“WE 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 re?nter 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; and 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 ............