existence by imitating the great protected group of Heliconidae;--a genus
of quite another family of most lovely small American butterflies, the
Erycinidae, and three genera of diurnal moths, also present species which
often mimic the same dominant 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 Heliconidae 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
Heliconidae. They both fly very slowly, they are both conspicuously
coloured, and they both abound in individuals; so that there is every
reason to believe that they possess a protection of a similar kind to
the Heliconidae, 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 Heliconidae themselves mimic other groups. Species of
Heliconia mimic Mechanitis, and every species of Napeogenes mimics some
other Heliconideous butterfly. This would seem to indicate that the
distasteful secretion is not produced alike by all members of the
family, and that where it is deficient protective imitation comes into
play. It is this, perhaps, that has caused such a general resemblance
among the Heliconidae, such a uniformity of type with great diversity of
colouring, since any aberration causing an insect to cease to look like
one of the family would inevitably lead to its being attacked, wounded,
and exterminated, even although it was not eatable.
In other parts of the world an exactly parallel series of facts have
been observed. The Danaidae and the Acraeidae of the Old World tropics form
in fact one great group with the Heliconidae. 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
allied 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 Natal 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. Acraea gea is copied in its very peculiar style
of colouration by the female of Papilio cynorta, by Panopaea hirce, and
by the female of Elymnias phegea. Acraea 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 Linnaean 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 Acraea
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 leuconoee with its semi-transparent white
wings, veined and spotted with black, is copied by the rare Papilio
idaeoides from the same islands.
In the Malay archipelago the very common and beautiful Euploea midamus
is so exactly mimicked by two rare Papilios (P. paradoxa and P. aenigma)
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
glossy 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 crimson, 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 essentially 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. aenomaus, 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 coeon, which is
unmistakeably imitated by the female tailed form of Papilio memnon.
These are both from Sumatra; but in North India P. coeon 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
temperate 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 entirely 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
Weir also found that this moth was refused by the Bullfinch, Chaffinch,
Yellow Hammer, and Red Bunting, but eaten after much hesitation by the
Robin. 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 sufficiently 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 mimicking butterflies of
various families do to the Heliconidae and Danaidae. It would be very
interesting to experiment on all white moths, to ascertain 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.
_Lepidoptera mimicking other Insects._
In the preceding cases we have found Lepidoptera imitating other species
of the same order, and such species only as we have good reason to
believe were free from the attacks of many insectivorous creatures; but
there are other instances in which they altogether lose the external
appearance of the order to which they belong, and take on the dress of
bees or wasps--insects which have an undeniable protection in their
stings. The Sesiidae and AEgeriidae, two families of day-flying moths, are
particularly remarkable in this respect, and a mere inspection of the
names given to the various species shows how the resemblance has struck
everyone. We have apiformis, vespiforme, ichneumoniforme, scoliaeforme,
sphegiforme (bee-like, wasp-like, ichneumon-like, &c.) and many others,
all indicating a resemblance to stinging Hymenoptera. In Britain we may
particularly notice Sesia bombiliformis, which very closely resembles
the male of the large and common humble bee, Bombus hortorum; Sphecia
craboniforme, which is coloured like a hornet, and is (on the authority
of Mr. Jenner Weir) much more like it when alive than when in the
cabinet, from the way in which it carries its wings; and the currant
clear-wing, Trochilium tipuliforme, which resembles a small black wasp
(Odynerus sinuatus) very abundant in gardens at the same season. It has
been so much the practice to look upon these resemblances as mere
curious analogies playing no part in the economy of nature, that we have
scarcely any observations of the habits and appearance when alive of the
hundreds of species of these groups in various parts of the world, or
how far they are accompanied by Hymenoptera, which they specifically
resemble. There are many species in India (like those figured by
Professor Westwood in his "Oriental Entomology") which have the hind
legs very broad and densely hairy, so as exactly to imitate the
brush-legged bees (Scopulipedes) which abound in the same country. In
this case we have more than mere resemblance of colour, for that which
is an important functional structure in the one group is imitated in
another whose habits render it perfectly useless.
_Mimicry among Beetles._
It may fairly be expected that if these imitations of one creature by
another really serve as a protection to weak and decaying species,
instances of the same kind will be found among other groups than the
Lepidoptera; and such is the case, although they are seldom so prominent
and so easily recognised as those already pointed out as occurring in
that order. A few very interesting examples may, however, be pointed out
in most of the other orders of insects. The Coleoptera or beetles that
imitate other Coleoptera of distinct groups are very numerous in
tropical countries, and they generally follow the laws already laid down
as regulating these phenomena. The insects which others imitate always
have a special protection, which leads them to be avoided as dangerous
or uneatable by small insectivorous animals; some have a disgusting
taste (analogous to that of the Heliconidae); others have such a hard and
stony covering that they cannot be crushed or digested; while a third
set are very active, and armed with powerful jaws, as well as having
some disagreeable secretion. Some species of Eumorphidae and Hispidae,
small flat or hemispherical beetles which are exceedingly abundant, and
have a disagreeable secretion, are imitated by others of the very
distinct group of Longicornes (of which our common musk-beetle may be
taken as an example). The extraordinary little Cyclopeplus batesii,
belongs to the same sub-family of this group as the Onychocerus scorpio
and O. concentricus, which have already been adduced as imitating with
such wonderful accuracy the bark of the trees they habitually frequent;
but it differs totally in outward appearance from every one of its
allies, having taken upon itself the exact shape and colouring of a
globular Corynomalus, a little stinking beetle with clubbed antennae. It
is curious to see how these clubbed antennae are imitated by an insect
belonging to a group with long slender antennae. The sub-family
Anisocerinae, to which Cyclopeplus belongs, is characterised by all its
members possessing a little knob or dilatation about the middle of the
antennae. This knob is considerably enlarged in C. batesii, and the
terminal portion of the antennae beyond it is so small and slender as to
be scarcely visible, and thus an excellent substitute is obtained for
the short clubbed antennae of the Corynomalus. Erythroplatis corallifer
is another curious broad flat beetle, that no one would take for a
Longicorn, since it almost exactly resembles Cephalodonta spinipes, one
of the commonest of the South American Hispidae; and what is still more
remarkable, another Longicorn of a distinct group, Streptolabis
hispoides, was found by Mr. Bates, which resembles the same insect with
equal minuteness,--a case exactly parallel to that among butterflies,
where species of two or three distinct groups mimicked the same
Heliconia. Many of the soft-winged beetles (Malacoderms) are excessively
abundant in individuals, and it is probable that they have some similar
protection, more especially as other species often strikingly resemble
them. A Longicorn beetle, Paeciloderma terminale, found in Jamaica, is
coloured exactly in the same way as a Lycus (one of the Malacoderms)
from the same island. Eroschema poweri, a Longicorn from Australia,
might certainly be taken for one of the same group, and several species
from the Malay Islands are equally deceptive. In the Island of Celebes I
found one of this group, having the whole body and elytra of a rich deep
blue colour, with the head only orange; and in company with it an insect
of a totally different family (Eucnemidae) with identically the same
colouration, and of so nearly the same size and form as to completely
puzzle the collector on every fresh occasion of capturing them. I have
been recently informed by Mr. Jenner Weir, who keeps a variety of small
birds, that none of them will touch our common "soldiers and sailors"
(species of Malacoderms), thus confirming my belief that they were a
protected group, founded on the fact of their being at once very
abundant, of conspicuous colours, and the objects of mimicry.
There are a number of the larger tropical weevils which have the
elytra and the whole covering of the body so hard as to be a great
annoyance to the entomologist, because in attempting to transfix them
the points of his pins are constantly turned. I have found it necessary
in these cases to drill a hole very carefully with the point of a
sharp penknife before attempting to insert a pin. Many of the fine
long-antennaed Anthribidae (an allied group) have to be treated in the
same way. We can easily understand that after small birds have in vain
attempted to eat these insects, they should get to know them by sight,
and ever after leave them alone, and it will then be an advantage for
other insects which are comparatively soft and eatable, to be mistaken
for them. We need not be surprised, therefore, to find that there are
many Longicorns which strikingly resemble the "hard beetles" of their
own district. In South Brazil, Acanthotritus dorsalis is strikingly
like a Curculio of the hard genus Heiliplus, and Mr. Bates assures me
that he found Gymnocerus cratosomoides (a Longicorn) on the same tree
with a hard Cratosomus (a weevil), which it exactly mimics. Again, the
pretty Longicorn, Phacellocera batesii, mimics one of the hard
Anthribidae of the genus Ptychoderes, having long slender antennae. In the
Moluccas we find Cacia anthriboides, a small Longicorn which might be
easily mistaken for a very common species of Anthribidae found in the
same districts; and the very rare Capnolymma stygium closely imitates
the common Mecocerus gazella, which abounded where it was taken. Doliops
curculionoides and other allied Longicorns from the Philippine Islands
most curiously resemble, both in form and colouring, the brilliant
Pachyrhynchi,--Curculionidae, which are almost peculiar to that group of
islands. The remaining family of Coleoptera most frequently imitated is
the Cicindelidae. The rare and curious Longicorn, Collyrodes lacordairei,
has exactly the form and colouring of the genus Collyris, while an
undescribed species of Heteromera is exactly like a Therates, and was
taken running on the trunks of trees, as is the habit of that group.
There is one curious example of a Longicorn mimicking a Longicorn, like
the Papilios and Heliconidae which mimic their own allies. Agnia
fasciata, belonging to the sub-family Hypselominae, and Nemophas grayi,
belonging to the Lamiinae, were taken in Amboyna on the same fallen tree
at the same time, and were supposed to be the same species till they
were more carefully examined, and found to be structurally quite
different. The colouring of these insects is very remarkable, being rich
steel-blue black, crossed by broad hairy bands of orange buff, and out
of the many thousands of known species of Longicorns they are probably
the only two which are so coloured. The Nemophas grayi is the larger,
stronger, and better armed insect, and belongs to a more widely spread
and dominant group, very rich in species and individuals, and is
therefore most probably the subject of mimicry by the other species.
_Beetles mimicking other Insects._
We will now adduce a few cases in which beetles imitate other insects,
and insects of other orders imitate beetles.
Charis melipona, a South American Longicorn of the family Necydalidae,
has been so named from its resemblance to a small bee of the genus
Melipona. It is one of the most remarkable cases of mimicry, since the
beetle has the thorax and body densely hairy like the bee, and the legs
are tufted in a manner most unusual in the order Coleoptera. Another
Longicorn, Odontocera odyneroides, has the abdomen banded with yellow,
and constricted at the base, and is altogether so exactly like a small
common wasp of the genus Odynerus, that Mr. Bates informs us he was
afraid to take it out of his net with his fingers for fear of being
stung. Had Mr. Bates's taste for insects been less omnivorous than it
was, the beetle's disguise might have saved it from his pin, as it had
no doubt often done from the beak of hungry birds. A larger insect,
Sphecomorpha chalybea, is exactly like one of the large metallic blue
wasps, and like them has the abdomen connected with the thorax by a
pedicel, rendering the deception most complete and striking. Many
Eastern species of Longicorns of the genus Oberea, when on the wing
exactly resemble Tenthredinidae, and many of the small species of
Hesthesis run about on timber, and cannot be distinguished from ants.
There is one genus of South American Longicorns that appears to mimic
the shielded bugs of the genus Scutellera. The Gymnocerous capucinus is
one of these, and is very like Pachyotris fabricii, one of the
Scutelleridae. The beautiful Gymnocerous dulcissimus is also very like
the same group of insects, though there is no known species that exactly
corresponds to it; but this is not to be wondered at, as the tropical
Hemiptera have been comparatively so little cared for by collectors.
_Insects mimicking Species of other Orders._
The most remarkable case of an insect of another order mimicking a
beetle is that of the Condylodera tricondyloides, one of the cricket
family from the Philippine Islands, which is so exactly like a
Tricondyla (one of the tiger beetles), that such an experienced
entomologist as Professor Westwood placed it among them in his cabinet,
and retained it there a long time before he discovered his mistake! Both
insects run along the trunks of trees, and whereas Tricondylas are very
plentiful, the insect that mimics it is, as in all other cases, very
rare. Mr. Bates also informs us that he found at Santarem on the Amazon,
a species of locust which mimicked one of the tiger beetles of the genus
Odontocheila, and was found on the same trees which they frequented.
There are a considerable number of Diptera, or two-winged flies, that
closely resemble wasps and bees, and no doubt derive much benefit from
the wholesome dread which those insects excite. The Midas dives, and
other species of large Brazilian flies, have dark wings and metallic
blue elongate bodies, resembling the large stinging Sphegidae of the same
country; and a very large fly of the genus Asilus has black-banded
wings and the abdomen tipped with rich orange, so as exactly to resemble
the fine bee Euglossa dimidiata, and both are found in the same parts of
South America. We have also in our own country species of Bombylius
which are almost exactly like bees. In these cases the end gained by the
mimicry is no doubt freedom from attack, but it has sometimes an
altogether different purpose. There are a number of parasitic flies
whose larvae feed upon the larvae of bees, such as the British genus
Volucella and many of the tropical Bombylii, and most of these are
exactly like the particular species of bee they prey upon, so that they
can enter their nests unsuspected to deposit their eggs. There are also
bees that mimic bees. The cuckoo bees of the genus Nomada are parasitic
on the Andrenidae, and they resemble either wasps or species of Andrena;
and the parasitic humble-bees of the genus Apathus almost exactly
resemble the species of humble-bees in whose nests they are reared. Mr.
Bates informs us that he found numbers of these "cuckoo" bees and flies
on the Amazon, which all wore the livery of working bees peculiar to the
same country.
There is a genus of small spiders in the tropics which feed on ants, and
they are exactly like ants themselves, which no doubt gives them more
opportunity of seizing their prey; and Mr. Bates found on the Amazon a
species of Mantis which exactly resembled the white ants which it fed
upon, as well as several species of crickets (Scaphura), which resembled
in a wonderful manner different sand-wasps of large size, which are
constantly on the search for crickets with which to provision their
nests.
Perhaps the most wonderful case of all is the large caterpillar
mentioned by Mr. Bates, which startled him by its close resemblance to a
small snake. The first three segments behind the head were dilatable at
the will of the insect, and had on each side a large black pupillated
spot, which resembled the eye of the reptile. Moreover, it resembled a
poisonous viper, not a harmless species of snake, as was proved by the
imitation of keeled scales on the crown produced by the recumbent feet,
as the caterpillar threw itself backward!
The attitudes of many of the tropical spiders are most extraordinary and
deceptive, but little attention has been paid to them. They often mimic
other insects, and some, Mr. Bates assures us, are exactly like flower
buds, and take their station in the axils of leaves, where they remain
motionless waiting for their prey.
_Cases of Mimicry among the Vertebrata._
Having thus shown how varied and extraordinary are the modes in which
mimicry occurs among insects, we have now to enquire if anything of the
same kind is to be observed among vertebrated animals. When we consider
all the conditions necessary to produce a good deceptive imitation, we
shall see at once that such can very rarely occur in the higher animals,
since they possess none of those facilities for the almost infinite
modifications of external form which exist in the very nature of insect
organization. The outer covering of insects being more or less solid
and horny, they are capable of almost any amount of change of form and
appearance without any essential modification internally. In many groups
the wings give much of the character, and these organs may be much
modified both in form and colour without interfering with their special
functions. Again, the number of species of insects is so great, and
there is such diversity of form and proportion in every group, that the
chances of an accidental approximation in size, form, and colour, of one
insect to another of a different group, are very considerable; and it is
these chance approximations that furnish the basis of mimicry, to be
continually advanced and perfected by the survival of those varieties
only which tend in the right direction.