338 IMPERFECT SOCIETIES OF INSECTS. 



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 impart- 

 ed 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 cater- 

 pillar 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. ^ 



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

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

 extremities 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 oS 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.^ — The individuals of another procession- 

 ary 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 1^ 



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, Stc. 



1 Reaumur, ii. 180. * De Villiers, Ann. Soc. Ent. de France, i. 201. 



2 Westwood in Trans. Ent. Soc. Land. ii. proc. Iv. 



