The Life of the Caterpillar

by Jean-Henri Fabre

THE PINE PROCESSIONARY: THE NEST; THE COMMUNITY

November arrives, however, bringing cold weather; the time has come to build the stout winter tabernacle. High up in the pine the tip of a bough is chosen, with suitably close-packed and convergent leaves. The spinners surround it with a spreading network, which bends the adjacent leaves a little nearer and ends by incorporating them into the fabric. In this way they obtain an enclosure half silk, half leaves, capable of withstanding the inclemencies of the weather.

Early in December the work has increased to the size of a man’s two fists or more. In its ultimate perfection, it attains a volume of nearly half a gallon by the end of winter.

It is roughly egg-shaped, tapering to a certain length below and extended into a sheath which envelops the supporting branch. The origin of this silky extension is as follows: every evening between seven and nine o’clock, [[28]]weather permitting, the caterpillars leave the nest and go down the bare part of the bough which forms the pole of the tent. The road is broad, for this axis is sometimes as wide as the neck of a claret-bottle. The descent is accomplished without any attempt at order and always slowly, so much so that the first caterpillars to come out have not yet dispersed before they are caught up by the others. The branch is thus covered by a continuous bark of caterpillars, made up of the whole community, which gradually divides into squads and disperses to this side and that on the nearest branches to crop their leaves. Now not one of the caterpillars moves a step without working his spinneret. Therefore the broad downward path, which on the way back will be the ascending path, is covered, as the result of constant traffic, with a multitude of threads forming an unbroken sheath.

It is obvious that this sheath, in which each caterpillar, passing backwards and forwards on his nocturnal rambles, leaves a double thread, is not an indicator laid down with the sole object of simplifying the journey back to the nest: a mere ribbon would be enough for that. Its use might well be to strengthen the [[29]]edifice, to give it deeper foundations and to join it by a multitude of cables to the steady branch.

The whole thing thus consists, above, of the home distended into an ovoid and, below, of the stalk, the sheath surrounding the support and adding its resistance to that of the numerous other fastenings.

Each nest that has not yet had its shape altered by the prolonged residence of the caterpillars shows in the centre a bulky, milk-white shell, with around it a wrapper of diaphanous gauze. The central mass, formed of thickly-woven threads, has for a wall a thick quilt into which are absorbed, as supports, numbers of leaves, green and intact. The thickness of this wall may be anything up to three-quarters of an inch.

At the top of the dome are round openings, varying greatly in number and distribution, as wide across as an ordinary lead-pencil. These are the doors of the house, through which the caterpillars go in and out. All around the shell are projecting leaves, which the insects’ teeth have respected. From the tip of each leaf there radiate, in graceful, undulating curves, threads which, loosely interlaced, form [[30]]a light tent, a spacious verandah of careful workmanship, especially in the upper part. Here we find a broad terrace on which, in the daytime, the caterpillars come and doze in the sun, heaped one upon the other, with rounded backs. The network stretching overhead does duty as an awning: it moderates the heat of the sun’s rays; it also saves the sleepers from a fall when the bough rocks in the wind.

Let us take our scissors and rip open the nest from end to end longitudinally. A wide window opens and allows us to see the arrangement of the inside. The first thing to strike us is that the leaves contained in the enclosure are intact and quite sound. The young caterpillars in their temporary establishments gnaw the leaves within the silken wrapper to death; they thus have their larder stocked for a few days without having to quit their shelter in bad weather, a condition made necessary by their weakness. When they grow stronger and start working on their winter home, they are very careful not to touch the leaves. Why these new scruples?

The reason is evident. If bruised, those leaves, the framework of the house, would [[31]]very soon wither and then be blown off with the first breath of wind. The silken purse, torn from its base, would collapse. On the other hand, if the leaves are respected, they remain vigorous and furnish a stout support against the assaults of winter. A solid fastening is superfluous for the summer tent, which lasts but a day; it is indispensable to the permanent shelter which will have to bear the burden of heavy snows and the buffeting of icy winds. Fully alive to these perils, the spinner of the pine-tree considers himself bound, however importunate his hunger, not to saw through the rafters of his house.