THE PINE CATERPILLAR
In my piece of waste ground stand some pine-trees. Every year the
Caterpillar takes possession of them and spins his great purses in
their branches. To protect the pine-needles, which are horribly eaten,
I have to destroy the nests each winter with a long forked stick.
You hungry little Caterpillars, if I let you have your way, I should
soon be robbed of the murmur of my once so leafy pines. But I am going
to make a compact with you. You have a story to tell. Tell it to me;
and for a year, for two years or longer, until I know more or less
about it, I will leave you undisturbed.
The result of my compact with the Caterpillars is that I soon have
some thirty nests within a few steps of my door. With such treasures
daily before my eyes, I cannot help seeing the Pine Caterpillar’s
story unfolded at full length. These Caterpillars are also called the
Processionaries, because they always go abroad in a procession, one
following closely after the other.
[Illustration]
First of all, the egg. During the first half of August, if we look at
the lower branches of the pines, we shall discover, here and there
on the foliage, certain little whitish cylinders spotting the dark
green. These are the Pine Moth’s eggs; each cylinder is the cluster
laid by one mother. The cylinder is like a tiny muff about an inch
long and a fifth or sixth of an inch wide, wrapped around the base of
the pine-needles, which are grouped in twos. This muff has a silky
appearance and is white slightly tinted with russet. It is covered with
scales that overlap like the tiles on a roof. The whole thing resembles
somewhat a walnut-catkin that is not yet full-grown.
The scales, soft as velvet to the touch and carefully laid one upon the
other, form a roof that protects the eggs. Not a drop of rain or dew
can penetrate. Where did this soft covering come from? From the mother
Moth; she has stripped a part of her body for her children. Like the
Eider-duck, she has made a warm overcoat for her eggs out of her own
down.
If one removes the scaly fleece with pincers the eggs appear, looking
like little white-enamel beads. There are about three hundred of them
in one cylinder. Quite a family for one mother! They are beautifully
placed, and remind one of a tiny cob of Indian corn. Nobody, young or
old, learned or ignorant, could help exclaiming, on seeing the Pine
Moth’s pretty little spike,
“How handsome!”
And what will strike us most will be not the beautiful enamel pearls,
but the way in which they are put together with such geometrical
regularity. Is it not strange that a tiny Moth should follow the laws
of order? But the more we study nature, the more we realize that there
is order everywhere. It is the beauty of the universe, the same under
every sun, whether the suns be single or many, white or red, blue or
yellow. Why all this regularity in the curve of the petals of a flower,
why all this elegance in the chasings on a Beetle’s wing-cases? Is that
infinite grace, even in the tiniest details, the result of brutal,
uncontrolled forces? It seems hardly likely. Is there not Some One
back of it all, Some One who is a supreme lover of beauty? That would
explain everything.
These are very deep thoughts about a group of Moth-eggs that will
bear a crop of Caterpillars. It cannot be helped. The minute we begin
to investigate the tiniest things in nature, we have to begin asking
“Why?” And science cannot answer us. That is the strange part of it.
The Pine Moth’s eggs hatch in September. If one lifts the scales of
the little muff, one can see black heads appear, which nibble and push
back their coverings. The tiny creatures come out slowly all over the
surface. They are pale yellow, with a black head twice as large as
their body. The first thing they do is to eat the pine-needles on which
their nest was placed; then they fall to on the near-by needles.
From time to time, three or four who have eaten as much as they want
fall into line and walk in step in a little procession. This is
practice for the coming processions. If I disturb them, they sway the
front half of their bodies and wag their heads.
[Illustration: “When winter is near they will build a stronger tent.”]
The next thing they do is to spin a little tent at the place where
their nest was. The tent is a small ball made of gauze, supported on
some leaves. Inside it the Caterpillars take a rest during the hottest
part of the day. In the afternoon they leave this shelter and start
feeding again.
In less than an hour, you see, after coming from the egg, the young
Caterpillar shows what he can do. He eats leaves, he forms processions,
and he spins tents.
In twenty-four hours the little tent has become as large as a
hazel-nut, and in two weeks it is the size of an apple. But it is still
only a temporary summer tent. When winter is near, they will build a
stronger one. In the meantime, the Caterpillars eat the leaves around
which their tent is stretched. Their house gives them at the same time
board and lodging. This is a good arrangement, because it saves them
from going out, and they are so young and so tiny that it is dangerous
for them to go out yet awhile.
When this tent gives way, owing to the Caterpillars having nibbled the
leaves supporting it, the family moves on, like the Arabs, and erects a
new tent higher up on the pine-tree. Sometimes they reach the very top
of the tree.
In the meantime the Caterpillars have changed their dress. They now
wear six little bright red patches on their backs, surrounded with
scarlet bristles. In the midst of these red patches are specks of gold.
The hairs on their sides and underneath are whitish.
In November they begin to build their winter tent high up in the pine
at the tip of a bough. They surround the leaves at the end of the
bough with a network of silk. Leaves and silk together are stronger
than silk alone. By the time it is finished it is as large as a
half-gallon measure and about the shape of an egg, with a sheath over
the supporting branch. In the center of the nest is a milk-white mass
of thickly-woven threads mingled with green leaves. At the top are
round openings, the doors of the house, through which the Caterpillars
go in and out. There is a sort of veranda on top made of threads
stretched from the tips of the leaves projecting from the dome, where
the Caterpillars come and doze in the sun, heaped one upon the other,
with rounded backs. The threads above are an awning, to keep the sun
from being too warm for them.
The inside of the Caterpillars’ nest is not at all a tidy place; it is
full of rags, shreds of the Caterpillars’ skins, and dirt.
The Caterpillars stay in their nest all night, and come out about ten
o’clock in the morning to take the sun on their terrace or veranda.
They spend the whole day there, dozing. Motionless, heaped together,
they steep themselves deliciously in warmth and from time to time
show their bliss by nodding and wagging their heads. At six or seven
o’clock, when it grows dark, the sleepers awake, bestir themselves, and
go their several ways over the surface of the nest.
[Illustration]
Wherever they go, they strengthen the nest or enlarge it by the threads
of silk that come out of their mouths and trail behind them. More green
leaves are taken in, and the tent becomes bigger and bigger. They are
busy doing this for an hour or two every evening. So far, they have
known nothing but summer; but they seem to realize that winter is
coming. They work away at their house with an ardor that seems to say:
“Oh, how nice and warm we shall be in our beds here, nestling one
against the other, when the pine-tree swings aloft its frosted
candelabra! Let us work with a will!”
Yes, Caterpillars, my friends, let us work with a will, great and
small, men and grubs alike, so that we may fall asleep peacefully; you
with the torpor that makes way for your transformation into Moths, we
with that last sleep which breaks off life only to renew it. Let us
work!
After the day’s work comes their dinner. The Caterpillars come down
from the nest and begin on the pine-needles below. It is a magnificent
sight to see the red-coated band lined up in twos and threes on each
needle and in ranks so closely formed that the green sprigs of the
branch bend under the load. The diners, all motionless, all poking
their heads forward, nibble in silence, placidly. Their broad black
foreheads gleam in the rays of my lantern. They eat far into the
night. Then they go back to the nest, where, for a little longer, they
continue spinning on the surface. It is one or two o’clock in the
morning when the last of the band goes indoors.
The Pine Caterpillars eat only three kinds of pine: the Scotch pine,
the maritime pine, and the Aleppo pine; never the leaves of the other
cone-bearing trees, with one exception. In vain I offer them other
foliage from the evergreens in my yard: the spruce, the yew, the
juniper, the cypress. What! Am I asking them, the Pine Caterpillars,
to bite into that? They will take good care not to, in spite of the
tempting resinous smell! They would die of hunger rather than touch
it! One cone-bearing tree and one only is excepted: the cedar. They
will eat the leaves of that. Why the cedar and not the others? I do not
know. The Caterpillar’s stomach is as particular as ours, and has its
secrets.
To guide them as they wander about their tree, the Caterpillars have
their silk ribbon, formed by threads from their mouths. They follow
this on their return. Sometimes they miss it and strike the ribbon made
by another band of Caterpillars. They follow it and reach a strange
dwelling. No matter! There is not the least quarreling between the
owners and the new arrivals. Both go on browsing peacefully, as though
nothing had happened. And all without hesitation, when bedtime comes,
make for the nest, like brothers who have always lived together; all do
some spinning before going to rest, thicken the blanket a little, and
are then swallowed up in the same dormitory. By accidents like these
some nests grow to be very large. Each for all and all for each. So
says the Processionary, who every evening spends his little capital of
silk on enlarging a shelter that is often new to him. What would he do
with his puny skein, if alone? Hardly anything. But there are hundreds
and hundreds of them in the spinning-mill; and the result of their tiny
contributions is a stuff belonging to all, a thick blanket splendidly
warm in winter. In working for himself, each works for the others;
and the others work for him. Lucky Caterpillars that know nothing of
property, the cause of strife!
THE PROCESSIONARIES
There is an old story about a Ram which was thrown into the water from
on board ship, whereupon all the sheep leaped into the sea one after
the other; “for,” says the teller of the story, “it is the nature of
the sheep always to follow the first, wheresoever it goes; which makes
Aristotle mark them for the most silly and foolish animals in the
world.”
The Pine Caterpillars are even more sheeplike than sheep. Where the
first goes all the others go, in a regular string, with not an empty
space between them.
They proceed in single file, each touching with its head the rear of
the one in front of it. No matter how the one in front twists and
turns, the whole procession does the same. Another odd thing: they are
all, you might say, tight-rope walkers; they all follow a silken rail.
The leading Caterpillar dribbles his thread on the path he makes, the
second Caterpillar steps on it and doubles it with his thread; and all
the others add their rope, so that after the procession has passed,
there is left a narrow white ribbon whose dazzling whiteness shimmers
in the sun. This is a sumptuous manner of road-making: we sprinkle our
roads with broken stones and level them by the pressure of a heavy
steam-roller; they lay over their paths a soft satin rail!
[Illustration: “They Proceed in Single File.”]
What is the use of all this luxury? Could they not, like other
Caterpillars, walk about without these costly preparations? I see two
reasons. It is night when the Processionaries go forth to feed, and
they follow a very winding route. They go down one branch, up another,
from the needle to the twig, from the twig to the branch, and so on.
When it is time to go home, they would have hard work to find their way
if it were not for the silken thread they leave behind them. It reminds
one of the story of Theseus (in the “Tanglewood Tales,” or the old
mythologies), who would have been lost in the Cretan labyrinth if it
had not been for the clue of thread which Ariadne gave him.
Sometimes, too, they take longer expeditions by day, marching in
procession for thirty yards or so. They are not looking for food; they
are off on a trip, seeing the world, perhaps looking for a place to
bury themselves later on, in the second stage before they become Moths.
In a walk of this distance, the guiding-thread is very necessary.
The guiding-thread, too, brings them all back home to the nest when
they are separated, hunting for food in the pine-tree. They pick up
their threads, and come hurrying from a host of twigs, from here, from
there, from above, from below, back to the group. So the silk is more
than a road: it is a social bond that keeps all the members of the
community united.
At the head of every procession, long or short, goes the first
Caterpillar, the leader. He is leader only by chance; everything
depends upon the order in which they happen to line up. If the
file should break up, for some reason, and form again, some other
Caterpillar might have first rank. But the leader’s temporary duties
give him airs of his own. While the others follow passively in a close
file, he, the captain, tosses himself about and flings the front of his
body hither and thither. As he marches ahead he seems to be seeking
his way. Does he really explore the country? Does he choose the best
places? Or are his hesitations only the result of the absence of the
guiding-thread the rest follow? Why cannot I read what passes under his
black, shiny skull, so like a drop of tar? To judge by actions, he has
sense enough to recognize very rough places, over-slippery surfaces,
dusty places, and, above all, the threads left by other Caterpillars.
This is all, or nearly all, that my long acquaintance with the
Processionaries has taught me about their brain power.
The processions vary greatly in length. The finest one I ever saw
was twelve or thirteen yards long and numbered about three hundred
Caterpillars, drawn up with absolute precision in a wavy line. If there
were only two in a row, however, the order would still be perfect: the
second touches and follows the first.
I make up my mind to play a trick upon the Caterpillars which have
hatched out in my greenhouse. I wish to arrange their silken track so
that it will join on to itself and form an endless circuit, with no
branch tracks leading from it. Will the Processionaries then go round
and round upon a road that never comes to an end?
Chance makes it easy for me to arrange something of this sort. On the
shelf in my greenhouse in which the nests are planted stand some big
palm vases measuring nearly a yard and a half in circumference at the
top. The Caterpillars often scale the sides and climb up to the molding
which forms a cornice or ledge around the opening. This place suits
them for their processions. It provides me with a circular track all
ready-made.
One day I discover a numerous troop making their way up and gradually
reaching the favorite ledge. Slowly, in single file, the Caterpillars
climb the great vase, mount the ledge, and advance in regular
procession, while others are constantly arriving and continuing the
series. I wait for the string to close up, that is to say, for the
leader, who is following the circular track, to return to the point
from which he started. This happens in a quarter of an hour. I now have
a circle of Caterpillars around the top of the vase.
The next thing is to get rid of the rest of the Caterpillars who are on
their way up and who might disturb the experiment; we must also do away
with all the silken paths that lead from the top of the vase to the
ground. With a thick hair-pencil I sweep away the Caterpillars; with
a big brush I carefully rub down the vase and get rid of every thread
which the Caterpillars have laid on the march. When these preparations
are finished, a curious sight awaits us.
The Caterpillars are going round and round on the ledge at the top
of the vase. They no longer have a leader, because the circle is
continuous; but they do not know this, and each follows the one in
front of him, who he thinks is the leader.
The rail of silk has grown into a narrow ribbon, which the Caterpillars
keep adding to. It has no branches anywhere. Will they walk endlessly
round and round until their strength gives out entirely?
[Illustration]
Old-fashioned scholars were fond of quoting the tale of the Donkey who,
when placed between two bundles of hay, starved to death because he was
unable to decide in favor of either. They slandered the worthy animal.
The Donkey, who is no more foolish than any one else, would feast off
both bundles. Will my Caterpillars show a little of his common-sense?
Will they make up their minds to leave their closed circuit, to swerve
to this side or that? I thought that they would, and I was wrong. I
said to myself:
“The procession will go on turning for some time, for an hour, two
hours perhaps; then the Caterpillars will perceive their mistake. They
will abandon the deceptive road and make their descent somewhere or
other.”
That they should remain up there, hard pressed by hunger and the lack
of shelter, when nothing prevented them from going away, seemed to
me unthinkable foolishness. Facts, however, forced me to accept the
incredible.
The Caterpillars keep on marching round the vase for hours and hours.
As evening comes on, there are more or less lengthy halts; they go
more slowly at times, especially as it grows colder. At ten o’clock in
the evening the walk is little more than a lazy swaying of the body.
Grazing-time comes, when the other Caterpillars come crowding out from
their nests to feast on the pine-needles. The ones on the vase would
gladly take part in the feast; they must have an appetite after a ten
hours’ walk. A branch of pine is not a hand’s breadth away from them.
To reach it they have only to go down the vase; and the poor wretches,
foolish slaves of their ribbon that they are, cannot make up their
minds to do so. At half-past ten I leave them to go to bed; I am sure
that during the night they will come to their senses. At dawn I visit
them again. They are lined up as on the day before, but motionless.
When the air grows a little warmer, they shake off their torpor,
revive, and start walking again in their circle.
Things go on as before during the next day. The following night is very
cold. The poor Caterpillars spend a bad night. I find them clustered
in two heaps on the top of the vase, without any attempt at order.
They have huddled together to keep warm. Perhaps, now that they are
divided into two parts, one of the leaders, not being obliged to follow
a Caterpillar in front of him, will have the sense to break away. I am
delighted to see them lining up by degrees into two distinct files,
with two leaders, free to go where they please. At the sight of their
large black heads swaying anxiously from side to side, I am inclined to
think they will leave the enchanted circle. But I am soon undeceived.
As the ranks fill out, the two sections of the chain meet and the
circle is formed again. Again the Caterpillars march round and round
all day.
The next night is again cold, and the Caterpillars gather in a heap
which overflows both sides of the fatal ribbon. Next morning, when they
awake, some of them who find themselves outside the track actually
follow a leader who climbs to the top of the vase and down the inside.
There are seven of these daring ones. The rest pay no attention to them
and walk round the circle again.
The Caterpillars inside the vase find no food there, and retrace their
steps along their thread to the top, strike the procession again, and
slip back into the ranks.
Another day passes, and another. The sixth day is warm, and for the
first time I see daring leaders, who, drunk with heat, stand on
their hind-legs at the extreme edge of the vase and fling themselves
forward into space. At last one of them decided to take the plunge.
He slips under the ledge and four follow him. They go halfway down
the vase, then their courage fails and they climb up again and rejoin
the procession. But a start has been made and a new track laid. Two
days later, on the eighth day of the experiment, the Caterpillars—now
singly, then in small groups, then again in strings of some length—come
down from the ledge by starting on this fresh path. At sunset the last
of the Caterpillars is back in the nest at the foot.
I figure that they have walked for eighty-four hours, and covered a
good deal more than a quarter of a mile while traveling in the circle.
It was only the disorder due to the cold nights that ever set them off
the track and back to safety. Poor, stupid Caterpillars! People are
fond of saying that animals can reason, but there are no beginnings of
a reasoning power to be seen in them.
[Illustration]
THE CATERPILLARS AS WEATHER PROPHETS
In January the Pine Caterpillar sheds his skin for the second time. He
is not nearly so pretty afterwards, but he has gained some new organs
which are very useful. The hairs on the middle of his back are now
of a dull reddish color, made paler still by many long white hairs
mixed in with them. This faded costume has an odd feature. On the back
may be seen eight gashes, like mouths, which open and close at the
Caterpillar’s will. When the mouths are open there appears in each of
them a little swelling, which seems extremely sensitive, for at the
slightest irritation it goes in again.
What is the use of these queer mouths and tumors, as we call the little
swellings? Certainly not to breathe with, for no one, not even a
Caterpillar, breathes from the middle of his back. Let us consider the
habits of the Pine Caterpillar, and perhaps we shall find out.
The Pine Caterpillar is most active during the winter, and at night.
But if the north wind blow too violently, if the cold be too piercing,
if it snow, or rain, or if the mist thicken into an icy drizzle, the
Caterpillars prudently stay at home, sheltering under their waterproof
tent.
It would be convenient to foresee these disagreeable weather
conditions. The Caterpillar dreads them. A drop of rain sets him in a
flutter; a snowflake exasperates him. To start for the grazing-grounds
at dark of night, in uncertain weather, would be dangerous, for the
procession goes some distance and travels slowly. The flock would have
a bad time of it before regaining shelter, if they were caught in a
sudden storm, such as are frequent in the bad season of the year. Can
the Pine Caterpillar possibly be able to foretell the weather? Let me
tell how I came to suspect this.
One night some friends came to see my Caterpillars in the greenhouse
start on their nightly pilgrimage. We waited till nine o’clock, then
went in. But, but ... what is this? Not a Caterpillar outside the
nests! Last night and on the nights before they came out in countless
numbers; to-night not one is to be seen. We waited till ten o’clock,
till eleven, till midnight. Then, very much mortified, I had to send my
friends away.
Next day I found that it had rained in the night and again in
the morning, and that there was snow on the mountains. Had the
Caterpillars, more sensitive than any of us to atmospheric changes,
refused to venture out because they had known what was going to happen?
After all, why not? I thought I would keep on observing them.
I found that whenever the weather chart in the newspaper announced a
coming depression of the atmosphere, such as is made by storms, my
greenhouse Caterpillars stayed at home, though neither rain, snow, nor
cold could affect them in their indoor shelter. Sometimes they foretold
the storm two days ahead. Their gift for scenting bad weather very soon
won the confidence of the household. When we had to go into town to buy
provisions, we used to consult our Caterpillars the night before; and
according to what they did, we went or stayed at home.
The second dress of the Pine Caterpillar, therefore, seems to bring
with it the power to foretell the weather. And this power is probably
given by the wide mouths, which yawn open to sample the air from time
to time and to give a warning of the sudden storm.
THE PINE MOTH
When March comes, the Caterpillars leave their nest and their pine-tree
and go on their final trip. On the twentieth of March I spent a whole
morning watching a file about three yards long, containing about a
hundred of the Caterpillars, now much faded as to their coats. The
procession toils grimly along, up and down over the uneven ground. Then
it breaks into groups, which halt and form independent processions.
They have important business on hand. After two hours or so of
marching, the little procession reaches the foot of a wall, where the
soil is powdery, very dry, and easy to burrow in. The Caterpillar at
the head of the row explores, and digs a little, as if to find out
the nature of the ground. The others, trusting their leader, follow
him blindly. Whatever he decides will be adopted by all. Finally the
leading Caterpillar finds a spot he likes; he stops, and the others
break up into a swarming heap. All their backs are joggling pell-mell;
all their feet are raking; all their jaws are digging the soil. Little
by little, they make a hole in which to bury themselves. For some time
to come the tunneled soil cracks and rises and covers itself with
little mole-hills; then all is still. The Caterpillars have descended
to a depth of three inches, and are weaving, or about to weave, their
cocoons.
Two weeks later I dug down and found them there, wrapped in scanty
white silk, soiled with dirt. Sometimes, if the soil permits, they bury
themselves as deep as nine inches.
How, then, does the Moth, that delicate creature, with her flimsy wings
and sweeping antennæ-plumes, make her way above ground? She does not
appear till the end of July or in August. By that time the soil is
hard, having been beaten down by the rain and baked by the sun. Never
could a Moth break her way through unless she had tools for the purpose
and were dressed with great simplicity.
[Illustration]
From some cocoons that I kept in test-tubes in my laboratory I found
that the Pine Moth, on coming out of the cocoon, has her finery bundled
up. She looks like a cylinder with rounded ends. The wings are pressed
against her breast like narrow scarfs; the antennæ have not yet
unfolded their plumes and are turned back along the Moth’s sides. Her
hair fleece is laid flat, pointing backwards. Her legs alone are free,
to help her through the soil.
She needs even more preparation, though, to bore her hole. If you pass
the tip of your finger over her head you will feel a few very rough
wrinkles. The magnifying-glass shows us that these are hard scales, of
which the longest and strongest is the top one, in the middle of her
forehead. There you have the center-bit of her boring-tool. I see the
Moths in the sand in my test-tubes butting with their heads, jerking
now in one direction, now in another. They are boring into the sand.
By the following day they will have bored a shaft ten inches long and
reached the surface.
When at last the Moth reaches the surface, she slowly spreads her
bunched wings, extends her antennæ, and puffs out her fleece. She
is all dressed now, as nicely as she can be. To be sure, she is
not the most brilliant of our Moths, but she looks very well. Her
upper wings are gray, striped with a few crinkly brown streaks; her
under-wings white; throat covered with thick gray fur; abdomen clad in
bright-russet velvet. The tip end of her body shines like pale gold.
At first sight it looks bare, but it is not: it is covered with tiny
scales, so close together that they look like one piece.
There is something interesting about these scales. However gently we
touch them with the point of a needle, they fly off in great numbers.
This is the golden fleece of which the mother robs herself to make the
nest or muff for her eggs at the base of the pine-needles which we
spoke of at the beginning of the story.
[Illustration]