258 A BOOK OF INSECTS 



allies), have no scent- scales, while these are often markedly- 

 developed in grey nocturnal Lepidoptera. Both attrac- 

 tions may, however, be combined in butterflies, just as 

 in flowers." 



It is a significant fact that the males of certain moths 

 whose females are greatly simplified — their eyes, among 

 other parts, having undergone retrogressive changes — are 

 usually dingy and unattractive. In these cases bright 

 colours would obviously be superfluous, as success in 

 courtship must depend chiefly upon the suitor's speed and 

 keenness of scent. Indeed, the conditions of courtship 

 vary greatly, even among closely related species. Thus, 

 in Britain we have five kinds of swift moths {Hepialus). 

 In three instances the males court the females in the 

 usual way, searching for them among the grass and herb- 

 age where they lie hidden. But the males of the gold 

 swift (H. hectus) and the ghost swift (H. humuli) are both 

 provided with dense tufts of scent hairs on the tibial 

 joints of the hind-legs, and these tufts emit a strong per- 

 fume, compared to pine-apple, which proves an irresistible 

 attraction to the females. They give chase to the males, 

 and literally buffet them into matrimony. Moreover, 

 among some butterflies the common rule of courtship is 

 reversed, the females being far more ardent than the 

 males. This is the case with our three common white 

 butterflies. In such instances — i.e. when the female is 

 either known or suspected to play the chief role in court- 

 ship, her colours are generally more attractive than those 

 of her mate ; and we may conclude that her superior 

 charms are due to the aesthetic preferences of the male. 

 On all counts, therefore, it seems probable that beautiful 

 colours constitute a definite part of the insects' courtship 

 equipment. Nevertheless, a line must be drawn between 

 colours of this kind and those which are merely crude and 



