Among the reefs of rock upon the Australian coast, an explorer's dredge
often brings up to the surface some tangled tresses of reddish seaweed,
which, when placed for a while in a bucket of water, begin slowly to
uncoil themselves as if endowed with animal life, and finally to swim
about with a gentle tremulous motion in a mute inquiring way from side
to side of the pail that contains them. Looked at closely with an
attentive eye, the complex moving mass gradually resolves itself into
two parts: one a ruddy seaweed with long streaming fronds; the other, a
strangely misshapen and dishevelled pipe-fish, exactly imitating the
weed itself in form and colour. When removed from the water, this queer
pipe-fish proves in general outline somewhat to resemble the well-known
hippocampus or sea-horse of the aquariums, whose dried remains, in a
mummified state, form a standing wonder in many tiny domestic museums.
But the Australian species, instead of merely mimicking the knight on a
chess-board, looks rather like a hippocampus in the most advanced stage
of lunacy, with its tail and fins and the appendages of its spines
flattened out into long thin streaming filaments, utterly
indistinguishable in hue and shape from the fucus round which the
creature clings for support with its prehensile tail. Only a rude and
shapeless rough draught of a head, vaguely horse-like in contour, and
inconspicuously provided with an unobtrusive snout and a pair of very
unnoticeable eyes, at all suggests to the most microscopic observer its
animal nature. Taken as a whole, nobody could at first sight distinguish
it in any way from the waving weed among which it vegetates.
Clearly, this curious Australian cousin of the Mediterranean sea-horses
has acquired so marvellous a resemblance to a bit of fucus in order to
deceive the eyes of its ever-watchful enemies, and to become
indistinguishable from the uneatable weed whose colour and form it so
surprisingly imitates. Protective resemblances of the sort are extremely
common among the pipe-fish family, and the reason why they should be so
is no doubt sufficiently obvious at first sight to any reflecting
mind--such, for example, as the intelligent reader's. Pipe-fish, as
everybody knows, are far from giddy. They do not swim in the vortex of
piscine dissipation. Being mostly small and defenceless creatures,
lurking among the marine vegetation of the shoals and reefs, they are
usually accustomed to cling for support by their snake-like tails to the
stalks or leaves of those submerged forests. The omniscient schoolboy
must often have watched in aquariums the habits and manners of the
common sea-horses, twisted together by their long thin bodies into one
inextricable mass of living matwork, or anchored firmly with a treble
serpentine coil to some projecting branch of coralline or of quivering
sea-wrack. Bad swimmers by nature, utterly unarmed, and wholly
undefended by protective mail, the pipe-fish generally can neither fight
nor run away: and therefore they depend entirely for their lives upon
their peculiar skulking and lurking habits. Their one mode of defence is
not to show themselves; discretion is the better part of their valour;
they hide as much as possible among the thickest seaweed, and trust to
Providence to escape observation.
Now, with any animals thus constituted, cowards by hereditary
predilection, it must necessarily happen that the more brightly coloured
or obtrusive individuals will most readily be spotted and most
unceremoniously devoured by their sharp-sighted foes, the predatory
fishes. On the other hand, just in proportion as any particular
pipe-fish happens to display any chance resemblance in colour or
appearance to the special seaweed in whose folds it lurks, to that
extent will it be likely to escape detection, and to hand on its
peculiarities to its future descendants. A long-continued course of the
simple process thus roughly described must of necessity result at last
in the elimination of all the most conspicuous pipe-fish, and the
survival of all those unobtrusive and retiring individuals which in any
respect happen to resemble the fucus or coralline among which they
dwell. Hence, in many places, various kinds of pipe-fish exhibit an
extraordinary amount of imitative likeness to the sargasso or seaweed to
whose tags they cling; and in the three most highly developed Australian
species the likeness becomes so ridiculously close that it is with
difficulty one can persuade oneself one is really and truly looking at a
fish, and not at a piece of strangely animated and locomotive fucus.
Of course, the playful pipe-fish is by no means alone in his assumption
of so neat and effective a disguise. Protective resemblances of just the
same sort as that thus exhibited by this extraordinary little creature
are common throughout the whole range of nature; instances are to be
found in abundance, not only among beasts, birds, reptiles, and fishes,
but even among caterpillars, butterflies, and spiders, of species which
preserve the strictest incognito. Everywhere in the world, animals and
plants are perpetually masquerading in various assumed characters; and
sometimes their make-up is so exceedingly good as to take in for a while
not merely the uninstructed ordinary observer, but even the scientific
and systematic naturalist.
A few selected instances of such successful masquerading will perhaps
best serve to introduce the general principles upon which all animal
mimicry ultimately depends. Indeed, naturalists of late years have been
largely employed in fishing up examples from the ends of the earth and
from the depths of the sea for the elucidation of this very subject.
There is a certain butterfly in the islands of the Malay Archipelago
(its learned name, if anybody wishes to be formally introduced, is
_Kallima paralekta_) which always rests among dead or dry leaves, and
has itself leaf-like wings, all spotted over at intervals with wee
speckles to imitate the tiny spots of fungi on the foliage it resembles.
The well-known stick and leaf insects from the same rich neighbourhood
in like manner exactly mimic the twigs and leaves of the forest among
which they lurk: some of them look for all the world like little bits of
walking bamboo, while others appear in all varieties of hue, as if
opening buds and full-blown leaves and pieces of yellow foliage
sprinkled with the tints and moulds of decay had of a sudden raised
themselves erect upon six legs, and begun incontinently to perambulate
the Malayan woodlands like vegetable Frankensteins in all their glory.
The larva of one such deceptive insect, observed in Nicaragua by
sharp-eyed Mr. Belt, appeared at first sight like a mere fragment of the
moss on which it rested, its body being all prolonged into little
thread-like green filaments, precisely imitating the foliage around it.
Once more, there are common flies which secure protection for themselves
by growing into the counterfeit presentment of wasps or hornets, and so
obtaining immunity from the attacks of birds or animals. Many of these
curiously mimetic insects are banded with yellow and black in the very
image of their stinging originals, and have their tails sharpened, _in
terrorem_, into a pretended sting, to give point and verisimilitude to
the deceptive resemblance. More curious still, certain South American
butterflies of a perfectly inoffensive and edible family mimic in every
spot and line of colour sundry other butterflies of an utterly unrelated
and fundamentally dissimilar type, but of so disagreeable a taste as
never to be eaten by birds or lizards. The origin of these curious
resemblances I shall endeavour to explain (after Messrs. Bates and
Wallace) a little farther on: for the present it is enough to observe
that the extraordinary resemblances thus produced have often deceived
the very elect, and have caused experienced naturalists for a time to
stick some deceptive specimen of a fly among the wasps and hornets, or
some masquerading cricket into the midst of a cabinet full of saw-flies
or ichneumons.
Let us look briefly at the other instances of protective coloration in
nature generally which lead up to these final bizarre exemplifications
of the masquerading tendency.
Wherever all the world around is remarkably uniform in colour and
appearance, all the animals, birds, and insects alike necessarily
disguise themselves in its prevailing tint to escape observation. It
does not matter in the least whether they are predatory or defenceless,
the hunters or the hunted: if they are to escape destruction or
starvation, as the case may be, they must assume the hue of all the rest
of nature about them. In the arctic snows, for example, all animals,
without exception, must needs be snow-white. The polar bear, if he were
brown or black, would immediately be observed among the unvaried
ice-fields by his expected prey, and could never get a chance of
approaching his quarry unperceived at close quarters. On the other hand,
the arctic hare must equally be dressed in a snow-white coat, or the
arctic fox would too readily discover him and pounce down upon him
off-hand; while, conversely, the fox himself, if red or brown, could
never creep upon the unwary hare without previous detection, which would
defeat his purpose. For this reason, the ptarmigan and the willow grouse
become as white in winter as the vast snow-fields under which they
burrow; the ermine changes his dusky summer coat for the expensive
wintry suit beloved of British Themis; the snow-bunting acquires his
milk-white plumage; and even the weasel assimilates himself more or less
in hue to the unvarying garb of arctic nature. To be out of the fashion
is there quite literally to be out of the world: no half-measures will
suit the stern decree of polar biology; strict compliance with the law
of winter change is absolutely necessary to success in the struggle for
existence.
Now, how has this curious uniformity of dress in arctic animals been
brought about? Why, simply by that unyielding principle of Nature which
condemns the less adapted for ever to extinction, and exalts the better
adapted to the high places of her hierarchy in their stead. The
ptarmigan and the snow-buntings that look most like the snow have for
ages been least likely to attract the unfavourable attention of arctic
fox or prowling ermine; the fox or ermine that came most silently and
most unperceived across the shifting drifts has been most likely to
steal unawares upon the heedless flocks of ptarmigan and snow-bunting.
In the one case protective colouring preserves the animal from himself
being devoured; in the other case it enables him the more easily to
devour others. And since 'Eat or be eaten' is the shrill sentence of
Nature upon all animal life, the final result is the unbroken whiteness
of the arctic fauna in all its developments of fur or feather.
Where the colouring of nature is absolutely uniform, as among the arctic
snows or the chilly mountain tops, the colouring of the animals is
uniform too. Where it is slightly diversified from point to point, as in
the sands of the desert, the animals that imitate it are speckled or
diversified with various soft neutral tints. All the birds, reptiles,
and insects of Sahara, says Canon Tristram, copy closely the grey or
isabelline colour of the boundless sands that stretch around them. Lord
George Campbell, in his amusing 'Log Letters from the "Challenger,"'
mentions a butterfly on the shore at Amboyna which looked exactly like a
bit of the beach, until it spread its wings and fluttered away gaily to
leeward. Soles and other flat-fish similarly resemble the sands or banks
on which they lie, and accommodate themselves specifically to the
particular colour of their special bottom. Thus the flounder imitates
the muddy bars at the mouths of rivers, where he loves to half bury
himself in the congenial ooze; the sole, who rather affects clean hard
sand-banks, is simply sandy and speckled with grey; the plaice, who goes
in by preference for a bed of mixed pebbles, has red and yellow spots
scattered up and down irregularly among the brown, to look as much as
possible like agates and carnelians: the brill, who hugs a still rougher
ledge, has gone so far as to acquire raised lumps or tubercles on his
upper surface, which make him seem like a mere bit of the shingle-strewn
rock on which he reposes. In short, where the environment is most
uniform the colouring follows suit: just in proportion as the
environment varies from place to place, the colouring must vary in order
to simulate it. There is a deep biological joy in the term
'environment'; it almost rivals the well-known consolatory properties of
that sweet word 'Mesopotamia.' 'Surroundings,' perhaps, would equally
well express the meaning, but then, as Mr. Wordsworth justly observes,
'the difference to me!'
Between England and the West Indies, about the time when one begins to
recover from the first bout of sea-sickness, we come upon a certain
sluggish tract of ocean, uninvaded by either Gulf Stream or arctic
current, but slowly stagnating in a sort of endless eddy of its own, and
known to sailors and books of physical geography as the Sargasso Sea.
The sargasso or floating seaweed from which it takes its poetical name
is a pretty yellow rootless alga, swimming in vast quantities on the
surface of the water, and covered with tiny bladder-like bodies which at
first sight might easily be mistaken for amber berries. If you drop a
bucket over the ship's side and pull up a tangled mass of this beautiful
seaweed, it will seem at first to be all plant alike; but, when you come
to examine its tangles closely, you will find that it simply swarms with
tiny crabs, fishes, and shrimps, all coloured so precisely to shade that
they look exactly like the sargasso itself. Here the colour about is
less uniform than in the arctic snows, but, so far as the
sargasso-haunting animals are concerned, it comes pretty much to the
same thing. The floating mass of weed is their whole world, and they
have had to accommodate themselves to its tawny hue under pain of death,
immediate and violent.
Caterpillars and butterflies often show us a further step in advance in
the direction of minute imitation of ordinary surroundings. Dr. Weismann
has published a very long and learned memoir, fraught with the best
German erudition and prolixity, upon this highly interesting and obscure
subject. As English readers, however, not unnaturally object to trudging
through a stout volume on the larva of the sphinx moth, conceived in the
spirit of those patriarchal ages of Hilpa and Shalum, when man lived to
nine hundred and ninety-nine years, and devoted a stray century or so
without stint to the work of education, I shall not refer them to Dr.
Weismann's original treatise, as well translated and still further
enlarged by Mr. Raphael Meldola, but will present them instead with a
brief _résumé_, boiled down and condensed into a patent royal elixir of
learning. Your caterpillar, then, runs many serious risks in early life
from the annoying persistence of sundry evil-disposed birds, who insist
at inconvenient times in picking him off the leaves of gooseberry bushes
and other his chosen places of residence. His infant mortality, indeed,
is something simply appalling, and it is only by laying the eggs that
produce him in enormous quantities that his fond mother the butterfly
ever succeeds in rearing on an average two of her brood to replace the
imago generation just departed. Accordingly, the caterpillar has been
forced by adverse circumstances to assume the most ridiculous and
impossible disguises, appearing now in the shape of a leaf or stem, now
as a bundle of dark-green pine needles, and now again as a bud or
flower, all for the innocent purpose of concealing his whereabouts from
the inquisitive gaze of the birds his enemies.
When the caterpillar lives on a plant like a grass, the ribs or veins of
which run up and down longitudinally, he is usually striped or streaked
with darker lines in the same direction as those on his native foliage.
When, on the contrary, he lives upon broader leaves, provided with a
midrib and branching veins, his stripes and streaks (not to be out of
the fashion) run transversely and obliquely, at exactly the same angle
as those of his wonted food-plant. Very often, if you take a green
caterpillar of this sort away from his natural surroundings, you will be
surprised at the conspicuousness of his pale lilac or mauve markings;
surely, you will think to yourself, such very distinct variegation as
that must betray him instantly to his watchful enemies. But no; if you
replace him gently where you first found him, you will see that the
lines exactly harmonise with the joints and shading of his native leaf:
they are delicate representations of the soft shadow cast by a rib or
vein, and the local colour is precisely what a painter would have had to
use in order to produce the corresponding effect. The shadow of
yellowish green is, of course, always purplish or lilac. It may at first
sight seem surprising that a caterpillar should possess so much artistic
sense and dexterity; but then the penalty for bungling or inharmonious
work is so very severe as necessarily to stimulate his imitative genius.
Birds are for ever hunting him down among the green leaves, and only
those caterpillars which effectually deceive them by their admirable
imitations can ever hope to survive and become the butterflies who hand
on their larval peculiarities to after ages. Need I add that the
variations are, of course, unconscious, and that accident in the first
place is ultimately answerable for each fresh step in the direction of
still closer simulation?
The geometric moths have brown caterpillars, which generally stand erect
when at rest on the branches of trees and so resemble small twigs; and,
in order that the resemblance may be the more striking, they are often
covered with tiny warts which look like buds or knots upon the surface.
The larva of that familiar and much-dreaded insect, the death's-head
hawk-moth, feeds as a rule on the foliage of the potato, and its very
varied colouring, as Sir John Lubbock has pointed out, so beautifully
harmonises with the brown of the earth, the yellow and green of the
leaves, and the faint purplish blue of the lurid flowers, that it can
only be distinguished when the eye happens accidentally to focus itself
exactly upon the spot occupied by the unobtrusive caterpillar. Other
larvæ which frequent pine trees have their bodies covered with tufts of
green hairs that serve to imitate the peculiar pine foliage. One queer
little caterpillar, which lives upon the hoary foliage of the
sea-buckthorn, has a grey-green body, just like the buckthorn leaves,
relieved by a very conspicuous red spot which really represents in size
and colour one of the berries that grow around it. Finally the larva of
the elephant hawk-moth, which grows to a very large size, has a pair of
huge spots that seem like great eyes; and direct experiment establishes
the fact that small birds mistake it for a young snake, and stand in
terrible awe of it accordingly, though it is in reality a perfectly
harmless insect, and also, as I am credibly informed (for I cannot speak
upon the point from personal experience), a very tasty and
well-flavoured insect, and 'quite good to eat' too, says an eminent
authority. One of these big snake-like caterpillars once frightened Mr.
Bates himself on the banks of the Amazon.
Now, I know that cantankerous person, the universal objector, has all
along been bursting to interrupt me and declare that he himself
frequently finds no end of caterpillars, and has not the slightest
difficulty at all in distinguishing them with the naked eye from the
leaves and plants among which they are lurking. But observe how promptly
we crush and demolish this very inconvenient and disconcerting critic.
The caterpillars _he_ finds are almost all hairy ones, very conspicuous
and easy to discover--'woolly bears,' and such like common and unclean
creatures--and the reason they take no pains to conceal themselves from
his unobservant eyes is simply this: nobody on earth wants to discover
them. For either they are protectively encased in horrid hairs, which
get down your throat and choke you and bother you (I speak as a bird,
from the point of view of a confirmed caterpillar eater), or else they
are bitter and nasty to the taste, like the larva of the spurge moth and
the machaon butterfly. These are the ordinary brown and red and banded
caterpillars that the critical objector finds in hundreds on his
peregrinations about his own garden--commonplace things which the
experienced naturalist has long since got utterly tired of. But has
your rash objector ever lighted upon that rare larva which lives among
the periwinkles, and exactly imitates a periwinkle petal? Has he ever
discovered those deceptive creatures which pretend for all the world to
be leaves of lady's-bedstraw, or dress themselves up as flowers of
buttonweed? Has he ever hit upon those immoral caterpillars which
wriggle through life upon the false pretence that they are only the
shadows of projecting ribs on the under surface of a full-grown lime
leaf? No, not he; he passes them all by without one single glance of
recognition; and when the painstaking naturalist who has hunted them
every one down with lens and butterfly net ventures tentatively to
describe their personal appearance, he comes up smiling with his great
russet woolly bear comfortably nestling upon a green cabbage leaf, and
asks you in a voice of triumphant demonstration, where is the trace of
concealment or disguise in that amiable but very inedible insect? Go to,
Sir Critic, I will have none of you; I only use you for a metaphorical
marionette to set up and knock down again, as Mr. Punch in the street
show knocks down the policeman who comes to arrest him, and the grimy
black personage of sulphurous antecedents who pops up with a fizz
through the floor of his apartment.
Queerer still than the caterpillars which pretend to be leaves or
flowers for the sake of protection are those truly diabolical and
perfidious Brazilian spiders which, as Mr. Bates observed, are
brilliantly coloured with crimson and purple, but 'double themselves up
at the base of leaf-stalks, so as to resemble flower buds, and thus
deceive the insects upon which they prey.' There is something hideously
wicked and cruel in this lowest depth of imitative infamy. A flower-bud
is something so innocent and childlike; and to disguise oneself as such
for purposes of murder and rapine argues the final abyss of arachnoid
perfidy. It reminds one of that charming and amiable young lady in Mr.
Robert Louis Stevenson's 'Dynamiter,' who amused herself in moments of
temporary gaiety by blowing up inhabited houses, inmates and all, out of
pure lightness of heart and girlish frivolity. An Indian mantis or
praying insect, a little less wicked, though no less cruel than the
spiders, deceives the flies who come to his arms under the false
pretence of being a quiet leaf, upon which they may light in safety for
rest and refreshment. Yet another abandoned member of the same family,
relying boldly upon the resources of tropical nature, gets itself up as
a complete orchid, the head and fangs being moulded in the exact image
of the beautiful blossom, and the arms folding treacherously around the
unhappy insect which ventures to seek for honey in its deceptive jaws.
Happily, however, the tyrants and murderers do not always have things
all their own way. Sometimes the inoffensive prey turn the tables upon
their torturers with distinguished success. For example, Mr. Wallace
noticed a kind of sand-wasp, in Borneo, much given to devouring
crickets; but there was one species of cricket which exactly reproduced
the features of the sand-wasps, and mixed among them on equal terms
without fear of detection. Mr. Belt saw a green leaf-like locust in
Nicaragua, overrun by foraging ants in search of meat for dinner, but
remaining perfectly motionless all the time, and evidently mistaken by
the hungry foragers for a real piece of the foliage it mimicked. So
thoroughly did this innocent locust understand the necessity for
remaining still, and pretending to be a leaf under all advances, that
even when Mr. Belt took it up in his hands it never budged an inch, but
strenuously preserved its rigid leaf-like attitude. As other insects
'sham dead,' this ingenious creature shammed vegetable.
In order to understand how cases like these begin to arise, we must
remember that first of all they start of necessity from very slight and
indefinite resemblances, which succeed as it were by accident in
occasionally eluding the vigilance of enemies. Thus, there are stick
insects which only look like long round cylinders, not obviously
stick-shaped, but rudely resembling a bit of wood in outline only. These
imperfectly mimetic insects may often obtain a casual immunity from
attack by being mistaken for a twig by birds or lizards. There are
others, again, in which natural selection has gone a step further, so as
to produce upon their bodies bark-like colouring and rough patches which
imitate knots, wrinkles, and leaf-buds. In these cases the protection
given is far more marked, and the chances of detection are
proportionately lessened. But sharp-eyed birds, with senses quickened by
hunger, the true mother of invention, must learn at last to pierce such
flimsy disguises, and suspect a stick insect in the most
innocent-looking and apparently rigid twigs. The final step, therefore,
consists in the production of that extraordinary actor, the _Xeroxylus
laceratus_, whose formidable name means no more than 'ragged dry-stick,'
and which really mimics down to the minutest particular a broken twig,
overgrown with mosses, liverworts, and lichens.
Take, on the other hand, the well-known case of that predaceous mantis
which exactly imitates the white ants, and, mixing with them like one of
their own horde, quietly devours a stray fat termite or so, from time to
time, as occasion offers. Here we must suppose that the ancestral mantis
happened to be somewhat paler and smaller than most of its
fellow-tribesmen, and so at times managed unobserved to mingle with the
white ants, especially in the shade or under a dusky sky, much to the
advantage of its own appetite. But the termites would soon begin to
observe the visits of their suspicious friend, and to note their
coincidence with the frequent mysterious disappearance of a
fellow-townswoman, evaporated into space, like the missing young women
in neat cloth jackets who periodically vanish from the London suburbs.
In proportion as their reasonable suspicions increased, the termites
would carefully avoid all doubtful looking mantises; but, at the same
time, they would only succeed in making the mantises which survived
their inquisition grow more and more closely to resemble the termite
pattern in all particulars. For any mantis which happened to come a
little nearer the white ants in hue or shape would thereby be enabled to
make a more secure meal upon his unfortunate victims; and so the very
vigilance which the ants exerted against his vile deception would itself
react in time against their own kind, by leaving only the most ruthless
and indistinguishable of their foes to become the parents of future
generations of mantises.
Once more, the beetles and flies of Central America must have learned by
experience to get out of the way of the nimble Central American lizards
with great agility, cunning, and alertness. But green lizards are less
easy to notice beforehand than brown or red ones; and so the lizards of
tropical countries are almost always bright green, with complementary
shades of yellow, grey, and purple, just to fit them in with the foliage
they lurk among. Everybody who has ever hunted the green tree-toads on
the leaves of waterside plants on the Riviera must know how difficult it
is to discriminate these brilliant leaf-coloured creatures from the
almost identical background on which they rest. Now, just in proportion
as the beetles and flies grow still more cautious, even the green
lizards themselves fail to pick up a satisfactory livelihood; and so at
last we get that most remarkable Nicaraguan form, decked all round with
leaf-like expansions, and looking so like the foliage on which it rests
that no beetle on earth can possibly detect it. The more cunning you get
your detectives, the more cunning do the thieves become to outwit them.
Look, again, at the curious life-history of the flies which dwell as
unbidden guests or social parasites in the nests and hives of wild
honey-bees. These burglarious flies are belted and bearded in the very
self-same pattern as the bumble-bees themselves; but their larvæ live
upon the young grubs of the hive, and repay the unconscious hospitality
of the busy workers by devouring the future hope of their unwilling
hosts. Obviously, any fly which entered a bee-hive could only escape
detection and extermination at the hands (or stings) of its outraged
inhabitants, provided it so far resembled the real householders as to be
mistaken at a first glance by the invaded community for one of its own
numerous members. Thus any fly which showed the slightest superficial
resemblance to a bee might at first be enabled to rob honey for a time
with comparative impunity, and to lay its eggs among the cells of the
helpless larvæ. But when once the vile attempt was fairly discovered,
the burglars could only escape fatal detection from generation to
generation just in proportion as they more and more closely approximated
to the shape and colour of the bees themselves. For, as Mr. Belt has
well pointed out, while the mimicking species would become naturally
more numerous from age to age, the senses of the mimicked species would
grow sharper and sharper by constant practice in detecting and punishing
the unwelcome intruders.
It is only in external matters, however, that the appearance of such
mimetic species can ever be altered. Their underlying points of
structure and formative detail always show to the very end (if only one
happens to observe them) their proper place in a scientific
classification. For instance, these same parasitic flies which so
closely resemble bees in their shape and colour have only one pair of
wings apiece, like all the rest of the fly order, while the bees of
course have the full complement of two pairs, an upper and an under,
possessed by them in common with all other well-conducted members of the
hymenopterous family. So, too, there is a certain curious American
insect, belonging to the very unsavoury tribe which supplies London
lodging-houses with one of their most familiar entomological specimens;
and this cleverly disguised little creature is banded and striped in
every part exactly like a local hornet, for whom it evidently wishes
itself to be mistaken. If you were travelling in the wilder parts of
Colorado you would find a close resemblance to Buffalo Bill was no mean
personal protection. Hornets, in fact, are insects to which birds and
other insectivorous animals prefer to give a very wide berth, and the
reason why they should be imitated by a defenceless beetle must be
obvious to the intelligent student. But while the vibrating wing-cases
of this deceptive masquerader are made to look as thin and hornet-like
as possible, in all underlying points of structure any competent
naturalist would see at once that the creature must really be classed
among the noisome Hemiptera. I seldom trouble the public with a Greek or
Latin name, but on this occasion I trust I may be pardoned for not
indulging in all the ingenuous bluntness of the vernacular.
Sometimes this effective mimicry of stinging insects seems to be even
consciously performed by the tiny actors. Many creatures, which do not
themselves possess stings, nevertheless endeavour to frighten their
enemies by assuming the characteristic hostile attitudes of wasps or
hornets. Everybody in England must be well acquainted with those common
British earwig-looking insects, popularly known as the devil's
coach-horses, which, when irritated or interfered with, cock up their
tails behind them in the most aggressive fashion, exactly reproducing
the threatening action of an angry scorpion. Now, as a matter of fact,
the devil's coach-horse is quite harmless, but I have often seen, not
only little boys and girls, but also chickens, small birds, and
shrew-mice, evidently alarmed at his minatory attitude. So, too, the
bumble-bee flies, which are inoffensive insects got up in sedulous
imitation of various species of wild bee, flit about and buzz angrily in
the sunlight, quite after the fashion of the insects they mimic; and
when disturbed they pretend to get excited, and seem as if they wished
to fly in their assailant's face and roundly sting him. This curious
instinct may be put side by side with the parallel instinct of shamming
dead, possessed by many beetles and other small defenceless species.
Certain beetles have also been modified so as exactly to imitate wasps;
and in these cases the beetle waist, usually so solid, thick, and
clumsy, grows as slender and graceful as if the insects had been
supplied with corsets by a fashionable West End house. But the greatest
refinement of all is perhaps that noticed in certain allied species
which mimic bees, and which have acquired useless little tufts of hair
on their hind shanks to represent the dilated and tufted
pollen-gathering apparatus of the true bees.
I have left to the last the most marvellous cases of mimicry of
all--those noticed among South American butterflies by Mr. Bates, who
found that certain edible kinds exactly resembled a handsome and
conspicuous but bitter-tasted species 'in every shade and stripe of
colour.' Several of these South American imitative insects long deceived
the very entomologists; and it was only by a close inspection of their
structural differences that the utter distinctness of the mimickers and
the mimicked was satisfactorily settled. Scarcely less curious is the
case of Mr. Wallace's Malayan orioles, two species of which exactly copy
two pugnacious honey-suckers in every detail of plumage and coloration.
As the honey-suckers are avoided by birds of prey, owing to their
surprising strength and pugnacity, the orioles gain immunity from attack
by their close resemblance to the protected species. When Dr. Sclater,
the distinguished ornithologist, was examining Mr. Forbes's collections
from Timorlaut, even his experienced eye was so taken in by another of
these deceptive bird-mimicries that he classified two birds of totally
distinct families as two different individuals of the same species.
Even among plants a few instances of true mimicry have been observed. In
the stony African Karoo, where every plant is eagerly sought out for
food by the scanty local fauna, there are tubers which exactly resemble
the pebbles around them; and I have little doubt that our perfectly
harmless English dead-nettle secures itself from the attacks of browsing
animals by its close likeness to the wholly unrelated, but
well-protected, stinging-nettle.
Finally, we must not forget the device of those animals which not merely
assimilate themselves in colour to the ordinary environment in a general
way, but have also the power of adapting themselves at will to whatever
object they may happen to lie against. Cases like that of the ptarmigan,
which in summer harmonises with the brown heather and grey rock, while
in winter it changes to the white of the snow-fields, lead us up
gradually to such ultimate results of the masquerading tendency. There
is a tiny crustacean, the chameleon shrimp, which can alter its hue to
that of any material on which it happens to rest. On a sandy bottom it
appears grey or sand-coloured; when lurking among seaweed it becomes
green, or red, or brown, according to the nature of its momentary
background. Probably the effect is quite unconscious, or at least
involuntary, like blushing with ourselves--and nobody ever blushes on
purpose, though they do say a distinguished poet once complained that an
eminent actor did not follow his stage directions because he omitted to
obey the rubrical remark, 'Here Harold purples with anger.' The change
is produced by certain automatic muscles which force up particular
pigment cells above the others, green coming to the top on a green
surface, red on a ruddy one, and brown or grey where the circumstances
demand them. Many kinds of fish similarly alter their colour to suit
their background by forcing forward or backward certain special
pigment-cells known as chromatophores, whose various combinations
produce at will almost any required tone or shade. Almost all reptiles
and amphibians possess the power of changing their hue in accordance
with their environment in a very high degree; and among certain
tree-toads and frogs it is difficult to say what is the normal
colouring, as they vary indefinitely from buff and dove-colour to
chocolate-brown, rose, and even lilac.
But of all the particoloured reptiles the chameleon is by far the best
known, and on the whole the most remarkable for his inconstancy of
coloration. Like a lacertine Vicar of Bray, he varies incontinently from
buff to blue, and from blue back to orange again, under stress of
circumstances. The mechanism of this curious change is extremely
complex. Tiny corpuscles of different pigments are sometimes hidden in
the depths of the chameleon's skin, and sometimes spread out on its
surface in an interlacing network of brown or purple. In addition to
this prime colouring matter, however, the animal also possesses a normal
yellow pigment, and a bluish layer in the skin which acts like the
iridium glass so largely employed by Dr. Salviati, being seen as
straw-coloured with a transmitted light, but assuming a faint lilac tint
against an opaque absorbent surface. While sleeping the chameleon
becomes almost white in the shade, but if light falls upon him he slowly
darkens by an automatic process. The movements of the corpuscles are
governed by opposite nerves and muscles, which either cause them to bury
themselves under the true skin, or to form an opaque ground behind the
blue layer, or to spread out in a ramifying mass on the outer surface,
and so produce as desired almost any necessary shade of grey, green,
black, or yellow. It is an interesting fact that many chrysalids undergo
precisely similar changes of colour in adaptation to the background
against which they suspend themselves, being grey on a grey surface,
green on a green one, and even half black and half red when hung up
against pieces of particoloured paper.
Nothing could more beautifully prove the noble superiority of the human
intellect than the fact that while our grouse are russet-brown to suit
the bracken and heather, and our caterpillars green to suit the lettuce
and the cabbage leaves, our British soldier should be wisely coated in
brilliant scarlet to form an effective mark for the rifles of an enemy.
Red is the easiest of all colours at which to aim from a great distance;
and its selection by authority for the uniform of unfortunate Tommy
Atkins reminds me of nothing so much as Mr. McClelland's exquisite
suggestion that the peculiar brilliancy of the Indian river carps makes
them serve 'as a better mark for kingfishers, terns, and other birds
which are destined to keep the number of these fishes in check.' The
idea of Providence and the Horse Guards conspiring to render any
creature an easier target for the attacks of enemies is worthy of the
decadent school of natural history, and cannot for a moment be
dispassionately considered by a judicious critic. Nowadays we all know
that the carp are decked in crimson and blue to please their partners,
and that soldiers are dressed in brilliant red to please the æsthetic
authorities who command them from a distance.