PROTECTIVE RESEMBLANCE IN NATURE—SPIDERS THAT LOOK LIKE ANTS—A
TRAP TO CATCH A BUTTERFLY—FALSE DEVOTEES—LEAF, STICK, AND
GRASS-RESEMBLING INSECTS—“CUCULLUS NON FACIT MONACHUM.”
In previous chapters we have seen how spiders are preyed upon in a
peculiar way, and for a special purpose, by various species of wasps,
and how, in a more general manner, they fall victims to ants. There
are spiders, however, who escape both wasps and ants, as well as other
enemies, against which they are not strong enough to contend, not by
running away, merely, or concealing themselves, which are ordinary
methods, but by another plan not quite so common in nature, which some
people think is only resorted to by ourselves. We, for instance, if we
have committed a robbery or anything of that sort, and it is known that
we did it, disguise ourselves like somebody else—it does not matter
who—so as to get to Spain or America, or anywhere we think best, without
being recognised. Or sometimes we do the disguising first, and get the
money in that way, dressing up to resemble some person that we pretend to
be, or someone in his or her class of life—the nobility mostly—and living
in the way that they would do, so that we take people in right and left,
and they trust us in a way that they would never think of doing if they
knew that we were only poor, honest people who paid our way, and made
no sort of dash or show. Now this is just what some animals, especially
insects, do, only whereas we have to dress up for each occasion, and can
assume different disguises, they are always disguised in the same way,
and whereas we know what we are doing, and why we are doing it, they know
nothing at all about it, which last gives them a great advantage, since
even the finest acting does not quite come up to nature. Some creatures,
in fact, are cheats all their lives through. Their “whole life is a
lie,” as one of the characters in one of Scott’s novels said once, a
long time ago, and as thousands of very different sorts of characters in
very different kinds of novels, have been saying to or of one another or
themselves—or words to that effect—ever since.
And now for examples, which is the only way of getting to understand
anything, unless it is very simple indeed. To begin with spiders. There
are some that look exactly like ants, so that anyone seeing them for
the first time would think that they were ants, and would only find out
that they were not, but spiders, by degrees, and perhaps not at all if
he were not something of an entomologist. Ants, like all other insects,
have six legs, whereas spiders, which are not insects at all, have eight.
But the spider, by holding up one of its anterior pair of legs, either
the first or the second pair, and bending or pointing them to suit
the kind of ant it resembles, makes them look like a pair of antennæ,
springing not from its body but from the head. The head itself looks much
more like an ant’s than a spider’s, and this is still more—or still
more remarkably—the case with the body, which is lengthened in various
degrees, and shaped in various ways, in accordance with that of the model
on which the make-up is founded.
But this is not all, or enough. However much the spider might look like
the ants that it lived amongst, yet if it did not move in the same kind
of way that they do it would be detected, and in consequence devoured.
Spiders do not walk or run about like ants, not, that is to say, with
the same sort of mannerisms that they have. Some of them jump, which is
a thing that ants never do, and all ants, when in search of booty, move
in a funny little zigzagging way from side to side, which gives them a
greater chance of finding things than they would have by going straight
forward. Now it is just in this way that some of these ant-like spiders
habitually walk, and they do not jump any more than the ants themselves,
even though they may happen to belong to a family of jumping spiders.
Again, when they eat anything, instead of sitting still, to do it, which
is what spiders generally do, they keep pulling the morsel, which is
generally some live thing, about, as though to divide it into parts, to
be carried to the nest separately, which is what ants often do; and all
the while they keep moving the two legs which look like a pair of antennæ
just in the way in which it is proper for antennæ to move, sometimes
tapping their prey with them, and at other times waving them about. No
wonder then that the ants are taken in, for, to the boot of all these
resemblances, the spider is of the same size and colour as themselves.
The result of it all is, of course, that not an ant of them ever thinks
of molesting the spider. He would be a nice tasty morsel for them if they
only knew it, and as he is soft and they are hard, they would have no
difficulty in overcoming him, even if it were only one to one, instead
of one to twenty or more. But as they only see one of themselves running
about—and, for my part, I think the spider must feel like an ant, as well
as look like one—it never enters their head to attack him, or even not to
be polite, for ants of the same nest are very polite to one another.
But here all sorts of questions arise, which, as far as I know, have not
yet been answered, and I think that the ways of these spiders ought to be
more closely observed. Ants of the same nest, indeed, are quite friendly
one with another, but this is not the case if they belong to different
nests, whilst there is nothing but hostility, as a rule, between ants
of different species. Moreover, one ant can always tell, by some means
which we do not yet quite understand, whether another one belongs to
its own community or not, and if it does not there is generally a fight
between them, unless one of the two runs away. It would seem, therefore,
as if, for its disguise to be of much use to the spider, it would have to
keep not only with one species, but with one special community of ants,
and even then it ought to be found out, unless it lives with them as a
parasite in their nest, as some insects and other creatures do. Is this
the case, or does the spider take care not to come into actual contact
with the ants, so that just by looking like one at a little distance,
it is left alone? But, even so, it would be only one species of ant
that would be inclined to let him alone, and as other species would be
hostile to the one he resembled, one can imagine inconveniences as well
as benefits arising through the disguise. For the above reasons I think
it would be very interesting to find out a little more about the habits
of these ant-resembling spiders. Of course if they preyed upon the ants
they resembled, the thing would be easy to understand. But this, as has
already been said or implied, is not the case.
Other kinds of spiders are protected in the same way by resembling
different kinds of things, which are not good to eat, and as, in this
way, they are saved not only from ants, but from all sorts of other
creatures, as well,—from all those, for instance, that prey upon
ants—this seems to me a much better kind of disguise. One of these
spiders lives in Madagascar, and has the most peculiar-shaped body
that one can imagine. At the top it runs up into a sort of pyramid,
starting from a rounded base and being higher at one side than another,
whilst round about it there are several smaller pyramids, or spikey
protuberances, quite babies compared to the large one. On a table,
perhaps, or in that horrid thing, a cabinet, it might be difficult to say
what this spider was intended to look like, but when it sits motionless,
according to its habit, on the branch of a tree, it is impossible to
distinguish it from one of those woody knots which often form themselves
on the bark, and which the eye rests on without particularly noticing.
Another kind, common in Wisconsin, lives upon the cedar trees, which are
a common feature—and a very picturesque one—of the country. They are
covered with lichens, and so much does this spider, in its coloration and
markings, resemble a lichen, itself, that when it sits still amongst them
the eye is unable to pick it out from its surroundings.
But all this is as nothing compared to a Javanese spider, the whole of
whose energies seem bent to make itself into a living facsimile of so
mean an object as a bird-dropping. To do this, it lies on its back upon a
leaf, over some part of which it has previously spread a film-like web,
which itself plays a part in the deception. “Such excreta,” says Mr.
Fobes, the discoverer of this wonderful spider, and who was, himself,
taken in by it, “consist of a central and denser portion of a pure white
chalk-like colour streaked, here and there, with black and surrounded by
a thin border of the dried-up, more fluid part.” The filmy web spread
irregularly over the leaf, presents this latter appearance, whilst the
spider itself, having a chalky-white abdomen and black legs, which, as
it lies, are crossed over it, exactly resembles the solid mass in the
centre of it. In the previous cases that we have been considering, the
resemblance is of a protective nature—this, at least, is what seems
more specially aimed at—but here the design is darker and deeper. Many
butterflies—creatures typical of beauty generally—as if resolved to
carry on the allegory, are accustomed to feed upon ordure. One of them,
fluttering through the leaves of the tropical forest, perceives, as she
thinks, a rich banquet spread out before her, and descending, in all
her radiant and ethereal beauty, to enjoy it, is caught and feasted on
herself.
Here, then, we have an aggressive, as well as a protective,
resemblance—for, no doubt, the two are combined—of which principle we
have another example in a certain mantis of India, which resembles,
in a manner equally deceptive, if not quite so perfect, a more
attractive object, namely, a flower. Most of us have seen pictures of
the ordinary green praying mantis, a curious kind of insect, allied
to the grasshoppers, that has received its name owing to its habit
of sitting motionless with the fore part of its body raised, and its
fore legs extended, as though it were praying. Really, however, it is
waiting for its prey, which, when it approaches, it cuts to pieces by
pressing together, as though it were shutting a knife, the flattened
and blade-like joints of the legs it has held out so holily; first,
of course, having got the victim between them. The mantis in question
does not look quite like the praying one. Instead of rearing itself
upright, it sits flat on the leaf, and its body is not green, but pink.
Being rounded, it passes for the centre of a flower, whilst the legs,
which diverge from it at different angles, and are flattened in the
most extraordinary manner, bear a still more striking resemblance to
the petals. Sitting thus, a flower amongst flowers, it is approached by
many insects which, too late, discover the real nature of that somewhat
strange-looking blossom.
Here, then, we have a flower-insect. Stick-insects—walking-stick insects
as we call them—or grass-insects, are more common. They are especially
abundant in Central Africa. Anyone who sees one of these creatures for
the first time is infallibly taken in by them, though he may have read
about them often, and made up his mind not to be. He is strengthening
himself, perhaps, in this resolution, at the moment when, having at last
got to the country where they abound, he happens to be brushing away,
with his hand, a small wisp of hay or dry grass that he sees clinging to
his coat. But that wisp of hay is the very insect he has set himself to
recognise, but which now, even when his native servants point it out to
him and tell him what it is, he cannot for the life of him make out to
be anything but what it looks like. It is just a slight stem of yellow,
withered grass, from which six still slighter pieces hang, at intervals,
in pairs. Bend the stem as you will, and twist the bits that hang from
it how you like, they all stay just as you put them, as long as they
have anything to rest against. But if you take the thing, at any point,
between your thumb and finger, and hold it in the air, then the other
parts of it will either remain stiff or dangle down, just as you would
expect them to do, if it were a piece of grass that you held. The insect
seems jointed everywhere, so that, what with this, and the thinness and
ridiculous length of its body and all its legs, it does not even look
like a healthy growing grass, but only a long, thin bit that has first
been broken off, then broken again, in all sorts of places, and, finally,
crushed up, squeezed and crumpled together in the hand. Yet the insect
which it really is, has a head, eyes, antennæ, thorax, abdomen, and all
the internal organs like any other one, and it breathes, sleeps, eats,
and digests upon just the same principles. There are thousands of these
wonderful grass-insects, and almost as many different species of them.
All about, wherever the grass springs up in patches, amidst the forests
of equatorial Africa, they form, as it were, a sort of second animal
crop, living amongst the vegetable one and indistinguishable from it.
When they leap from one stem to another, then, all at once, they are
seen; but the instant they alight they become invisible again, vanishing
under one’s very eyes, whilst one looks at them, as if by magic. What is
most wonderful is that as the tintings of the true grasses change with
the season, so do those of the false ones that cling to them. From the
bright, vivid green of the fresh spring crops, through the later darker
greens, and the golds and reds of autumn, all is mimicked, the one change
keeps pace with the other, but whether it is a sequence of different
imitative creatures—like the rotation of crops—or whether it is not the
species, but only their colours, which change, does not appear to be
certain, though, probably, it is the latter.
Other insects imitate mosses or lichens, whilst a still greater number,
perhaps, are the counterparts of all kinds of leaves—from the fresh
young green ones to those which are sere and yellow. To these belong the
mantises which we have just been talking about, besides a whole host of
locusts and grasshoppers. One of these latter was seen by Mr. Belt, in
Nicaragua, standing perfectly still in the midst of an army of foraging
ants, numbers of which kept passing over its body, and would at once have
torn it to pieces, had they had the smallest idea that it was not what it
pretended to be. This locust had wings, like others of its family, and
could easily, by their aid, have got away from the ants. This, however,
would not have saved its life, for the air and surrounding trees were
full of birds that were busily engaged in catching such insects as the
ants put up. Knowing, therefore, that it would only be flying from danger
to certain death, it preferred, or, rather, its instinct taught it, to
stay and brave the former, which it might do with a very fair chance,
though not quite a certainty, of success. That there was no choice in the
matter we may, I think, assume, because with all these creatures that
imitate still life, there is a strong instinct to be still themselves
whenever there is cause for alarm—and indeed generally, as long as moving
can be dispensed with. This is, indeed, a part of the deception, since it
is obvious to the meanest capacity of bird or predaceous insect, that a
leaf, for instance, that walks about, cannot really be a leaf.
Neither can it, when it, all at once, comes off its stalk and begins to
fly about, in the shape of a butterfly, which is what happens, sometimes,
in India and the Malay Archipelago, as we shall immediately see. In
these countries there is a butterfly that belongs to the same family as
our own purple emperor, and, as far as the upper surface of its wings
is concerned, it is a purple emperor, and so looks like one, when it
flies. But as soon as it settles, it becomes a leaf, for then it raises
its wings above its back, in the way butterflies do, so that only their
under surface is seen, which is as like a dry brown leaf as anything
that is not one can be. The shape is exact, from the extreme point, or
tip, of the upper wing, to the little swallow tail at the end of the
lower one, which last just touches the stem that the butterfly clings
on, and makes the stalk of the leaf. Between the tip and the stalk there
runs a well-marked dark line, which answers very well for the leaf’s
mid-rib, whilst on each side of it thinner lines are traced, representing
the lateral veins. The slender legs of the butterfly, as it sits on the
stalk, are hardly to be seen, and its head lies just hidden between
the margins of the wings. The leaves of the bush on which it has gone
down are of the same shape and colour as itself, for it takes care not
to settle amidst surroundings with which it would not be in harmony. A
bird, therefore, that has pursued this brilliant blue butterfly into a
bush, where it disappears, is completely baffled; and so, too, is a grave
scientific gentleman with a butterfly-net in his hand.
The above, I believe, is the best example known of a butterfly that
escapes its enemies by looking like a leaf, or any other inanimate
object; but there are others where the take-in is of a still more curious
and unexpected kind. Certain butterflies have bitter juices in their
bodies, and for this reason are let alone by birds and other enemies. As
a consequence, other butterflies belonging to quite different families,
have taken to mimicking them—just as if _they_ were leaves or sticks or
grasses—so that, being mistaken for them, they are let alone too. If they
were not so mistaken, they would be eaten at once—or at least whenever
they could be caught—for their juices are very nice indeed. What seems
still more extraordinary is that, in some cases, the nasty butterfly
is mimicked only by the female of the nice one, and not by the male.
Thus there is a butterfly in Africa, the male of which is a beautiful
swallow-tail, but the female has no tails to her wings, and both in shape
and colouring she is just like another butterfly, not nearly so handsome,
and which is not a swallow-tail at all. What can be the reason of this?
What can account for this favouritism in Nature?—for that is what it
seems like. Why should only the nice-tasting female be protected, and
not the equally nice-tasting male? But the male, it appears, can fly
faster, and he is not bothered by having to lay eggs, like the female.
The female, with eggs in her body, is heavier than he, and whilst she is
laying them she has to sit still. This is the explanation generally given
for a fact so remarkable. I confess that I don’t feel quite satisfied
with it, but it is difficult to think of a better one. At any rate, there
are the facts. Butterflies mimic each other, and pretend to belong to
families which they really don’t belong to—just as adventurers do.
But it may be said, how can one tell which is which, or, if two
butterflies look exactly alike, how can we tell that they do belong to
two families, and not to one and the same? But if one dissects a leaf-,
or a walking-stick-insect, one does not find that it is like a leaf, or a
piece of twig, inside, and just in the same way, though the difference is
not so great, the two butterflies that look so much alike, are found to
differ, on dissection. The internal organs of the mimicking kind have not
been changed in the same way that its colouring and shape have been—for
that would have done it no good—and then, again, it is not quite exactly
like the other one; there is some difference, a little more, perhaps,
than that between Tweedledum and Tweedledee, which would be enough for an
entomologist, when he had the two on a table, to be able to tell.
It is not only amongst insects that these curious cases of beneficial
resemblance are to be found, that creatures live, as it were, a false
life, and are not what they seem to be. The device, indeed, is not so
frequently resorted to in the case of any other order of animals, and
when it is, it is not, as a rule, so marked—not of such a definite nature
as with insects, and some other of the smaller class of creatures,
but still the principle is there. We have seen the case of the mantis
pretending, as it were, to be a flower. There is a certain lizard that
does much the same thing, for the skin at the angle of its mouth, on each
side, is puckered up into a little red flower, just like one that grows
in the sand, where it lives. Insects, thinking to come to the flower,
come to the lizard’s mouth instead, and are soon gobbled up. Insects
are things which often fly into manifest danger, but still, if they saw
the lizard they would be less likely to come to the flower. But now
this lizard’s body is exactly the colour of the sand that it lies in,
so that it can hardly be seen, and this sort of general resemblance is
much more common amongst birds and mammalia than the more special ones
that we have been considering. I do not, indeed, know any case of one
quadruped escaping destruction, by being mistaken for another, or for a
rock or tree, but amongst birds there are just a few instances of this.
In the Malay Archipelago, for instance, there are some loud, noisy birds
which are called “Friar-birds,” because some of the feathers on their
necks curl up over their heads, like a friar’s cape or cowl. They have
powerful beaks and claws, which they know how to use, and, as they fly
about in flocks, they are very well able to take care of themselves.
There are different species of these friar-birds on each of the larger
islands, and in each of these islands—flying in the same flock with
them—is a bird of a quite different family, and as timid and retiring as
the others are bold and aggressive. Orioles these attendant birds are,
and the typical oriole is as different from a friar-bird in appearance as
it is in disposition. But these particular ones resemble them so exactly
that they have been mistaken for friar-birds by scientific gentlemen,
with the two together in their hands, and have even got mixed up with
them in scientific works—flying with them still, through those dry, dead
leaves, as though they were the living forests of their native land. Thus
in a great scientific French book, called _Voyage de l’Astrolabe_, an
oriole of Bouru is both described and figured as a friar-bird, keeping
up the joke, or the fiction, to the very last. However, as far as that
is concerned, I have no doubt that the oriole thinks he really is a
friar-bird, or, at least, feels as if he was one, which would come to
much the same thing.
When first these cases of imitation, or mimicry as they are called,
began to be noticed,[11] nobody could tell what to make of them. It
seemed plain that one animal could not purposely make itself like another
one—or like a twig or a flower—in the way that an actor dresses up to
represent some character on the stage. But how, then, had such marvellous
resemblances been brought about? Chance seemed quite out of the question,
but nobody had any better explanation to give. The whole thing was a
mystery. Gradually, however, the subject came to be better understood.
One thing was clear: that the animal—or one of the animals—presenting
this extraordinary likeness was always benefited by it. At last came
Darwin, who explained everything by natural selection, the principle of
which is this, that as no two individuals of any species are born quite
alike, some must be born with some sort of an advantage over others, and
as these would live longer, and leave a greater number of descendants to
inherit this advantage—whatever it might be—all living creatures must,
gradually, be getting better and better adapted for the kind of life they
have to lead. Supposing, therefore, that two different creatures, living
in the same country, had some slight resemblance to one another—and
this would not be wonderful—then if this resemblance was an advantage
to one of them, it would gradually get more and more like the other,
because those individuals that were less like it would get killed off
sooner, whilst the others would live longer and leave a greater number
of offspring, to carry on the likeness. Those orioles, for instance—to
take our last example—which least resembled the friar-birds, would get
soonest killed by hawks and kites, whilst those that most resembled them
would be most let alone, and so they would lay more eggs, and rear more
young birds, and of these young orioles, some would be even more like
the friar-birds than their parents, and so it would go on. The gradually
increasing resemblance would be like a portrait that was always being
painted and painted, and having finishing touches put to it, without
ever being quite finished—an eternal sitter with an eternal artist
in front of him; for the sitter, too, would change as time went on,
and as he did, so would his portrait have to. This is how Nature, the
great artist, paints her portraits, so that when, in speaking of these
cases, we say that one creature mimics another we really mean something
quite different. Still, mimic, we are told, though it conveys a wrong
meaning, is the best word to use, because with it we can express this
wrong meaning in so many different ways, having at our disposal “the
convenient series of words—mimic, mimicry, mimetic, mimicker, mimicked,
mimicking.” So we should not call something that is white, white, if,
with more flexibility, we could describe it as black—and this, indeed,
with the converse, is a principle very much in vogue. The curious thing
is, however, that when the likeness is between some creature and a plant
or inanimate object, scientists do not say that the former mimics the
latter, but that it resembles it. They can put up with the right word
then, but not, it appears, in the other case. Yet there is no essential
distinction between the two, and the process by which each has been
brought about, is identical. So, as one butterfly, say, does really
resemble another, but does not really mimic it, why cannot learned
gentlemen use the right word here too, instead of speaking a language
which neither accords with the fact, nor expresses their real meaning?
Even if it does come more pat to describe a thing badly, is it not,
nevertheless, better to describe it well? So I say, with Hotspur—
“Oh, while you live tell truth and shame the devil.”
For my part I think it is only permissible to use the word “mimic,” in
this relation, in order to give a vivid impression, not indeed of the
thing, but of what the thing seems to be—to arouse interest in it, in
fact, which is why I have done so here. But when the process is known the
word had better be dropped—at least, in works that really profess to be
scientific. This, of course, does not.