3o6 



NATURE 



[January 27, 1898 



are equally mimetic.^ The singular contrast between the 

 numerous modifications of the female of the Bolina type, and 

 the absolutely constant imitation of Danais chrysippus alone by 

 the ? H. misippus is well brought out, and the different courses 

 thus pursued by the respective females are shown to depend on 

 the range, variation, and abundance of the model that is 

 mimicked. Colonel Swinhoe had previously (1887) published a 

 good account of mimicry in Indian butterflies, and in it made 

 special reference to the remarkable series of close likenesses 

 between species belonging to different subgenera of the great 

 protected genus Euplcca. 



Mimicry in Various Orders of Insects, 



So much prominence has naturally been given to the very 

 conspicuous development of mimicry among the Lepidoptera, 

 that it is not uncommon to hear the matter spoken of as if 

 limited to butterfles and moths, and even entomologists need 

 to be reminded of the prevalence of the phenomenon among 

 other orders of insects. The stinging Hymenoptera furnish the 

 most numerous models to members of other orders, being closely 

 mimicked by numerous Diptera, by many heterocerous Lepi- 

 doptera, by various Carabid, Heteromerous, and Longicorn 

 Coleoptera, and by some Hemiptera ; while certain ants are 

 well imitated by spiders. As regards Coleoptera, mimicry is 

 mainly found within the limits of the order itself — e.g. Cicin- 

 delids by Heteromera and Longicorns, Carabids by Heter- 

 omera, Malacoderms by Longicorns, and Rhynchophora by 

 Longicorns ; but certain Cicindelid and Rhynchophorous beetles 

 are closely copied by Orthoptera, belonging respectively to the 

 genera Condylodeira and Scepastus. Lepidoptera do not seem 

 to find mimickers beyond their own order, unless the case 

 quoted by Haase from E. Hartert, of the resemblance of a large 

 Cicada to the Indian Thaiimantis aliris (Morphinse) be one of 

 actual mimicry. Nor do Diptera appear to be models for 

 imitation, except in the case of the hunting spiders, which 

 mimic the Muscidje they chase ; although the neuropterous 

 Bittaciis certainly bears a strong likeness to Tipula, and may 

 possibly find the advantage of that harmless aspect in approach- 

 ing its prey. It cannot be denied that some of the inter-ordinal 

 mimicries are even more impressive and striking than those so 

 notable among butterflies, the excellence of the superficial dis- 

 guise of general outline, proportion of parts, colouring, and 

 markings being so great as to throw into obscurity the really 

 vast structural discrepancies. Such cases as the imitation of the 

 South American wasps of the genera Polybia and Synccca by 

 moths of the genera Sphecosoina and Myrmecopsis, of the 

 Bornean sand-wasp Mygnimta avicuhis, by the beetle Colo- 

 horrliombiis fasciatipennis ,'^ or of the Philippine tiger-beetle 

 Tricondyla, by the cricket Condylodeira, are absolute marvels 

 of deception, all belonging to that special phase of mimicry 

 where the obvious advantage to the unarmed mimic lies in being 

 mistaken for the armed and formidable model. 



Returning to the general aspects of the subject, it is of im- 

 portance to consider more closely how the evidence stands in 

 relation to {a) persecution by insectivorous foes, {b) possession of 

 malodorous and distasteful juices by certain groups of insects, {c) 

 rejection or avoidance by foes of the insects provided with offensive 

 juices, and {d) loss occasioned to distasteful species by the attacks 

 of young and inexperienced enemies ; for it is admittedly on the 

 co-operation of these factors that the theory of mimicry depends. 



{a) Persecution by Insectivorous Foes. 



As regards the first point, the broad fact of insects generally 

 constituting the food of countless devourers, vertebrate and in- 

 vertebrate, is beyond dispute ; immense and incessant persecu- 

 tion is universally at work. But when we proceed to examine 

 this world-wide persecution more in detail, and to ask in what 

 special directions it works, or what groups or species are the 

 particular prey of certain groups or species of enemies, we very 

 soon discover how little is exactly known. Birds, for instance, 

 are such notorious and apparently indiscriminate insect-eaters, 

 and some of them are so active and demonstrative in their 

 hunting, that it seems but reasonable to regard them as the chief 



1 It should be noted that in the African H. saltnacis and the Malagasy 

 H. dexithea the sexes are alike and non-mimetic, and that therefore these 

 species probably most closely approximate to the primitive appearance of 

 the genus. 



2 See Pryer, Trans. Ent. Soc, 1885, p. 369, pi. x., who in the same 

 place also figures another most striking case from Borneo, in which the 

 hymenopterous Triscolia patricialis is mimicked by the lepidopterous 

 Scolioiiiima insignis. 



NO. 1474, VOL. 57] 



pursuers on the wing of the abundant and defenceless butterflies. 

 Yet in the discussion which followed the reading of Dr. Dixey's 

 last paper already referred to nothing was more noticeable than 

 the very scanty testimony to such persecution on the part of 

 birds that could be brought forward by the very competent well- 

 travelled entomologists present. In fact, the poverty of observed 

 cases of such attack has induced the opinion among some 

 entomologists that birds very rarely chase butterflies at all, and 

 the published expression of this view by Pryer, Skertchley, 

 Piepers, and other experienced collectors cannot be overlooked. 

 But I am persuaded that in this instance, as in so many others 

 where the life-history of animals is concerned, the dearth of 

 evidence is due to the neglect of well-directed and sustained 

 observation. Little can be gained by merely noting such cases 

 as happen to force themselves on the collector's attention ; the 

 collector must resolutely set himself to search out and keep 

 watch upon what really takes place. Considering that there is 

 no record of any naturalist's having seriously taken up the in- 

 vestigation of this matter in the field, I think that very much 

 positive evidence could hardly be expected, and that what has 

 been published goes far in the direction of proving that birds 

 must still be reckoned among the principal enemies of 

 butterflies. 



{b) Possession of Malodorous and Distasteful Juices 

 BY certain Insects. 



The presence of malodorous juices in many insects is a matter 

 of common observation, and is a protective property possessed 

 by several entire groups, especially among the Lepidoptera and 

 Coleoptera. There is abundant evidence as to the prevalence of 

 these secretions, and among the Lepidoptera they are particularly 

 developed in the butterflies of the groups Danainae, Neotropinre, 

 Acrseinae, and Heliconinae, and also in some Papilioninje, 

 as well as in many moths of the groups Agaristidse, Chalcosiidse, 

 Arctiidae, Lithosiidae, &c. The strength of the disagreeable 

 odour emitted is in some species very great ; Seitz, for instance, 

 mentioning that the smell of the South-American Heliconitis 

 besckei and Eiieides aliphera extends over a radius of several 

 paces, and Woodmason and De Niceville testifying to the same 

 effect as regards the Indian Papilio philoxenus and allied forms. 

 When molested many of these offensively-smelling species 

 exude drops of a yellow or whitish fluid which leave on any- 

 thing they touch a stain and odour difficult to remove, as I 

 have experienced in the case of the Mauritian Euplcca euphone, 

 the South -African Danainae and Acraeinae, and various South- 

 African Agaristidae, Glaucopidae, and Arcliidae. 



The origin and manner of acquisition of these unsavoury 

 secretions have yet to be discovered ; the suggestion (so much 

 insisted on by Haase) that these juices are directly derived from 

 those of similar quality in the food-plants of the larvae arising 

 from the long-known circumstance that some of the food-plants 

 of species in the protected groups are of an acrid or poisonous 

 character, such as {e.g.) Asclepiads in the case of many Danainae, 

 and Aristolochia in that of the inedible forms of Papilioninae. 

 No doubt, too, the fact that the unpleasant qualities are very 

 often fully developed in the larvae of the distasteful species — as 

 I have found with Danais chrysippus and various Acraeinae — lends 

 some weight to the suggestion ; but at present nothing ap- 

 proaching sufficient data can be brought forward respecting 

 the actual food plants to which the protected groups, in contrast 

 to the unprotected, are thought to be restricted. It cannot be 

 gainsaid, as Prof. Poulton has pointed out [Proc. Zool. Soc. 

 Land., 1887, pp. 198, &c., and Nature, November 4, 1897, 

 p. 3), that the food-plants of many of the distasteful European 

 moths do not belong to any poisonous or acrid category ; and 

 his own and Mr. Latter's papers on Dicranura vinula alone 

 amply demonstrate what powerful acids can be elaborated by a 

 larva which finds its food in such innocuous plants as poplar and 

 willow. The supposed direct derivation of the nauseous juices 

 from the plants consumed is thus plainly a matter that awaits 

 investigation from both biological and chemical standpoints. 



(c) Avoidance or Rejection of Insects by 

 Insectivorous Animals. 



The avoidance or rejection as food by insectivorous animals 

 of the insects possessing malodorous or distasteful juices no 

 longer rests merely on the negative evidence given by Bates, 

 Wallace, Belt, and other competent observers, to the effect that 

 in nature such distasteful forms are habitually neglected and 

 unmolested ; there is now much positive experimental evidence 



