If, therefore, we accept it as highly probable (if not proved) that the Heliconid? are very greatly protected from attack by their peculiar27 odour and taste, we find it much more easy to understand their chief characteristics — their great abundance, their slow flight, their gaudy28 colours, and the entire absence of protective tints30 on their under surfaces. This property places them somewhat in the position of those curious wingless birds of oceanic islands, the dodo, the apteryx, and the moas, which are with great reason supposed to have lost the power of flight on account of the absence of carnivorous quadrupeds. Our butterflies have been protected in a different way, but quite as effectually; and the result has been that as there has been nothing to escape from, there has been no weeding out of slow flyers, and as there has been nothing to hide from, there has been no extermination31 of the bright-coloured varieties, and no preservation32 of such as tended to assimilate with surrounding objects.
Now let us consider how this kind of protection must act. Tropical insectivorous birds very frequently sit on dead branches of a lofty tree, or on those which overhang forest paths, gazing intently around, and darting33 off at intervals34 to seize an insect at a considerable distance, which they generally return to their station to devour16. If a bird began by capturing the slow-flying, conspicuous Heliconid?, and found them always so disagreeable that it could not eat them, it would after a very few trials leave off catching them at all; and their whole appearance, form, colouring, and mode of flight is so peculiar, that there can be little doubt birds would soon learn to distinguish them at a long distance, and never waste any time in pursuit of them. Under these circumstances, it is evident that any other butterfly of a group which birds were accustomed to devour, would be almost equally well protected by closely resembling a Heliconia externally, as if it acquired also the disagreeable odour; always supposing that there were only a few of them among a great number of the Heliconias. If the birds could not distinguish the two kinds externally, and there were on the average only one eatable among fifty uneatable, they would soon give up seeking for the eatable ones, even if they knew them to exist. If, on the other hand, any particular butterfly of an eatable group acquired the disagreeable taste of the Heliconias while it retained the characteristic form and colouring of its own group, this would be really of no use to it whatever; for the birds would go on catching it among its eatable allies (compared with which it would rarely occur), it would be wounded and disabled, even if rejected, and its increase would thus be as effectually checked as if it were devoured. It is important, therefore, to understand that if any one genus of an extensive family of eatable butterflies were in danger of extermination from insect-eating birds, and if two kinds of variation were going on among them, some individuals possessing a slightly disagreeable taste, others a slight resemblance to the Heliconid?, this latter quality would be much more valuable than the former. The change in flavour would not at all prevent the variety from being captured as before, and it would almost certainly be thoroughly35 disabled before being rejected. The approach in colour and form to the Heliconid?, however, would be at the very first a positive, though perhaps a slight advantage; for although at short distances this variety would be easily distinguished and devoured, yet at a longer distance it might be mistaken for one of the uneatable group, and so be passed by and gain another day’s life, which might in many cases be sufficient for it to lay a quantity of eggs and leave a numerous progeny36, many of which would inherit the peculiarity37 which had been the safeguard of their parent.
Now, this hypothetical case is exactly realized in South America. Among the white butterflies forming the family Pierid? (many of which do not greatly differ in appearance from our own cabbage butterflies) is a genus of rather small size (Leptalis), some species of which are white like their allies, while the larger number exactly resemble the Heliconid? in the form and colouring of the wings. It must always be remembered that these two families are as absolutely distinguished from each other by structural38 characters as are the carnivora and the ruminants among quadrupeds, and that an entomologist can always distinguish the one from the other by the structure of the feet, just as certainly as a zoologist39 can tell a bear from a buffalo40 by the skull41 or by a tooth. Yet the resemblance of a species of the one family to another species in the other family was often so great, that both Mr. Bates and myself were many times deceived at the time of capture, and did not discover the distinctness of the two insects till a closer examination detected their essential differences. During his residence of eleven years in the Amazon valley, Mr. Bates found a number of species or varieties of Leptalis, each of which was a more or less exact copy of one of the Heliconid? of the district it inhabited; and the results of his observations are embodied42 in a paper published in the Linnean Transactions, in which he first explained the phenomena43 of “mimicry” as the result of natural selection, and showed its identity in cause and purpose with protective resemblance to vegetable or inorganic44 forms.
The imitation of the Heliconid? by the Leptalides is carried out to a wonderful degree in form as well as in colouring. The wings have become elongated45 to the same extent, and the antenn? and abdomen46 have both become lengthened47, to correspond with the unusual condition in which they exist in the former family. In colouration there are several types in the different genera of Heliconid?. The genus Mechanitis is generally of a rich semi-transparent48 brown, banded with black and yellow; Methona is of large size, the wings transparent like horn, and with black transverse bands; while the delicate Ithomias are all more or less transparent, with black veins49 and borders, and often with marginal and transverse bands of orange red. These different forms are all copied by the various species of Leptalis, every band and spot and tint29 of colour, and the various degrees of transparency, being exactly reproduced. As if to derive50 all the benefit possible from this protective mimicry, the habits have become so modified that the Leptalides generally frequent the very same spots as their models, and have the same mode of flight; and as they are always very scarce (Mr. Bates estimating their numbers at about one to a thousand of the group they resemble), there is hardly a possibility of their being found out by their enemies. It is also very remarkable that in almost every case the particular Ithomias and other species of Heliconid? which they resemble, are noted51 as being very common species, swarming52 in individuals, and found over a wide range of country. This indicates antiquity53 and permanence in the species, and is exactly the condition most essential both to aid in the development of the resemblance, and to increase its utility.
But the Leptalides are not the only insects who have prolonged their existence by imitating the great protected group of Heliconid?; — a genus of quite another family of most lovely small American butterflies, the Erycinid?, and three genera of diurnal54 moths, also present species which often mimic1 the same dominant55 forms, so that some, as Ithomia ilerdina of St. Paulo, for instance, have flying with them a few individuals of three widely different insects, which are yet disguised with exactly the same form, colour, and markings, so as to be quite undistinguishable when upon the wing. Again, the Heliconid? are not the only group that are imitated, although they are the most frequent models. The black and red group of South American Papilios, and the handsome Erycinian genus Stalachtis, have also a few who copy them; but this fact offers no difficulty, since these two groups are almost as dominant as the Heliconid?. They both fly very slowly, they are both conspicuously56 coloured, and they both abound57 in individuals; so that there is every reason to believe that they possess a protection of a similar kind to the Heliconid?, and that it is therefore equally an advantage to other insects to be mistaken for them. There is also another extraordinary fact that we are not yet in a position clearly to comprehend: some groups of the Heliconid? themselves mimic other groups. Species of Heliconia mimic Mechanitis, and every species of Napeogenes mimics58 some other Heliconideous butterfly. This would seem to indicate that the distasteful secretion59 is not produced alike by all members of the family, and that where it is deficient60 protective imitation comes into play. It is this, perhaps, that has caused such a general resemblance among the Heliconid?, such a uniformity of type with great diversity of colouring, since any aberration61 causing an insect to cease to look like one of the family would inevitably62 lead to its being attacked, wounded, and exterminated63, even although it was not eatable.
In other parts of the world an exactly parallel series of facts have been observed. The Danaid? and the Acr?id? of the Old World tropics form in fact one great group with the Heliconid?. They have the same general form, structure, and habits: they possess the same protective odour, and are equally abundant in individuals, although not so varied in colour, blue and white spots on a black ground being the most general pattern. The insects which mimic these are chiefly Papilios, and Diadema, a genus allied64 to our peacock and tortoiseshell butterflies. In tropical Africa there is a peculiar group of the genus Danais, characterized by dark-brown and bluish-white colours, arranged in bands or stripes. One of these, Danais niavius, is exactly imitated both by Papilio hippocoon and by Diadema anthedon; another, Danais echeria, by Papilio cenea; and in Natal65 a variety of the Danais is found having a white spot at the tip of wings, accompanied by a variety of the Papilio bearing a corresponding white spot. Acr?a gea is copied in its very peculiar style of colouration by the female of Papilio cynorta, by Panop?a hirce, and by the female of Elymnias phegea. Acr?a euryta of Calabar has a female variety of Panopea hirce from the same place which exactly copies it; and Mr. Trimen, in his paper on Mimetic Analogies among African Butterflies, published in the Transactions of the Linn?an Society for 1868, gives a list of no less than sixteen species and varieties of Diadema and its allies, and ten of Papilio, which in their colour and markings are perfect mimics of species or varieties of Danais or Acr?a which inhabit the same districts.
Passing on to India, we have Danais tytia, a butterfly with semi-transparent bluish wings and a border of rich reddish brown. This remarkable style of colouring is exactly reproduced in Papilio agestor and in Diadema nama, and all three insects not unfrequently come together in collections made at Darjeeling. In the Philippine Islands the large and curious Idea leucon?e with its semi-transparent white wings, veined and spotted66 with black, is copied by the rare Papilio id?oides from the same islands.
In the Malay archipelago the very common and beautiful Euploea midamus is so exactly mimicked67 by two rare Papilios (P. paradoxa and P. ?nigma) that I generally caught them under the impression that they were the more common species; and the equally common and even more beautiful Euploea rhadamanthus, with its pure white bands and spots on a ground of glossy68 blue and black, is reproduced in the Papilio caunus. Here also there are species of Diadema imitating the same group in two or three instances; but we shall have to adduce these further on in connexion with another branch of the subject.
It has been already mentioned that in South America there is a group of Papilios which have all the characteristics of a protected race, and whose peculiar colours and markings are imitated by other butterflies not so protected. There is just such a group also in the East, having very similar colours and the same habits, and these also are mimicked by other species in the same genus not closely allied to them, and also by a few of other families. Papilio hector, a common Indian butterfly of a rich black colour spotted with crimson69, is so closely copied by Papilio romulus, that the latter insect has been thought to be its female. A close examination shows, however, that it is essentially70 different, and belongs to another section of the genus. Papilio antiphus and P. diphilus, black swallow-tailed butterflies with cream-coloured spots, are so well imitated by varieties of P. theseus, that several writers have classed them as the same species. Papilio liris, found only in the island of Timor, is accompanied there by P. ?nomaus, the female of which so exactly resembles it that they can hardly be separated in the cabinet, and on the wing are quite undistinguishable. But one of the most curious cases is the fine yellow-spotted Papilio c?on, which is unmistakeably imitated by the female tailed form of Papilio memnon. These are both from Sumatra; but in North India P. c?on is replaced by another species, which has been named P. doubledayi, having red spots instead of yellow; and in the same district the corresponding female tailed form of Papilio androgeus, sometimes considered a variety of P. memnon, is similarly red-spotted. Mr. Westwood has described some curious day-flying moths (Epicopeia) from North India, which have the form and colour of Papilios of this section, and two of these are very good imitations of Papilio polydorus and Papilio varuna, also from North India.
Almost all these cases of mimicry are from the tropics, where the forms of life are more abundant, and where insect development especially is of unchecked luxuriance; but there are also one or two instances in temperate71 regions. In North America, the large and handsome red and black butterfly Danais erippus is very common; and the same country is inhabited by Limenitis archippus, which closely resembles the Danais, while it differs entirely72 from every species of its own genus.
The only case of probable mimicry in our own country is the following:— A very common white moth (Spilosoma menthastri) was found by Mr. Stainton to be rejected by young turkeys among hundreds of other moths on which they greedily fed. Each bird in succession took hold of this moth and threw it down again, as if too nasty to eat. Mr. Jenner Weir73 also found that this moth was refused by the Bullfinch, Chaffinch, Yellow Hammer, and Red Bunting, but eaten after much hesitation74 by the Robin75. We may therefore fairly conclude that this species would be disagreeable to many other birds, and would thus have an immunity from attack, which may be the cause of its great abundance and of its conspicuous white colour. Now it is a curious thing that there is another moth, Diaphora mendica, which appears about the same time, and whose female only is white. It is about the same size as Spilosoma menthastri, and sufficiently76 resembles it in the dusk, and this moth is much less common. It seems very probable, therefore, that these species stand in the same relation to each other as the mimicking77 butterflies of various families do to the Heliconid? and Danaid?. It would be very interesting to experiment on all white moths, to ascertain78 if those which are most common are generally rejected by birds. It may be anticipated that they would be so, because white is the most conspicuous of all colours for nocturnal insects, and had they not some other protection would certainly be very injurious to them.
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1
mimic
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| v.模仿，戏弄；n.模仿他人言行的人 | |
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mimicry
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| n.（生物）拟态，模仿 | |
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remarkable
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| adj.显著的，异常的，非凡的，值得注意的 | |
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distinguished
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| adj.卓越的，杰出的，著名的 | |
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elongate
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| v.拉长，伸长，延长 | |
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varied
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| adj.多样的，多变化的 | |
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conspicuous
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| adj.明眼的，惹人注目的；炫耀的，摆阔气的 | |
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persecuted
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| （尤指宗教或政治信仰的）迫害(~sb. for sth.)( persecute的过去式和过去分词 )； 烦扰，困扰或骚扰某人 | |
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repose
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| v.(使)休息；n.安息 | |
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twigs
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| 细枝，嫩枝( twig的名词复数 ) | |
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fully
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| adv.完全地，全部地，彻底地；充分地 | |
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pungent
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| adj.（气味、味道）刺激性的，辛辣的；尖锐的 | |
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pervade
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| v.弥漫，遍及，充满，渗透，漫延 | |
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exudes
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| v.缓慢流出，渗出，分泌出( exude的第三人称单数 )；流露出对（某物）的神态或感情 | |
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immunity
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| n.优惠；免除；豁免，豁免权 | |
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devour
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| v.吞没；贪婪地注视或谛听，贪读；使着迷 | |
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devoured
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| 吞没( devour的过去式和过去分词 )； 耗尽； 津津有味地看； 狼吞虎咽地吃光 | |
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moth
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| n.蛾，蛀虫 | |
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moths
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| n.蛾( moth的名词复数 ) | |
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amassed
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| v.积累，积聚( amass的过去式和过去分词 ) | |
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caterpillars
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| n.毛虫( caterpillar的名词复数 )；履带 | |
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dread
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| vt.担忧，忧虑；惧怕，不敢；n.担忧，畏惧 | |
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23
catching
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| adj.易传染的，有魅力的，迷人的，接住 | |
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molested
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| v.骚扰( molest的过去式和过去分词 )；干扰；调戏；猥亵 | |
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lizards
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| n.蜥蜴( lizard的名词复数 ) | |
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pounce
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| n.猛扑；v.猛扑，突然袭击，欣然同意 | |
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peculiar
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| adj.古怪的，异常的；特殊的，特有的 | |
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gaudy
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| adj.华而不实的；俗丽的 | |
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29
tint
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| n.淡色，浅色；染发剂；vt.着以淡淡的颜色 | |
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tints
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| 色彩( tint的名词复数 )； 带白的颜色； （淡色）染发剂； 痕迹 | |
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extermination
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| n.消灭，根绝 | |
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preservation
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| n.保护，维护，保存，保留，保持 | |
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darting
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| v.投掷，投射( dart的现在分词 )；向前冲，飞奔 | |
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intervals
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| n.[军事]间隔( interval的名词复数 )；间隔时间；[数学]区间；（戏剧、电影或音乐会的）幕间休息 | |
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thoroughly
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| adv.完全地，彻底地，十足地 | |
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progeny
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| n.后代，子孙；结果 | |
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peculiarity
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| n.独特性，特色；特殊的东西；怪癖 | |
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structural
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| adj.构造的，组织的，建筑（用）的 | |
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zoologist
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| n.动物学家 | |
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40
buffalo
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| n.(北美)野牛；(亚洲)水牛 | |
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skull
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| n.头骨；颅骨 | |
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42
embodied
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| v.表现( embody的过去式和过去分词 )；象征；包括；包含 | |
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phenomena
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| n.现象 | |
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inorganic
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| adj.无生物的；无机的 | |
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45
elongated
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| v.延长，加长( elongate的过去式和过去分词 ) | |
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46
abdomen
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| n.腹，下腹(胸部到腿部的部分) | |
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47
lengthened
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| （时间或空间）延长，伸长( lengthen的过去式和过去分词 ) | |
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transparent
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| adj.明显的，无疑的；透明的 | |
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veins
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| n.纹理；矿脉( vein的名词复数 )；静脉；叶脉；纹理 | |
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50
derive
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| v.取得；导出；引申；来自；源自；出自 | |
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51
noted
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| adj.著名的，知名的 | |
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52
swarming
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| 密集( swarm的现在分词 )； 云集； 成群地移动； 蜜蜂或其他飞行昆虫成群地飞来飞去 | |
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53
antiquity
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| n.古老；高龄；古物，古迹 | |
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diurnal
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| adj.白天的，每日的 | |
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dominant
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| adj.支配的，统治的；占优势的；显性的；n.主因，要素，主要的人(或物)；显性基因 | |
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56
conspicuously
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| ad.明显地，惹人注目地 | |
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abound
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| vi.大量存在；(in，with)充满，富于 | |
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58
mimics
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| n.模仿名人言行的娱乐演员，滑稽剧演员( mimic的名词复数 )；善于模仿的人或物v.（尤指为了逗乐而）模仿( mimic的第三人称单数 )；酷似 | |
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secretion
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| n.分泌 | |
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deficient
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| adj.不足的，不充份的，有缺陷的 | |
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aberration
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| n.离开正路，脱离常规，色差 | |
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inevitably
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| adv.不可避免地；必然发生地 | |
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exterminated
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| v.消灭，根绝( exterminate的过去式和过去分词 ) | |
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64
allied
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| adj.协约国的；同盟国的 | |
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natal
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| adj.出生的，先天的 | |
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spotted
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| adj.有斑点的，斑纹的，弄污了的 | |
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mimicked
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| v.（尤指为了逗乐而）模仿( mimic的过去式和过去分词 )；酷似 | |
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glossy
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| adj.平滑的；有光泽的 | |
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crimson
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| n./adj.深(绯)红色(的)；vi.脸变绯红色 | |
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essentially
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| adv.本质上，实质上，基本上 | |
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temperate
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| adj.温和的，温带的，自我克制的，不过分的 | |
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entirely
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| ad.全部地，完整地；完全地，彻底地 | |
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73
weir
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| n.堰堤，拦河坝 | |
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74
hesitation
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| n.犹豫，踌躇 | |
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75
robin
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| n.知更鸟，红襟鸟 | |
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76
sufficiently
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| adv.足够地，充分地 | |
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77
mimicking
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| v.（尤指为了逗乐而）模仿( mimic的现在分词 )；酷似 | |
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78
ascertain
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| vt.发现，确定，查明，弄清 | |
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