Ill 



ON THE EVIDENCE THAT SOME BUTTERFLIES 

 ARE MORE PALATABLE THAN OTHERS 



It has been seen that one of the objections which has been raised against mimetic 

 theories is that there is insufficient evidence that the so-called protected species are in fact 

 unpalatable. It was on the assumption of the unpalatability of certain forms that Bates 

 founded his theory of the mimetic resemblances to which he called attention in his original 

 memoir already described in our introductory chapters. In inquiring what advantages the 

 Heliconidae possess to make them 'so flourishing a group, and consequently the objects 

 of so much mimetic resemblance he remarks that they are probably unpalatable to their 

 enemies. He observes that ' recently killed specimens of the Danaoid Heliconidae, when set 

 out to dry, were always less subject than other insects to being devoured by vermin. They 

 all have a peculiar smell. I never saw the flocks of slow-flying Heliconidae in the woods 

 persecuted by birds or dragonflies, to which they would have been an easy prey, nor when 

 at rest on leaves did they appear to be molested by lizards or the predaceous flies of the 

 family Asilidae, which were very often seen pouncing on butterflies of other families '. 



Trimen's paper on * Mimetic Analogies among African Butterflies ' ^ was published in 

 1869, and gave strong confirmation of Bates's view that some insects are distasteful. On 

 this subject he writes as follows : ' The peculiar smell noticed by Mr. Bates in the Heliconide 

 Danaidae is also possessed by the Euploeae of the Eastern Archipelago, as Mr. Wallace has 

 recorded ; and I am enabled to add similar evidence as regards the African species of Danais 

 and Acraea. (The Mauritian Euploea euphone also gives out a strong odour when handled.) 

 Judging from the case of Acraea horta, a widely distributed African species, which I have 

 reared in considerable numbers from the young larvae, this disagreeable smell is not peculiar 

 to the imago condition, but attends the insect throughout its life, even the pupae emitting it. 

 On pressing the thorax of a Danais, a Euploea, or an Acraea, however slightly, a clear yellow 

 liquid similar to that secreted by the Ladybird beetles, almost always exudes from that 

 part of the body : and in some species of the two former genera a pair of bright yellow fascicled 

 appendages are protruded from the extremity of the abdomen. The peculiar scent appears 

 chiefly to reside in this liquid, being remarkedly stronger with each effusion. Most of the 

 species of Danais and Acraea feign death very readily ; and they possess another means of 

 defence which, as far as I am aware, has not hitherto been recorded, viz. the remarkable 

 elasticity of their entire structure. No pressure of the thorax, short of absolute crushing of 

 the tissues, suffices to kill or even paralyse these butterflies ; and the collector who treats 

 them as he would species of other families, soon finds his collecting-box alive with struggling 

 occupants. ... It is not difficult to perceive how important, as a reserve means of defence, 

 this unusual elasticity of structure may prove. That birds and other eaters of insects 

 may occasionally capture a butterfly of these malodorous tribes before discovering its 

 distasteful character is not an unreasonable supposition, especially in seasons when an 

 exceptional scarcity of food may prevail. In such a case it may be safely stated that the 

 chances are very greatly in favour of a Danais or an Acraea escaping, if not wholly unhurt, 



^ Trans. Linn. Soc, voL 26, pt. iii, i86g. 



