Part 4

The terms “_mimicry_” and “_mimickers_” have been objected to on the ground that they imply _voluntary action_ on the part of the insects. This appears to me of little importance compared with the advantages of convenience, flexibility, and expressiveness which they undoubtedly possess, especially as the whole theory propounded by the originator of the term in this sense excludes all idea of voluntary action. The only approximately synonymous words, not implying will, are _resemblance_, _similarity_, and _likeness_; and it is evident that none of these can be applied intelligibly under the variety of forms required, and to which Mr. Bates’s expression so readily lends itself in the terms _mimic_, _mimickers_, _mimicry_, _mimicked_. Add to this the inconvenience of changing a term which, from the interest and wide discussion of the subject, must be already very generally understood, and I think it will be admitted that nothing would be gained by altering it, even if a better word were pointed out, which has not yet been done.

We have therefore fifteen species or marked varieties of _Papilio_ which so closely resemble species of other groups in their respective localities, that it is not possible to impute the resemblance to accident. The first two in the list (_Papilio paradoxa_ and _P. Caunus_) are so exactly like _Euplœa Midamus_ and _E. Rhadamanthus_ on the wing, that, although they fly very slowly, I was quite unable to distinguish them. The first is a very interesting case, because the male and female differ considerably, and each mimics the corresponding sex of the _Euplœa_. A new species of _Papilio_ which I discovered in New Guinea resembles _Danais sobrina_, Bd., from the same country, just as _Papilio Macareus_ resembles _Danais Aglaia_ in Malacca, and (according to Dr. Horsfield’s figure) still more closely in Java. The Indian _Papilio Agestor_ closely imitates _Danais Tytia_, which has quite a different style of colouring from the preceding; and the extraordinary _Papilio idæoides_ from the Philippine Islands must, when on the wing, perfectly resemble the _Hestia Leuconoë_ of the same region, as also does the _P. Delessertii_, Guér., imitate an undescribed species of _Hestia_ from Penang. Now in every one of these cases the Papilios are very scarce, while the Danaidæ which they resemble are exceedingly abundant—most of them swarming so as to be a positive nuisance to the collecting entomologist by continually hovering before him when he is in search of newer and more varied captures. Every garden, every roadside, the suburbs of every village are full of them, indicating very clearly that their life is an easy one, and that they are free from persecution by the foes which keep down the population of less favoured races. This superabundant population has been shown by Mr. Bates to be a general characteristic of all American groups and species which are objects of mimicry; and it is interesting to find his observations confirmed by examples on the other side of the globe.

The remarkable genus _Drusilla_, a group of pale-coloured butterflies, more or less adorned with ocellate spots, is also the object of mimicry by three distinct genera (_Melanitis_, _Hyantis_, and _Papilio_). These insects, like the _Danaidæ_, are abundant in individuals, have a very weak and slow flight, and do not seek concealment, or appear to have any means of protection from insectivorous creatures. It is natural to conclude, therefore, that they have some hidden property which saves them from attack; and it is easy to see that when any other insects, by what we call accidental variation, come more or less remotely to resemble them, the latter will share to some extent in their immunity. An extraordinary dimorphic form of a female _Papilio_ has come to resemble the Drusillas sufficiently to be taken for one of that group at a little distance; and it is curious that I captured one of these Papilios in the Aru Islands hovering along the ground, and settling on it occasionally, just as it is the habit of the Drusillas to do. The resemblance in this case is only general; but this form of _Papilio_ varies much, and there is therefore material for natural selection to act upon so as ultimately to produce a copy as exact as in the other cases.

The eastern Papilios allied to _Polydorus Coon_ and _P. Philoxenus_, form a natural section of the genus resembling, in many respects, the _Æneas_-group of South America, which they may be said to represent in the East. Like them, they are forest insects, have a low and weak flight, and in their favourite localities are rather abundant in individuals; and like them, too, they are the objects of mimicry. We may conclude, therefore, that they possess some hidden means of protection, which makes it useful to other insects to be mistaken for them.

The Papilios which resemble them belong to a very distinct section of the genus, in which the sexes differ greatly; and it is those females only which differ most from the males, and which have already been alluded to as exhibiting instances of dimorphism, which resemble species of the other group.

The resemblance of _P. Romulus_ to _P. Hector_ is, in some specimens, very considerable, and has led to the two species being placed to follow each other in the British Museum Catalogues and by Mr. E. Doubleday. I have shown, however, that _P. Romulus_ is probably a dimorphic form of the female _P. Pammon_, and belongs to a distinct section of the genus[9].

Footnote 9:

See Plate II. fig. 6.

The next pair, _P. Theseus_, Cr., and _P. Antiphus_, Fab., have been united as one species both by De Haan and in the British Museum Catalogues. The ordinary variety of _P. Theseus_ found in Java almost as nearly resembles _P. Diphilus_, Esp., of the same country. The most interesting case, however, is the extreme female form of _P. Memnon_ (_P. Achates_, Cr.)[10], which has acquired the general form and markings of _P. Coon_, an insect which differs from the ordinary male _P. Memnon_, as much as any two species differ which can be chosen in this extensive and highly varied genus; and, as if to show that this resemblance is not accidental, but is the result of law, when in India we find a species closely allied to _P. Coon_, but with red instead of yellow spots (_P. Doubledayi_, Wall.), the corresponding variety of _P. Androgeus_ (_P. Achates_, Cram., 182, A, B,) has acquired exactly the same peculiarity of having red spots instead of yellow. Lastly, in the island of Timor, the female of _P. Œnomaus_ (a species allied to _P. Memnon_) resembles so closely _P. Liris_ (one of the _Polydorus_-group), that the two, which were often seen flying together, could only be distinguished by a minute comparison after being captured.

Footnote 10:

See Plate I. fig. 4.

The last six cases of mimicry are especially instructive, because they seem to indicate one of the processes by which dimorphic forms have been produced. When, as in these cases, one sex differs much from the other, and varies greatly itself, it may happen that occasionally individual variations will occur having a distant resemblance to groups which are the objects of mimicry, and which it is therefore advantageous to resemble. Such a variety will have a better chance of preservation; the individuals possessing it will be multiplied; and their accidental likeness to the favoured group will be rendered permanent by hereditary transmission, and, each successive variation which increases the resemblance being preserved, and all variations departing from the favoured type having less chance of preservation, there will in time result those singular cases of two or more isolated and fixed forms bound together by that intimate relationship which constitutes them the sexes of a single species. The reason why the females are more subject to this kind of modification than the males is, probably, that their slower flight, when laden with eggs, and their exposure to attack while in the act of depositing their eggs upon leaves, render it especially advantageous for them to have some additional protection. This they at once obtain by acquiring a resemblance to other species which, from whatever cause, enjoy a comparative immunity from persecution.

This summary of the more interesting phenomena of variation presented by the eastern Papilionidæ is, I think, sufficient to substantiate my position, that the Lepidoptera are a group that offer especial facilities for such inquiries; and it will also show that they have undergone an amount of special adaptive modification rarely equalled among the more highly organized animals. And, among the Lepidoptera, the great and pre-eminently tropical families of Papilionidæ and Danaidæ seem to be those in which complicated adaptations to the surrounding organic and inorganic universe have been most completely developed, offering in this respect a striking analogy to the equally extraordinary, though totally different, adaptations which present themselves in the _Orchideæ_, the only family of plants in which mimicry of other organisms appears to play any important part, and the only one in which striking cases of polymorphism occur; for such we must consider to be the male, female, and hermaphrodite forms of _Catasetum tridentatum_, which differ so greatly in form and structure that they were long considered to belong to three distinct genera.

_Arrangement and Geographical Distribution of the Malayan_ Papilionidæ.

Although the species of Papilionidæ inhabiting the Malayan region are very numerous, they all belong to three out of the nine genera into which the family is divided. One of the remaining genera (_Eurycus_) is restricted to Australia, and another (_Teinopalpus_) to the Himalayan Mountains, while no less than four (_Parnassius_, _Doritis_, _Thais_, and _Sericinus_) are confined to Southern Europe and to the mountain-ranges of the Palæarctic region.

The genera _Ornithoptera_ and _Leptocircus_ are highly characteristic of Malayan entomology, but are uniform in character and of small extent. The genus _Papilio_, on the other hand, presents a great variety of forms, and is so richly represented in the Malay islands, that more than one-fourth of all the known species are found there. It becomes necessary, therefore, to divide this genus into natural groups before we can successfully study its geographical distribution.

Owing principally to Dr. Horsfield’s observations in Java, we are acquainted with a considerable number of the larvæ of Papilios; and these furnish good characters for the primary division of the genus into natural groups. The manner in which the hinder wings are plaited or folded back at the abdominal margin, the size of the anal valves, the structure of the antennæ, and the form of the wings are also of much service, as well as the character of the flight and the style of coloration. Using these characters, I divide the Malayan Papilios into four sections, and seventeen groups, as follows:—

Genus ORNITHOPTERA.

a. _Priamus_-group. Black and green.

b. _Pompeus_-group. Black and yellow.

c. _Brookeanus_-group.

Genus PAPILIO.

A. Larvæ short, thick, with numerous fleshy tubercles; purplish.

a. _Nox_-group. Abdominal fold in ♂ very large; anal valves small, but swollen; antennæ moderate; wings entire, or tailed: includes the Indian _Philoxenus_-group.

b. _Coon_-group. Abdominal fold in ♂ small; anal valves small, but swollen; antennæ moderate; wings tailed.

c. _Polydorus_-group. Abdominal fold in ♂ small, or none; anal valves small or obsolete, hairy; wings tailed or entire.

B. Larvæ with third segment swollen, transversely or obliquely banded; pupa much bent. Imago with abdominal margin in ♂ plaited, but not reflexed; body weak; antennæ long; wings much dilated, often tailed.

d. _Ulysses_-group.

e. _Peranthus_-group.

_Protenor_-group (Indian) is somewhat intermediate between these, and is nearest to the _Nox_-group.

f. _Memnon_-group.

g. _Helenus_-group.

h. _Erectheus_-group.

i. _Pammon_-group.

k. _Demolion_-group.

C. Larvæ subcylindrical, variously coloured. Imago with abdominal margin in ♂ plaited, but not reflexed; body weak; antennæ short, with a thick curved club; wings entire.

l. _Erithonius_-group. Sexes alike, larva and pupa something like those of _P. Demolion_.

m. _Paradoxa_-group. Sexes different.

n. _Dissimilis_-group. Sexes alike; larva bright-coloured; pupa straight, cylindric.

D. Larvæ elongate, attenuate behind, and often bifid, with lateral and oblique pale stripes, green. Imago with the abdominal margin in ♂ reflexed, woolly or hairy within; anal valves small, hairy; antennæ short, stout; body stout.

o. _Macareus_-group. Hind wings entire.

p. _Antiphates_-group. Hind wings much tailed (swallow-tails).

q. _Eurypylus_-group. Hind wings elongate or tailed.

Genus LEPTOCIRCUS.

making, in all, twenty distinct groups of Malayan Papilionidæ.

The first section of the genus _Papilio_ (A) comprises insects which, though differing considerably in structure, have much general resemblance. They all have a weak, low flight, frequent the most luxuriant forest districts, seem to love the shade, and are the objects of mimicry by other Papilios.

Section B consists of weak-bodied, large-winged insects, with an irregular wavering flight, and which, when resting on foliage, often expand the wings, which the species of the other sections rarely or never do. They are the most conspicuous and striking of eastern Butterflies.

Section C consists of much weaker and slower-flying insects, often resembling in their flight, as well as in their colours, species of Danaidæ.

Section D contains the strongest-bodied and most swift-flying of the genus. They love sunlight, and frequent the borders of streams and the edges of puddles, where they gather together in swarms consisting of several species, greedily sucking up the moisture, and, when disturbed, circling round in the air, or flying high and with great strength and rapidity.

In the following Table I have arranged all the Malayan Papilionidæ in what appears to me their most natural succession, and have exhibited their distribution in twenty-one columns of localities, extending from the Malay peninsula, on the north-west, to Woodlark Island, near New Guinea, on the south-east. The double line divides the Indo-Malayan from the Austro-Malayan region; and those islands which form natural zoological groups are connected by brackets.

_Table showing the Distribution of the Malayan_ Papilionidæ.