3 1 6 The Descent of Man. Part ] I. 



It is a singular fact that no British moths which are bril- 

 liantly coloured, and, as far as I can discover, hardly any foreign 

 species, differ much in colour according to sex ; though this is 

 the case with many brilliant butterflies. The male, however, of 

 one American moth, the Saturnia Io, is described as having its 

 fore-wings deep yellow, curiously marked with purplish-red 

 spots ; whilst the wings of the female are purple-brown, marked 

 with grey lines. 19 The British moths which differ sexually in 

 colour are all brown, or of various dull yellow tints, or nearly 

 white. In several species the males are much darker than the 

 females, 20 and these belong to groups which generally fly about 

 during the afternoon. On the other hand, in many genera, as 

 Mr. Stainton informs me, the males have the hind-wings whiter 

 than those of the female — of which fact A grot is exclamationis 

 offers a good instance. In the Ghost Moth (Hepialus liumuli) 

 the difference is more strongly marked ; the males being white, 

 and the females yellow with darker markings. 21 It is probable 

 that in these cases the males are thus rendered more conspicuous, 

 and more easily seen by the females whilst flying about in 

 the dusk. 



From the several foregoing facts it is impossible to admit 

 that the brilliant colours of butterflies, and of some few moths, 

 have commonly been acquired for the sake of protection. We 

 have seen that their colours and elegant patterns are arranged 

 and exhibited as if for display. Hence I am led to believe that 

 the females prefer or are most excited by the more brilliant 



19 Harris, ' Treatise,' &c, edited which were fond of eating other 

 by Flint, 1862, p. 395. moths ; so that if the Cycnia was 



20 For instance, I observe in my commonly mistaken by British birds 

 son's cabinet that the males are for the Spilosoma, it would escape 

 darker than the females in the being devoured, and its white de- 

 Lasiucampa quercus, Odonestis pota- ceptive colour would thus be highly 

 toria, Hypogymni disp:t?', DasycUira beneficial. 



pudibunda, and Cycnia mendica. In 21 It is remarkable, that in the 



this latter species the difference in Shetland Islands the male of this 



colour between the two sexes is moth, instead of differing widely 



strongly marked ; and Mr. Wallace from the female, frequently rc- 



informs me that we here have, as sembles her closely in colour (see 



he believes, an instance of protective Mr. MacLachlan, 'Transact. Ent. 



mimicry confined to one sex, as Soc.' vol. ii. 1866, p. 459). Mr. 



will hereafter be more fully ex- G. Fraser suggests ('Nature,' April 



plained. The white female of the 1871, p. 489) that at the season of 



Cycnia resembles the very common the year when the ghost-moth ap- 



Spilosonia menthrasti, both sexes of pears in these northern islands, the 



which are white ; and Mr. Stainton whiteness of the males would not 



observed that this latter moth was be needed to render them visible tc 



rejected with utter disgust by a the females in the twilight night, 

 whole brood of youDg turkeys, 



