INSTINCT
Jules and Emile had put a caterpillar into a glass and brought it to
their uncle, who made it the subject of a little talk to his young
hearers.
“Examine the creature closely,” said he. “Its skin is delicate, so
delicate that even a light touch hurts it; but here on the head, at the
point called the skull, it has the hardness of horn, forming a sort of
cap or helmet which can without injury endure friction with the hard
texture of wood. The head is the part of the creature that opens the
way, and it is therefore protected by armor, while the rest of the
body, as it follows the head, does not need this casing of horn.”
“I understand,” said Emile; “the creature works its way along by
scratching and tunneling with its feet.”
“No, my boy; the feet are not used for boring through wood. The
caterpillar has eight pairs. The first three pairs, or those nearest
the head, have quite a different shape from the others: they are
slender and pointed, and it is they that in the change that takes place
later become the butterfly’s legs, though in doing so they grow much
longer and take another shape. Hence they are called the true legs. The
next four pairs are placed toward the middle of the body, and the last
pair is at the very end. These five pairs bear the name of false legs
because they completely disappear when the caterpillar gives place to
the butterfly or moth. They are short and wide, and are furnished
beneath with numerous little hooks by which the caterpillar clings to
the walls of its abode. The stiff hairs covering the body are also used
for locomotion, the caterpillar wriggling and squirming in its tunnel
somewhat as does the chimney-sweep in helping himself with knees and
back as he makes his way up the inside of a chimney.”
“Then what does the caterpillar use for boring through the wood?” asked
Jules.
“The tool for chipping away the wood consists of two curved fangs or
teeth, almost black, one on each side of the mouth, which open and shut
like a pair of cutting nippers. They are called mandibles and are in
reality jaws or, more properly, teeth which, instead of meeting in a
vertical plane as do ours, come together horizontally or sidewise. For
precision of movement these mandibles are superior to our best cutting
nippers, and for hardness they are almost equal to steel. They seize
the wood, bit by bit, patiently and untiringly; they cut, saw, tear
away a little at a time, and so bore a tunnel just large enough for the
caterpillar to pass through.”
“And what becomes of the wood-dust?” Jules further inquired. “I should
think it would block the way, the passage being so narrow.”
“The wood-dust passes through the creature’s body; the caterpillar eats
it, and after digestion has taken from it the very small amount of
nourishment it contains, it is ejected behind, molded into tiny
pellets. Digestion in a caterpillar is soon accomplished. Just think of
it: wood is an extremely meager fare, and so the worm must keep on
eating its way forward, cutting, gnawing, digesting. To acquire the
fatness necessary for the coming change the creature must have a
good-sized pear-tree limb or lilac trunk to work on.
“The wormhole dust left behind by the boring worm sometimes betrays the
insect to its enemies. Whenever you see any of this dust left by
digestion coming out at some little orifice in the bark of a pear-tree,
apple-tree, or other tree, you may know the borer is at work, and the
branch where he is at work should be cut off immediately, to prevent
more serious harm. If the caterpillar has not gone too far, a pointed
iron wire may be thrust into the opening and an attempt made to kill
the creature in its hole. But as the passage is very winding, this
method is by no means certain of success.”
“Couldn’t the wire be pushed in through another opening?” queried
Jules.
“But, my boy, you don’t suppose the caterpillar is so simple as to make
windows here and there in its dwelling and so make it easy for its
foes, of which it has many besides man, to attack it! If it should take
a fancy, let us say, to go out and get a little fresh air some fine
day, a sparrow might spy it and carry it off as a choice titbit for its
brood under the roof tiles. All these dangers it knows; or, rather, it
guesses them vaguely, for every creature, even to the smallest worm,
knows how to protect itself and preserve its species. Unquestionably it
lacks the reasoning faculty, which belongs only to man; but it none the
less acts as if it reasoned out its own interests with an accuracy that
astounds the thoughtful observer. As a matter of fact, my dear
children, Another has already reasoned for it, and that Other is the
universal Reason in and by whom all live; it is God, the Father of men,
and also the Father of lilacs and of the caterpillars that gnaw them.
The creature knows, then, without ever having learned; it is master of
its art without having been taught; and at the very first trial, with
no experience to rely on, it does admirably the thing it was intended
to do. This gift bestowed at birth, this unfailing inspiration that
guides it in its work, is called instinct.
“In its butterfly state the leopard-moth takes very little food, at the
most a few drops of honey from the opening flowers. Its proboscis, so
slender and so delicate, is fitted to get this food. Now that it no
longer has its strong mandibles, how can the moth imagine that wood is
eatable? Is it possible that it remembers what it liked as a
caterpillar? Who can say? Moreover, how can the moth tell what trees
have wood suitable for the larvæ, when we ourselves must have a certain
degree of education in order to know the commonest varieties? The moth,
with no previous education, never mistakes a plane-tree for a
pear-tree, a box-tree for a lilac, an oak for an elm. Thus the eggs are
always laid on the right sort of tree, never on any other. Where man
might make a mistake, the insect never errs.
“The young larva comes out of the egg. What does the poor little thing
know from experience of the hard trade it is to follow? Nothing,
absolutely nothing. No matter; as soon as it is born it attacks the
wood it rests upon and hollows out a shelter for itself with the least
possible delay. This most urgent business being attended to, it now
leisurely gnaws its way ahead, nibbling a little here and a little
there and shaping its course according to the quality of the wood. The
passage lengthens, increasing in diameter as the creature grows, and
sometimes ascending, sometimes descending, sometimes running
horizontally quite through the trunk or branch. The mass of the wood
may be attacked with little system and without economy, for the larva
is assured of food enough in any event. One precaution, however, it
invariably takes: it never bores through the bark, for fear of
betraying its presence to hostile eyes. But how does the larva, working
in total darkness, know when it is getting near the bark and must turn
back? What gives it the fear it has of showing itself? What makes it so
careful to remain in the heart of the wood and thus avoid the vigilant
sparrow it has never seen? It is instinct, the inspiration that
protects all animal-kind in the fierce battle of life.”