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. [8] 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 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 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 [9] 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 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?