The Life of the Caterpillar

by Jean-Henri Fabre

Twice renewed with the same results, this test proves that the Pine Caterpillars are not alive to the danger of their split dwelling. [[41]]Expert spinners though they be, they seem as unconscious of the ruin of their work as the spools in a factory are of a broken thread. They could easily make good the damage by stopping up the breach with the silk that is lavished elsewhere without urgent need; they could weave upon it a material as thick and solid as the rest of the walls. But no, they placidly continue their habitual task; they spin as they spun yesterday and as they will spin to-morrow, strengthening the parts that are already strong, thickening what is already thick enough; and not one thinks of stopping the disastrous gap. To let a piece into that hole would mean weaving the tent all over again from the beginning; and no insect, however industrious, goes back to what it has already done.

I have often called attention to this feature in animal psychology; notably I have described the ineptitude of the caterpillar of the Great Peacock Moth.[1] When the experimenter lops the top off the complicated eel-trap which forms the pointed end of the cocoon, this caterpillar spends the silk remaining [[42]]to him in work of secondary importance, instead of making good the series of cones, each fitting into the other, which are so essential to the hermit’s protection. He continues his normal task imperturbably, as though nothing out of the way had taken place. Even so does the spinner in the pine-tree act with his burst tent.

Your foster-parent must perpetrate yet another piece of mischief, O my Processionary; but this time it shall be to your advantage! It does not take me long to perceive that the nests intended to last through the winter often contain a population much greater than that of the temporary shelters woven by the very young caterpillars. I also notice that, when they have attained their ultimate dimensions, these nests differ very considerably in size. The largest of them are equal to five or six of the smallest. What is the cause of these variations?

Certainly, if all the eggs turned out well, the scaly cylinder containing the laying of a single mother would be enough to fill a splendid purse: there are three hundred enamelled beads here for hatching. But in families which swarm unduly an enormous waste always [[43]]takes places and restores the balance of things; if the called are legion, the chosen are a well thinned-out troop, as is proved by the Cicada, the Praying Mantis[2] and the Cricket.

The Pine Processionary, another crucible of organic matter of which various devourers take advantage, is also reduced in numbers immediately after the hatching. The delicate mouthful has shrunk to a few dozens of survivors around the light globular network in which the family passes the sunny autumn days. Soon they will have to be thinking of the stoutly-built winter tent. At such a time, it would be a boon if they could be many, for from union springs strength.

I suspect an easy method of fusion among a few families. To serve them as a guide in their peregrinations about the tree, the caterpillars have their silk ribbon, which they follow on their return, after describing a bend. They may also miss it and strike another, one differing in no respect from their own. This new ribbon marks the way to some nest situated in the neighbourhood. The strayed [[44]]caterpillars, failing to distinguish it from their own ribbon, follow it conscientiously and in this manner end by reaching a strange dwelling. Suppose them to be peacefully received: what will happen?

Once fused, the several groups assembled by the accident of the path will form a powerful city, fitted to produce great works; the concerted weaklings will give rise to a strong, united body. This would explain the thickly-populated, bulky nests situated so near to others that have remained puny. The former would be the work of a syndicate incorporating the interests of spinners collected from different parts; the latter would belong to families left in isolation by the luck of the road.

It remains to be seen whether the chance-comers, guided by a strange ribbon, meet with a good reception in the new abode. The experiment is easily made upon the nests in the greenhouse. In the evening, at the hours devoted to grazing, I remove with a pruning-shears the different little branches covered with the population of one nest and lay them on the provisions of the neighbouring nest, which provisions are also overrun with caterpillars. [[45]]Or I can make shorter work of it by taking the whole bunch, well covered with the troop, of the first pouch and planting it right beside the bunch of the second, so that the leaves of the two mingle a little at the edges.

There is not the least quarrelling between the real proprietors and the new arrivals. Both go on peacefully browsing, as though nothing had happened. And all without hesitation, when bed-time comes, make for the nest, like brothers who have always lived together; all do some spinning before retiring to rest, thicken the blanket a little and are then swallowed up in the dormitory. By repeating the same operation next day and, if necessary, the day after, in order to collect the laggards, I succeed without the slightest difficulty in wholly depopulating the first nest and transferring all its caterpillars to the second.

I venture to do something better still. The same method of transportation allows me to quadruple the output of a spinning-mill by adding to it the workers of three similar establishments. And, if I limit myself to this increase, the reason is not that any confusion [[46]]manifests itself in this shifting of quarters, but that I see no bounds to my experiment, so cheerfully do the caterpillars accept any addition to their number. The more spinners, the more spinning: a very judicious rule of conduct.