OLD-WORLD MIMICS
The earlier naturalists who studied butterflies made use of colour and
pattern very largely in arranging and classifying their specimens. Insects
shewing the same features in these respects were generally placed together
without further question, especially if they were known to come from the
same locality. In looking through old collections of butterflies from the
tropics it is not infrequent to find that the collector was deceived by a
mimetic likeness into placing model and mimic together. During the last
century, however, more attention was paid to the anatomy of butterflies,
with the result that their classification was placed upon a basis of
structure. As in all work of the sort certain features are selected, partly
owing to their constancy and partly for their convenience, the insects
being arranged according as to whether they present these features or not.
Everybody knows that the butterflies as a group are separated from the
moths on the ground that their antennae are club shaped at the end, while
those of the moth are generally filamentary and taper to a fine point. {19}
[Illustration: Figs. 1-8. Terminal portion of front legs of butterflies
belonging to different families. (After Eltringham.)]
1. _Hypolimnas misippus_, [F] (Nymphalidae).
2. " " [M] ( " ).
3. _Abisara savitri_, [F] (Erycinidae).
4. " " [M] ( " ).
5. _Lycaena icarus_, [F] (Lycaenidae).
6. _Cupido zoë_, [M] ( " ).
7. _Ganoris rapae_, [M] (Pieridae).
8. _Papilio echerioides_, [F] (Papilionidae).
{20} The butterflies themselves may be subdivided into five main groups or
families[10] according to the structure of the first of their three pairs
of legs. In the Papilionidae or "swallow-tails," the first pair of legs is
well developed in both sexes (Fig. 8). In the Pieridae or "whites," the
front legs are also similar in both sexes, but the claws are bifid and a
median process, the empodium, is found between them (Fig. 7). In the
remaining three families the front legs differ in the two sexes. The
females of the Lycaenidae or "blues" have well-developed front legs in
which the tarsus is terminated by definite claws (Fig. 5), whereas in the
males the terminal part of the leg, or tarsus, is unjointed and furnished
with but a single small claw (Fig. 6). This reduction of the front legs has
gone somewhat further in the Erycinidae (Figs. 3 and 4), a family
consisting for the most part of rather small butterflies and specially
characteristic of South America. In the great family of the Nymphalidae the
reduction of the front legs is well marked in both sexes. Not only are they
much smaller than in the other groups, but claws are lacking in the female
as well as in the male (Figs. 1 and 2).
Though the structure of the fore limbs is the character specially chosen
for separating these different families from one another, it is of course
understood that they differ from one another in various other distinctive
features. The chrysalis of the Nymphalidae for example hangs head downwards
suspended by the {21} tail, whereas in the Pieridae and Papilionidae
metamorphosis takes place with the chrysalis attached by the tail but
supported also by a fine girdle of silk round the middle so that the head
is uppermost. The larvae also afford characters by which some of the
families may be distinguished--those of the Papilionidae for example having
a process on the back which can be extruded or retracted.
Owing to the great size of the family of the Nymphalidae, in which the
number of species approaches 5000, it is convenient to deal with the eight
sub-groups into which it has been divided. The characters serving to mark
off the sub-groups from one another are various. Sometimes it is the
minuter structure of the tarsus, at others the form of the caterpillar or
the chrysalis, at others the arrangement of the nervures that form the
skeleton of the wing. Into these systematic details, however, we need not
enter more fully here[11]. What is important from the standpoint of mimicry
is that these divisions, made solely on anatomical structure, correspond
closely with the separation of models from mimics. Of the eight
sub-families into which the Nymphalidae are divided four, viz. the
Danainae, Acraeinae, Heliconinae, and Ithomiinae, provide models and some,
but far fewer, mimics; two, the Satyrinae and Nymphalinae, provide many
mimics and but few models, while two groups, the Morphinae and Brassolinae,
practically do not enter into the mimicry story. {22}
Simple mimicry, explicable, at any rate in theory, on the lines laid down
by Bates, is a phenomenon of not infrequent occurrence in tropical
countries, though rare in more temperate lands. In each of the three great
divisions of the tropical world we find certain groups of butterflies
serving as models, and being mimicked by butterflies belonging as a rule to
quite different groups. Speaking generally the models of any given region
are confined to a few groups, while the mimics are drawn from a greater
number. In Asia the principal models belong to the Danaines, the
Euploeines, and to a group of swallow-tails which from the fact that their
larvae feed on the poisonous _Aristolochia_ plant are generally
distinguished as the "Poison-eaters," or _Pharmacophagus_ group. Of these
the Danaines and Euploeines are closely related and have much in common.
They are usually butterflies of medium size, of rather flimsy build and
with a somewhat slow and flaunting flight. In spite, however, of their
slight build they are toughly made and very tenacious of life. Most
butterflies are easily killed by simply nipping the thorax. There is a
slight crack and the fly never recovers. But the collector who treats a
Danaid in a way that would easily kill most butterflies is as likely as not
many hours after to find it still alive in his collecting box or in the
paper to which it may have been transferred when caught. They give one the
impression of being tougher and more "rubbery" in consistence than the
majority of Lepidoptera. Moreover, the juices of their bodies seem {23} to
be more oily and less easily dried up. In general colour scheme they vary a
great deal. Some, such as _Danais chrysippus_ (Pl. IV, fig. 1), are
conspicuous with their bright fulvous-brown ground colour and the sharp
white markings on the black tips of their fore wings. Others again such as
_Danais septentrionis_ (Pl. I, fig. 3), with a dark network of lines on a
pale greenish ground, are not nearly so conspicuous. Of the Euploeines some
have a beautiful deep blue metallic lustre (cf. Pl. II, fig. 4), though
many are of a plain sombre brown relieved only by an inconspicuous border
of lighter markings (cf. Pl. I, fig. 10).
Both Danaines and Euploeines serve as models for a great variety of species
belonging to different groups. _Danais septentrionis_ (Pl. I, fig. 3) is a
very abundant species in India and Ceylon, and in the same region there are
several other very similar species. Flying with them in Northern India are
two species of _Papilio_, _P. macareus_ and _P. xenocles_ (Pl. I, fig. 4),
which resemble these Danaids fairly closely. In Southern India and Ceylon
one of the two forms of _Papilio clytia_ (Pl. I, fig. 7) is also regarded
as a mimic of these Danaids. In the same part of the world there is a
Pierine of the genus _Pareronia_, whose female is very like these Danaines
on the upper surface (Pl. I, fig. 1). The male of this Pierine is quite
distinct from the female (Pl. I, fig. 2).
The common _Danais chrysippus_ (Pl. IV, fig. 1), found in this region, has
been described as probably the most abundant butterfly in the world, and
serves {24} as a model for several species belonging to different groups.
It and its mimics will, however, be described in more detail later on.
Mention must also be made of the striking case of the Danaid, _Caduga
tytia_ and its Papilionine mimic _P. agestor_ from Sikkim (Pl. II, figs. 2
and 3). In both species the fore wings are pale blue broken by black; while
the hind wings are pale with a deep outer border of rusty red. Not only in
colour but also in shape the swallow-tail bears a remarkable resemblance to
the Danaid. _C. tytia_ is also mimicked by a rare Nymphaline _Neptis
imitans_, which exhibits the same striking colour scheme so very different
from that of most of its allies.
No less remarkable are some of the cases in which the Euploeines serve as
models. _E. rhadamanthus_, for example, is mimicked by the scarce _Papilio
mendax_, and a glance at Figs. 8 and 9 on Plate II shews how well this
butterfly deserves its name. _Euploea rhadamanthus_ also serves as a model
for one of the several forms of female of the Nymphaline species _Euripus
halitherses_. In some Euploeines the sexes are different in appearance--a
somewhat unusual thing among butterflies serving as models in cases of
mimetic resemblance. Such a difference is found in _Euploea mulciber_, the
male being predominantly brown with a beautiful deep blue suffusion, while
the female is a rather lighter insect with less of the blue suffusion and
with hind wings streaked with lighter markings (Pl. II, figs. 4 and 5). It
is interesting to find that _Elymnias malelas_, a Satyrid which mimics this
species, {25} shews a similar difference in the two sexes (Pl. II, figs. 6
and 7).
It is remarkable that similar sexual difference is also shewn by the rare
_Papilio paradoxus_, the two sexes here again mimicking respectively the
two sexes of _Euploea mulciber_.
Many of the Euploeines, more especially those from Southern India and
Ceylon, lack the blue suffusion, and are sombre brown insects somewhat
relieved by lighter markings along the hinder border of the hind wings.
_Euploea core_ (Pl. I, fig. 10), a very common insect, is typical of this
group. A similar coloration is found in one of the forms of _Papilio
clytia_ (Pl. I, fig. 8) from the same region as well as in the female of
the Nymphaline species _Hypolimnas bolina_ (Pl. I, fig. 6). The male of
this last species (Pl. I, fig. 5) is quite unlike its female, but is not
unlike the male of the allied species, _H. misippus_, which it resembles in
the very dark wings each with a white patch in the centre, the junction of
light and dark being in each case marked by a beautiful purple-blue
suffusion. There is also a species of _Elymnias_ (_E. singhala_) in this
part of the world which in general colour scheme is not widely dissimilar
from these brown Euploeas (Pl. I, fig. 9).
The third main group of models characteristic of this region belongs to the
Papilionidae. It was pointed out by Haase some 20 years ago that this great
family falls into three definite sections, separable on anatomical grounds
(see Appendix II). One of these sections he termed the _Pharmacophagus_ or
"poison-eating" {26} group owing to the fact that the larvae feed on the
poisonous climbing plants of the genus _Aristolochia_. It is from this
group that all Papilios which serve as models are drawn. No mimics of other
unpalatable groups such as Danaines are to be found among the Oriental
Poison-eaters. In the other two sections of the genus mimics are not
infrequent (cf. Appendix II), though probably none of them serve as models.
To the Pharmacophagus group belong the most gorgeous insects of
Indo-Malaya--the magnificent Ornithoptera, largest and most splendid of
butterflies. It is not a large proportion of the members of the group which
serve as models, and these on the whole are among the smaller and less
conspicuous forms. In all cases the mimic, when a butterfly, belongs to the
_Papilio_ section of the three sections into which Haase divided the family
(cf. Appendix II). _Papilio aristolochiae_ (Pl. V, fig. 5), for example, is
mimicked by a female form of _Papilio polytes_, and the geographical
varieties of this widely spread model are generally closely paralleled by
those of the equally wide spread mimic. For both forms range from Western
India across to Eastern China. Another poison-eater, _P. coon_, provides a
model for one of the females of the common _P. memnon_. It is curious that
in those species of the poison-eaters which serve as models the sexes are
practically identical in pattern, and are mimicked by certain females only
of the other two Papilio groups, whereas in the Ornithoptera, which also
belong to the poison-eaters, the difference between the sexes is
exceedingly striking. {27}
Though the Pharmacophagus Papilios are mimicked only by other Papilios
among butterflies they may serve occasionally as models for certain of the
larger day-flying moths. _Papilio polyxenus_, for example, is mimicked not
only by the unprotected _P. bootes_ but also by the moth _Epicopeia
polydora_ (Pl. III, figs. 5 and 6). Like the butterfly the _Epicopeia_,
which is comparatively rare, has the white patch and the outer border of
red marginal spots on the hind wing. Though it is apparently unable to
provide itself with an orthodox tail it nevertheless makes a creditable
attempt at one. There are several other cases of mimetic resemblance
between day-flying moths and Pharmacophagus swallow-tails--the latter in
each case serving as the model. Rarely it may happen that the rôle of
butterfly and moth is reversed, and the butterfly becomes the mimic. A very
remarkable instance of this is found in New Guinea where the rare _Papilio
laglaizei_ mimics the common day-flying moth _Alcidis agathyrsus_. Viewed
from above the resemblance is sufficiently striking (Pl. III, figs. 1 and
2), but the most wonderful feature concerns the underneath. The ventral
half of the moth's abdomen is coloured brilliant orange. When the wings are
folded back they cover and hide from sight only the dorsal part of the
abdomen, so that in this position the orange neutral surface is
conspicuous. When, however, the wings of the butterfly are folded they
conceal the whole of the abdomen. But the butterfly has developed on each
hind wing itself a bright orange patch in such a position that when the
{28} wings are folded back the orange patch lies over the sides of the
abdomen. In this way is simulated the brilliant abdomen of the moth by a
butterfly, in which, as in its relations, this part is of a dark and sombre
hue.
A few models are also provided in the Oriental region by the genus
_Delias_, which belongs to the Pierines. A common form, _Delias eucharis_,
is white above but the under surface of the hind wings is conspicuous with
yellow and scarlet (Pl. II, fig. 1). It has been suggested that this
species serves as a model for another and closely allied Pierine,
_Prioneris sita_, a species distinctly scarcer than the _Delias_. There is
some evidence that the latter is distasteful (cf. p. 115), but nothing is
known of the _Prioneris_ in this respect. Other species of _Delias_ are
said to function as models for certain day-flying moths belonging to the
family Chalcosiidae, which may bear a close resemblance to them. In certain
cases it may happen that the moth is more abundant than the Pierine that it
resembles[12].
Tropical Africa is probably more wealthy in mimetic analogies than
Indo-Malaya, and the African cases have recently been gathered together by
Eltringham in a large and beautifully illustrated memoir[13]. The principal
models of the region are furnished by the Danainae and the allied group of
the Acraeinae. Of the Danaines one well-known model, _Danais chrysippus_,
{29} is common to Africa and to Indo-Malaya. Common also to the two regions
are the mimics, _Argynnis hyperbius_ and _Hypolimnas misippus_ (cf. Pl. IV,
figs. 3 and 7). The case of the last named is peculiarly interesting
because it presents well-marked varieties which can be paralleled by
similar ones in _D. chrysippus_. In addition to the typical form with the
dark tipped fore wing relieved by a white bar there is in each species a
form uniformly brown, lacking both the dark tip and the white bar of the
fore wing. There is also another form in the two species in which the hind
wing is almost white instead of the usual brown shade. In both species,
moreover, the white hind wing may be associated either with the uniformly
brown fore wing or with the typical form. There is also another common
African butterfly, _Acraea encedon_, in which these different patterns are
closely paralleled (cf. Pl. IX). Several other species of butterflies and a
few diurnal moths bear a more or less close resemblance to _D. chrysippus_.
Danaine butterflies with the dark interlacing fines on a pale greenish-blue
ground, so characteristic of the Oriental region, are represented in Africa
by the species _Danais petiverana_ (Pl. VI, fig. 1) ranging across the
continent from Sierra Leone to British East Africa. A common Papilio, _P.
leonidas_ (Pl. VI, fig. 2) has a similar extensive range, and has been
regarded as a mimic of the Danaine. In S. Africa _P. leonidas_ is
represented by the variety _brasidas_ in which the white spots are reduced
and the blue-green ground is lacking. _Brasidas_ bears a strong resemblance
to the tropical {30} Danaine _Amauris hyalites_ (Pl. VI, fig. 3) of which
it has been regarded as a mimic. It must however be added that it is only
over a small part of their respective ranges, viz. in Angola, that the two
species are to be met with together.
The butterflies belonging to the genus _Amauris_ are among the most
abundant and characteristic Danaine models of Africa. Some of the black and
white species such as _A. niavius_ (Pl. VIII, fig. 6) are conspicuous
insects in a cabinet. Others again, such as _A. echeria_ (Pl. VIII, fig.
7), are relatively sombre-looking forms. Among the best known mimics of the
genus is a species of _Hypolimnas_[14]--_H. dubius_. This interesting form
is polymorphic and mimics different species of _Amauris_. The variety
_wahlbergi_, for example, is very like _A. niavius_, while _mima_ strongly
resembles _A. echeria_ (Pl. VIII, figs. 8 and 9). It was at one time
supposed that these two varieties of _Hypolimnas dubius_ were different
species and the matter was only definitely settled when the two forms were
bred from the eggs of the same female. Other mimics of _Amauris_ are found
among the Papilios and the Nymphaline genus _Pseudacraea_.
But among all the mimics of Danaines in Africa and elsewhere _Papilio
dardanus_ is pre-eminent, and has been described by more than one writer as
the most important case of mimicry in existence. Not only does it shew
remarkable resemblances to various {31} Danaids, but it presents features
of such peculiar interest that it must be considered in more detail.
_Papilio dardanus_ in its various sub-races is spread over nearly all the
African continent south of the Sahara. Over all this area the male, save
for relatively small differences, remains unchanged--a lemon-yellow insect,
tailed, and with black markings on fore and hind wings (Pl. VIII, fig. 1).
The female, however, exhibits an extraordinary range of variation. In South
Africa she appears in three guises, (1) the _cenea_ form resembling
_Amauris echeria_, (2) the _hippocoon_ form like _Amauris niavius_, and (3)
the _trophonius_ form which is a close mimic of the common _Danais
chrysippus_[15]. Except that _cenea_ does not occur on the West Coast these
three forms of female are found over almost all the great continental range
of _dardanus_ and its geographical races. Northwards in the latitude of
Victoria Nyanza occurs a distinct form of female, _planemoides_, which
bears a remarkable resemblance to the common and distasteful _Planema
poggei_, and is found only where the latter is abundant. All of these four
forms are close mimics of a common Danaine or Acraeine model. Other forms
of female, however, are known, of which two, _dionysus_ and _trimeni_, are
sufficiently distinct and constant to have acquired special names.
_Dionysus_ may be said to unite the fore wing of the _hippocoon_ form with
the hind wing of the _trophonius_ form, except that the colour of the last
part is yellow instead of {32} bright brown. It is a western form and is
unlike any model. _Trimeni_ also is unlike any model but is of peculiar
interest in that it is much more like the male with its pale creamy-yellow
colour and the lesser development of black scales than occurs in most of
the forms of female. At the same time the general arrangement of the darker
markings is on the whole similar to that in the _hippocoon_ and in the
_trophonius_ form. _Trimeni_ is found on the Kikuyu Escarpment, near Mt
Kenia, along with the four mimicking forms.
Continental Africa, south of the equator, has produced no female similar to
the male. But in Abyssinia is found another state of things. Here, so far
as is known, occur three forms, all tailed, of which one is similar in
general colour and pattern to the male, while the other two, _niavioides_
and _ruspina_[16], resemble respectively a tailed _hippocoon_ and a tailed
_trophonius_. Lastly we have to record that _Papilio dardanus_ is also
found as the geographical race _humbloti_ on Comoro Island, and as
_meriones_ on Madagascar. In both forms the females are tailed, and
resemble the males.
From this long series of facts it is concluded that the male of _P.
dardanus_ represents the original form of both sexes. On the islands of
Comoro and Madagascar this state of things still survives. But it is
supposed that on the African continent existed enemies which persecuted the
species more than on the islands {33} and encouraged the development of
mimetic forms in the female. The original female still lingers in Abyssinia
though it is now accompanied by the two mimetic forms _niavioides_ and
_ruspina_. Over the rest of the area occupied by _dardanus_ the females are
always tailless and, with the exception of _trimeni_ and _dionysus_,
wonderfully close mimics. _Trimeni_, the intermediate form, provides the
clue to the way in which the mimetic females have been derived from the
male, viz. by the prolongation across the fore wing of the dark costal bar
already found in the females of the Madagascar and Abyssinian races, by the
deepening of the dark edging to the wings, and by the loss of the tail.
Through the gradual accumulation of small variations _trimeni_ came from
the male-like female, and by further gradual accumulation of small
favourable variations the mimetic forms came from _trimeni_. South of the
equator the male-like form and the intermediate _trimeni_ have disappeared
owing to the stringency of selection being greater. Moreover the likeness
of mimic to model is closer than in the north, a further proof of the
greater stringency of natural selection in these parts. Such in brief is
the explanation in terms of mimicry of the remarkable and complex case of
_dardanus_.
Although the Euploeinae are not represented on the African continent, it is
the headquarters of another distasteful family of butterflies--the
Acraeinae--which is but sparingly represented in the Oriental region[17].
{34} Of smaller size than the Danaines they are characterised, like this
group, by their tenacity of life and by the presumably distasteful
character of their body juices. They are said also to possess an offensive
odour apparently exuded through the thorax. The majority of the members of
the group fall into the two genera _Acraea_ and _Planema_. Species of
Acraea are on the whole characterised by their general bright red-brown
colour and by the conspicuous black spots on both fore and hind wings. A
typical Acraeine pattern is that of _Acraea egina_ (Pl. VI, fig. 7) which
is mimicked remarkably closely by the Nymphaline _Pseudacraea boisduvali_
and by the Swallow-tail _Papilio ridleyanus_ (Pl. VI, figs. 5 and 6).
In the genus _Planema_ the spots are as a rule fewer and clustered near the
body, while on both fore and hind wings there is a tendency to develop
clear wide band-like areas of orange or white (cf. Pl. VII).
Like the Acraeas the Planemas are principally mimicked by species of
_Pseudacraea_ and of _Papilio_. Some of the cases of resemblance between
_Planema_ and _Pseudacraea_ are among the most striking known. _Planema
macarista_ is one of those comparatively rare instances in which a model
shews a marked difference in the pattern of the two sexes. The clear area
on the fore wing of the male is deep orange, whereas in the female it is
somewhat different in shape, and, like the area on the hind wing, is white
(cf. Pl. VII, figs. 1 and 2). {35} _Pseudacraea eurytus hobleyi_ (Pl. VII,
figs. 6 and 7) shews a similar difference in the sexes, the male and female
of this species mimicking respectively the male and female of _Planema
macarista_. The case is made even more remarkable by the fact that both of
the sexual forms of _Planema macarista_ are mimicked by the Satyrine
_Elymnias phegea_ (Pl. VII, fig. 9), though in this species either the
black and white, or the black, white, and orange form may occur in either
sex. Among the best Papilionine mimics of the Planemas is _Papilio cynorta_
whose female is extraordinarily like the common _Planema epaea_ (Pl. VII,
figs. 5 and 10). The resemblance of the _planemoides_ female of _P.
dardanus_ to _P. poggei_ has already been noticed.
A striking feature of the African continent is the frequency with which
mimetic forms are found among the Lycaenidae. As a rule the "blues" rarely
exhibit mimetic analogies, but in Africa there are several species,
especially those of the genus _Mimacraea_, which closely resemble
Acraeines. Others again bear a marked resemblance to certain small
Pierines, _Citronophila similis_ from S. Nigeria for example being
extraordinarily like the common _Terias brigitta_, a small bright yellow
Pierine with black-edged wings.
A remarkable feature of the African continent is the absence of the
Pharmacophagus Swallow-tails. Of such Papilios as exhibit mimicry, and as
compared with the total number of the group present the proportion is
large, the majority resemble one or other {36} of the characteristic
Danaines, while a few such as _P. ridleyanus_ and _P. cynorta_ resemble
either an Acraeoid or a Planemoid model.
As in the Oriental region the African Pierines do not offer many instances
of mimetic analogies. The genus _Mylothris_, in which certain species are
characterised by orange patches at the bases of the undersurfaces of the
fore wings, is regarded by some authors as providing models for allied
genera such as _Belenois_ and _Phrissura_. But as neither models nor mimics
offer a marked divergence in appearance from the ordinary Pierine facies it
is doubtful whether much stress can be laid on these cases.
Africa also offers a few striking instances of mimicry in which day-flying
moths play a part. The conspicuous Geometer _Aletis helcita_ is an abundant
form, and with its strong red colour and black wing margins broken by white
it is a striking object in the preserved state. Among the forms which bear
a close resemblance to it are the Nymphaline _Euphaedra ruspina_, and the
Lycaenid _Telipna sanguinea_[18].
* * * * * {37}