412 THE DESCENT OF MAir 



Bome of these species have the habit of "holding their 

 wings quite erect over their backs, retaining them in this 

 position for a considerable time," and thus exposing the 

 under surface to view. Other species, when settled on 

 the ground or herbage, now and then suddenly and slightly 

 lift up their wings. Hence the lower surface of the wings 

 being brighter than the upper surface in certain moths is 

 not so anomalous as it at first appears. The Saturniidse 

 include some of the most beautiful of all moths, their wings 

 being decorated, as in our British Emperor moth, with fine 

 ocelli; and Mr. T. W. Wood" observes that they resemble 

 butterflies in some of their movements-; "for instance, in the 

 gentle waving up and down of the wings as if for display, 

 which is more characteristic of diurnal than of nocturnal 

 Lepidoptera." 



It is a singular fact that no British moths which are 

 brilliantly colored, and, as far as I can discover, hardly 

 any foreign species, difEer much in color according to sex; 

 though this is the case with many brilliant butterflies. 

 The male, however, of one American moth, the Saturnia 

 lo, is described as having its fore-wings deep yellow, curi- 

 ously marked with purplish red spots; while the wings of 

 the female are purple-brown, marked with gray lines." 

 The British moths which differ sexually in color are all 

 brown, or of various dull yellow tints, or nearly white. 

 In several species the males are much darker than the 

 females,"" and these belong to groups which generally fly 



■8 "Proc. Eut. Soe. of London," July 6, 1868, p. xxvii. 



" Harris, "Treatise," etc., edited by Flint, 1862, p. 395. 



*" For instance, I observe in my son's cabinet that the males are darker 

 than the females in the Lasiocampa quercus, Odonestis potatoria, Hypogymna 

 dispar, Dasychira pndibunda, and Cycnia mendica. In this latter species the 

 difEerence in color between the two sexes is strongly marked ; and Mr. Wallace 

 informs me that we here have, as he believes, an instance of protective mimicry 

 confined to one sex, as will hereafter be more fully explained. The white female 

 of the Cycnia resembles the very common Spilosoma menthrasti, both sexes of 

 which are white; and Mr. Stainton observed that this latter moth was rejected 

 with utter disgust by a whole brood of young turkeys, which were fond of eat- 

 ing other molhs; so that if the Cycnia was commonly mistaken by British birds 

 for the Spilosoma, it would escape being devoured, and its white deceptive color 

 would thus be highly beneficial. 



