IMPERFECT SOCIETIES OF INSECTS. 303 



his immediate followers succeed in the same line, the head of the second 

 touching the tail of the first : then comes an equal series of pairs, next of 

 threes, and so on as far as fifteen or twenty. The whole procession moves 

 regularly on with an even pace, each file treading upon the steps of those 

 that precede it. If the leader, arriving at a particular point, pursues a 

 different direction, all march to that point before they turn. Probably in 

 this they are guided by some scent imparted to the tracks by those that 

 pass over them. Sometimes the order of procession is different ; the 

 leader, who moves singly, is followed by two, these are succeeded by 

 three, then come four, and so on. When the leader, who in nothing 

 differs from the rest, and is probably the caterpillar nearest the entrance to 

 the nest, followed, as I have described, has proceeded to the distance of 

 about two feet, more or less, he makes a halt ; during which those which 

 remain come forth, take their places, the company forms into files, the 

 march is resumed, and all follow as regularly as if they kept time to music. 

 These larvae may be occasionally found at mid-day out of their nests, 

 packed close one to another without making any movement ; so that, 

 although they occupy a space sufficiently ample, it is not easy to discover 

 them. At other times, instead of being simply laid side by side, they are 

 formed into singular masses, in which they are heaped one upon another, 

 and, as it were, interwoven together. Thus, also, they are disposed in 

 their nests. Sometimes their families divide into two bands, which never 

 afterwards unite. 1 



The processionary caterpillars of the fir (those of Cnethocampa pityo- 

 campa), like the preceding, live in a common silken net placed at the extre- 

 mities of its branches, on which they feed ; and when they leave one tree 

 to proceed to another, they also move in procession, but with this striking 

 difference, that they all range themselves in a single file, the head of each 

 so exactly touching the tail of that before it as to form apparently one vast 

 caterpillar of from fifteen to twenty feet long, and thus traversing by a 

 continuous and occasionally slightly jerking motion, without ever breaking 

 their line, the path they have chosen. What is singular is, that if the first 

 caterpillar of the file be touched with the hand or a stick, it shrinks and is 

 visibly agitated, as if it feared to be stung by an Ichneumon, and the last of 

 the file, even if composed of six hundred, makes at the same instant, as 

 well as every intermediate individual, the same movements, as if struck by 

 an electric shock. 2 The individuals of another processionary caterpillar, 

 the perfect insect of which Mr. Ewing had not been able to rear, he informs 

 us march in circles, or rather ovals, and, when young, follow one another 

 round and round for hours together ! 3 



I have nothing further of importance to communicate to you on imper- 

 fect societies : in my next I shall begin the most interesting subject that 

 Entomology offers ; a subject, to say the least, including as great a portion 

 both of instruction and amusement as any branch of Natural History 

 affords ; I mean those perfect associations which have for their great 

 object the multiplication of the species, and the education, if such a term 

 may be here employed, of the young. This is too fertile a theme to be 

 confined to a single letter, but must occupy several. 



I am, &c. 



i Reaumur, ii. 180. 



De Villiers, Ann. Soc. Ent. de France, i. 201. 



3 Westwood in Trans. Ent. Soc. Lond. ii. proc. Iv. 



