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    4. Strictly Incog

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    Chapter 5
    Previous Chapter
    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.
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