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AFRICAN MIMETIC BUTTERFLIES 



Pieris, Euterpe, Leptalis, Protogonius, Ithomeis, Castnia, Dioptis, Pericopis, Hyelosia, and 

 others ; some of the latter genera belong to the Heterocera. Bates disposes of the possible 

 question as to why these insects (Heliconinae) should be regarded as the imitators and not 

 the imitated, by pointing out that whilst there is a general resemblance of type between 

 the species of the genus Heliconius, the imitating insects depart more or less widely from 

 their own family types, as though they had been perverted from their normal colour and 

 markings in order to produce the resemblances noted. So accurate was the likeness between 

 many of these forms that Bates remarks that in spite of his long experience he was never 

 able to distinguish the Leptalides from the Heliconinae until after they were captured. The 

 Heliconinae are exceedingly subject to local variation and modification, and it is important 

 to notice that these local forms are accompanied by corresponding species or varieties 

 whose markings continue to follow the design of the models. Apart from the fact already 

 mentioned of the mimicking species being of a type unusual to their genera, Mr. Bates 

 points out that in most cases the models are excessively abundant, whilst the mimics are very 

 rare. Thus the Leptalides were to the Ithomiae which they imitated, in the ratio of about 

 I to 1,000. The Heliconinae are also imitated by several species of moths. Bates, after 

 carefully studying the subject, found that ' those features of the portrait are most attended 

 to by nature which produce the most effective deception when the insects are seen in nature '. 

 The resemblance is not always very striking when the insects are seen in the cabinet, but 

 the author acknowledges that he was constantly deceived when capturing these insects in the 

 woods. Having noted some of the well-known instances of insects resembling in form and 

 colour inanimate objects which are of no interest to their pursuers, the author puts forward 

 the suggestion that the Heliconinae which are the objects of so much imitation by other 

 butterflies are in some way naturally protected from their vertebrate enemies, and that there- 

 fore the mimicking species escape, owing to their superficial resemblance to such protected 

 forms, and he suggested that their protection lies in the fact of their unpalatability. He re- 

 marks that in the whole course of his experience he never saw the Heliconinae attacked by birds, 

 lizards, or other predaceous creatures, such as the Asilidae,'^wh.\[s,i butterflies of other families 

 were frequently pounced upon by such enemies. He also noticed that they all had a peculiar 

 smell, and that the captured specimens were always less subject to the attacks of vermin. 



As previously stated, his explanation of the origin of these mimetic analogies is based 

 on the theory of natural selection. The suggestion that the Heliconinae were in some way 

 protected did not explain the observed fact that some members of the same group are them- 

 selves the imitators; in other words, they ' counterfeit each other '. This phenomenon is 

 one of which at that time no explanation was forthcoming, but the subject was dealt with 

 in a paper by Dr. Fritz Miiller in May, 1879, a translation by Professor Meldola being pub- 

 lished in the Proceedings of the Entomological Society of the same year. This paper deals 

 with a specific case of mimicry between Ituna ilione and Thyridia megisto. The two genera 

 are considered to belong to the Danainae, and both possess distasteful qualities. Miiller 

 points out that although the two genera are closely related, the resemblance is not due 

 to consanguinity, but has been acquired by imitation, in support of which conclusion he 

 refers to the fact that their progenitors, judging from the large number of existing species, 

 presumably had the wings covered with scales, and not transparent as in these two cases. 

 It may be noted here in parenthesis, that the resemblance, mainly caused by the transparent 



^ In view of more recent research, it seems probable that the Heliconinae are in fact preyed upon by the 

 Asilidae. See Poulton, Trans. Ent. Soc, 1902, p. 336. 



