The Pine Processionary seems to belong to this number. In his second costume, when the segments bear on their dorsal faces an elegant red mosaic, he differs apparently from other caterpillars only by a more delicate general impressionability, unless this mosaic be endowed with aptitudes unknown elsewhere. If the nocturnal spinner is still none too generously equipped, it must be remembered that the season which he passes in this condition is nearly always clement. The really formidable nights hardly set in before January. But then, as a safeguard in his peregrinations, the Pine Processionary cleaves his back with a series of mouths which yawn open to sample the air from time to time and to give a warning of the sudden storm. Until further evidence is forthcoming, therefore, the dorsal slits are, to my mind, meteorological instruments, barometers influenced by the main fluctuations of the atmosphere. To go beyond suspicions, though these are well based, is for me impossible. I lack the equipment necessary to delve more deeply into the subject. But I have given a hint. It is for those who are better favoured in the matter of resources to find the final solution of this interesting problem. CHAPTER V THE PINE PROCESSIONARY: THE MOTH When March comes, the caterpillars reared in domesticity never cease processioning. Many leave the greenhouse, which remains open; they go in search of a suitable spot for the approaching metamorphosis. This is the final exodus, the definite abandonment of the nest and the pine-tree. The pilgrims are much faded, whitish, with a few russet hairs on their backs. On the 20th of March I spend a whole morning watching the evolutions of a file some three yards in length, containing about a hundred emigrants. The procession toils grimly along, undulating over the dusty ground, where it leaves a furrow. Then it breaks into a small number of groups, which crowd together and remain quiescent save for sudden oscillations of the hind-quarters. After a halt of varying duration, these groups resume their march, henceforward forming independent processions. They take no settled direction. This one goes forward, that one goes back; one turns to the left and another to the right. There is no rule about their marching, no positive goal. One procession, after describing a loop, retraces its steps. Yet there is a general tendency towards that wall of the greenhouse which faces the south and reflects the sun’s rays with added fervour. The sole guide, it would seem, is the amount of sun which a place obtains; the directions whence the greatest heat comes are preferred.