1911] on the Scents of Butterflies. 83 



ribs apparent in the "battledore" are in all probability lioniologous 

 with the longitudinal channels seen in the Pierine plume-scale. These 

 in Jfi/lot/tn's, as we have seen on the screen, take the form of ribs as 

 (Ictinitely marked as those of the Lyca3nids. 



So far, all the scents with which we have been concerned are of a 

 kind that is agreeable to our own senses. But there is another sort 

 of odour which is also commonly present, especially in the butterflies 

 of tropical and subtropical regions, and which, instead of being 

 pleasant to the human sense, is disagreeable or even repulsive. The 

 Acraias, which are mostly reddish or brownish butterflies with small 

 dark spots ; the Euploeas, large butterflies which often show a 

 brilliant purple gloss hke that of our own Purple Emperor ; the 

 Papilios, of which a good example is the black and yellow Swallowtail 

 butterfly of the Cambridgeshire fens, have many of them an odour 

 which may be called disgusting. Musty straw, stable litter, rabbit- 

 hutches, acetylene, bilge-water, these are some of the substances to 

 which the odours of these unsavoury butterflies have been compared. 

 In some cases, as in the instance of the agreeable perfumes, the seat 

 of these evil-smelling odours has l)een found in patches or tufts of 

 specialised scales or hairs : in others the scent appears to be emitted 

 from the general wing-surface. But in no instance, so far as I am 

 aware, has any structure like a plume-scale been found guilty of 

 emitting anything but a pleasing fragrance. A very remarkable 

 difference l)etween the scents pleasant and the scents unpleasant is 

 this : that the former kind usually, though not invariably, is confined 

 to the male sex ; while the latter kind is common to both sexes, 

 being often indeed stronger in the female. 



It has, no doubt, occurred to you to ask : has the presence of these 

 scents any particular significance with regard to the needs of their 

 possessors ; and if so, what ? And why should the agreeable scents 

 be so commonly confined to the one sex, while the repulsive odours 

 are shared by both ? 



The second question helps us to answer the first. With regard to 

 the scents of the disagreeable kind, which are probably often accom- 

 panied by a nauseous flavour, there is good reason to suppose that 

 they are in effect a means of protection from insect-eating enemies. 

 We have much actual evidence bearing upon the point. Evil-smelling 

 butterflies, like the Acraeas or the well-known Limnas chrysippus (a 

 large brown butterfly common throughout many parts of Africa and 

 Asia), are often conspicuous, slow-flying, and given to courting obser- 

 vation rather than to avoiding it. These are all marks of butterflies 

 which are more or less immune from attack by birds ; and it may be 

 added that the frequency with which many of them are copied by 

 other butterflies gives further reason for the conclusion that they 

 enjoy protection in virtue of their distasteful qualities — a protection 

 which other butterflies are enabled to share by resembling them in 

 outward appearance. 



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