been shown to occur, except perhaps among grass- 

 hoppers and other stridulating insects whose males 

 charm the females by their shrill chirping (192). 



On the other hand the suggestion has been made 

 that the comparatively dull hues of female animals are 

 due to the action of natural selection in preserving, 

 through many generations, the least conspicuous or 

 best protected individuals. It is believed that female 

 insects are in greater danger from enemies than males ; 

 they necessarily take up exposed positions while laying 

 eggs and are, as a rule, less active than the males in 

 escaping from pursuit. Therefore a rigid selection 

 has prevented the adornment of the female to anything 

 like the same degree as her mate (88). 



The facts mentioned above (p. 322), with regard to 

 the Indian butterflies, Hypoli77i?7as bol'ma and H. misippiis, 

 whose females are mimics of danaine species, while the 

 males retain the usual coloration of their genus, give 

 support to this last view. If, as is highly probable, 

 mimicry be a result of natural selection, we see in 

 these insects how that agency has acted on the appear- 

 ance of the females only, for their protection, leaving 

 the males unaffected. But in very many cases of 

 striking sexual difference, it is evidently the male that 

 has become modified while the female retains the 

 primitive colour of her group. The Swift Moths 

 (Hepialidfe) are a family characterised by brown or 

 golden-coloured wings, but in the largest British 

 species — Hepialus hiimiiU — the male has pure white 

 wings. The group of Ermine moths (Spilosoma and 

 allied genera) are characterised by wings of a white 

 or yellow ground colour •, in the female of Diaphora 

 mend'ica they are semi-transparent white, but in the 



