Ixxxix 



MIMICEY IN SILK- WORM MOTHS. 



(With Plates I, II and III). 



The phenomenon of Mmiicry, as presented by Lepidoptera, affords a most 

 fascinating study to those who go about the world with their eyes open- 

 even though they may not happen to be students of entomology. For 

 instance, what beginner at collecting has not been struck by the startling 

 resemblance of the female of Hypolimnas onisippus (Linn.), to the com- 

 mon Danais chvysippus (Linn.) ? or by that of the moth Epicopia rolydora 

 (Westw.) to the Papilios of the Philoxeniis group .P— just to mention two very 

 self-evident instances. What is the meaning of it ? and why should D. 

 chrydppm be such an exceedingly common butterfly ? are questions which 

 suggest themselves to us at once. These are phenomena which are 

 presented to us, and it is " up to " us to endeavour to account for them in 

 some reasonable manner, and not to pass the problems by as insoluble. 

 In endeavouring to account for them, however, one fundamental rule must 

 not be lost sight of, which is that the imitator and it's model must be or 

 must recently have been inhabitants of the same locality, otherwise the 

 whole theory of mimicry falls to the ground. As it happens, the solution 

 of the apparent enigma referred to above is a simple one : the sub-family 

 DanaincB to which D. chrysipp)us belongs have, as we all know, acquired the 

 faculty of being distasteful to the many insectivorous birds and reptiles 

 which prey upon, butterflies and moths, and so enjoy immunity from their 

 attacks, and are consequently, numerous in individuals ; and further, some 

 of those forms, which do not possess this faculty, have gradually become 

 developed in imitation of their more fortunate comrades, in accordance 

 with the Darwinian Law of the survival of the fittest. The immunity of 

 these specialized forms has probably been acquired as follows : — the larvse 

 of many of them are known to feed on Aristolochia indica, Gomphocarpus 

 fruticosus and other Asclepiad plants which, when cut, exude a white 

 milky substance which is exceedingly bitter to the taste, and the inference 

 is that this quality is transmitted to the imagines and renders them dis- 

 tasteful. The Philoxenus group of Papilio is also protected by possessing, as 

 imagines, a disgustingly rank odour, somewhat resembling musk, which is 

 so strong and enduring that it remains even after the death of the insect. 



Still the theory of protective imitation is a thorny subject to tackle, and 

 it is with considerable difiidence that I write this paper dealing with 

 another forms of mimicry as exemplified by forms of the family Saturniidoe 

 (or silkworm moths). Any observer who has studied the family must have 

 been struck by the faithful representation of a snake's head, which appears 

 on both sides of the apex of the forewing in the various forms of the genus 

 Attacus and other allied genera of Satumviadcs ; in other words, the apex 

 of the forewing of these forms appears to have been developed in imita- 

 tion of the head of some snake : this phenomenon is apparent at once to 

 anyone who places a piece of paper over a specimen in the cabinet, so as to 

 cover up the whole insect from view except the apical half of the forewing. 



I have figured the apices of the forewing of seven forais of SaturniiadcB 

 in my collection, which exhibit this character with greater or less fidelity, 

 the two most striking representations being undoubtedly Attacus atlas 

 and Attacus edwardsi, the former of which exhibits the snake's head in 

 profile and the latter gives a view of the head from above, showing both 

 eyes : the remaining forms though, perhaps, not so striking, give, never- 

 theless, an accurate delineation of a serpent's head, and point to general 

 tendency towards snake mimicry in this family in forms from the JEthio- 

 pian and Nearctic regions as well as the Oriental. 

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