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,
"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
"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
expedition 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
"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 detestable hairs!" Jules exclaimed. "If they hadn't—"
"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."