E frequently see, at the ends of pine branches, voluminous
bags of white silk intermixed with leaves. These bags are,
generally, puffed out at the top and narrow at the bottom,
pear-shaped. They are sometimes as large as a person's head.
They are nests where live together a kind of very velvety
caterpillars with red hairs. A family of caterpillars,
coming from the eggs laid by one butterfly, construct a silk
lodging in common. All take part in the work, all spin and
weave in the general interest. The interior of the nest is
divided by thin silk partitions into a number of
compartments. At the large end, sometimes elsewhere, is seen
a wide funnel-shaped opening; it is the large door for
entering and departing. Other doors, smaller, are
distributed here and there. The caterpillars pass the winter
in their nest, well sheltered from bad weather. In summer
they take refuge there at night and during the great heat.
"As soon as it is day, they set out to spread themselves on
the pine and eat the leaves. After eating their fill they
reënter their silk dwelling, sheltered from the heat of
the sun. Now, when they are out on a campaign, be it on the
tree that bears the nest, or on the ground passing from one
pine to another,
 these caterpillars march in a singular
fashion, which has given them the name of processionaries,
because, in fact, they defile in a procession, one after the
other, and in the finest order.
"One, the first come—for amongst them there is perfect
equality—starts on the way and serves as head of the
expedition. A second follows, without a space between; a
third follows the second in the same way; always thus, as
many as there are caterpillars in the nest. The procession,
numbering several hundreds, is now on the march. It defiles
in one line, sometimes straight, sometimes winding, but
always continuous, for each caterpillar that follows touches
with its head the rear end of the preceding caterpillar. The
procession describes on the ground a long and pleasing
garland, which undulates to the right and left with
unceasing variation. When several nests are near together
and their processions happen to meet, the spectacle attains
its highest interest. Then the different living garlands
cross each other, get entangled and disentangled, knotted up
and unknotted, forming the most capricious figures. The
encounter does not lead to confusion. All the caterpillars
of the same file march with a uniform and almost grave step;
not one hastens to get before the others, not one remains
behind, not one makes a mistake in the procession. Each one
keeps its rank and scrupulously regulates its march by the
one that precedes it. The file-leader of the troop directs
the evolutions. When it turns to the right, all the
caterpillars of the same line, one after the other, turn to
the right; when it turns to the left,
 all, one after the
other, turn to the left. If it stops, the whole procession
stops, but not simultaneously; the second caterpillar first,
then the third, fourth, fifth, and so on until the last.
They would be called well-trained troops that, when defiling
in order, stop at the word of command and close their ranks.
"The expedition, simply a promenade, or a journey in search
of provisions, is now finished. They have gone far away from
their nest. It is time to go home. How can they find it,
through the grass and underbrush, and over all the obstacles
of the road they have just traveled? Will they let
themselves be guided by sight, obstructed though it be by
every little tuft of grass; by the sense of smell, which
wafted odors of every sort may put at fault? No, no;
processionary caterpillars have for their guidance in
traveling something better than sight or smell. They have
instinct, which inspires them with infallible resources.
Without taking account of what they do, they call to their
service means that seem dictated by reason. Without doubt,
they do not reason, but they obey the secret impulse of the
eternal Reason, in whom and through whom all live.
"Now, this is what the processionary caterpillars do in
order not to lose their way home again after a distant
expedition. We pave our roads with crushed stone;
caterpillars are more luxurious in their highways: they
spread on their road a carpet of silk, they walk on nothing
but silk. They spin continually on the journey and glue
their silk all along the road. In fact, each caterpillar of
the procession can be seen lowering and raising its head
 alternately. In the first movement, the spinneret, situated
in the lower lip, glues the thread to the road that the
procession is following; in the second, the spinneret lets
the thread run out while the caterpillar is taking several
steps. Then the head is lowered and lifted again, and a
second length of thread is put in place. Each caterpillar
that follows walks on the threads left by the preceding ones
and adds its own thread to the silk, so that in all its
length the road passed over is carpeted with a silky ribbon.
It is by following this ribbon conductor that the
processionaries get back to their home without ever losing
their way, however tortuous the road may be.
"If one wishes to embarrass the procession, it suffices to
pass the finger over the track so as to cut the silk road.
The procession stops before the cut with every indication of
fear and mistrust. Shall they go on? Shall they not go on?
The heads rise and fall in anxious quest of the conductor
threads. At last, one caterpillar bolder than the others, or
perhaps more impatient, crosses the bad place and stretches
its thread from one end of the cut to the other. A second,
without hesitating, passes over on the thread left by the
first, and in passing adds its own thread to the bridge. The
others in turn all do the same. Soon the broken road is
repaired and the defile of the procession continues.
"The processionary caterpillar of the oak marches in another
way. It is covered with white hairs turned back and very
long. One nest contains from seven to eight hundred
individuals. When an
expe-  dition is decided on, a caterpillar
leaves the nest and pauses at a certain distance to give the
others time to arrange themselves in rank and file and form
a battalion. This first caterpillar has to start the march.
Following it, others place themselves, not one after
another, like the processionaries of the pine, but in rows
of two, three, four, and more. The troop, completed, begins
to move in obedience to the evolutions of its file-leader,
which always marches alone at the head of the legion, while
the other caterpillars advance several abreast, dressing
their ranks in perfect order. The first ranks of the army
corps are always arranged in wedge formation, because of the
gradual increase in the number of caterpillars composing it;
the remainder are more or less expanded in different places.
There are sometimes rows of from fifteen to twenty
caterpillars marching in step, like well-trained soldiers,
so that the head of one is never beyond the head of another.
Of course the troop carpets its road with silk as it
marches, so as to find its way back to its nest.
"The processionaries, especially those of the oak, retire to
their nests to slough their skins, and these nests finally
become filled with a fine dust of broken hairs. When you
touch these nests, the dust of the hairs sticks to your
hands and face, and causes an inflammation that lasts
several days if the skin is delicate. One has only to stand
at the foot of an oak where the processionaries have
established themselves, to receive the irritating dust blown
by the wind, and to feel a smart itching."
"What a pity the processionaries have those
hairs!" Jules exclaimed. "If they
"If they hadn't Jules would much like to see the
caterpillars' procession. Never mind; after all, the danger
is not so great. And then, if one had to scratch one's self
a little, it would not be a serious matter. Besides, we will
turn our attention to the processionary of the pine, less to
be feared than that of the oak. At the warmest part of the
day we will go and look for a caterpillars' nest in the pine
wood; but Jules and I will go alone. It would be too hot for
Emile and Claire."