270 



NATURAL HISTORY. 



[CH. XVI 



number of caterpillars, its dimensions must of course 

 be considerable. Some of them measure eighteen 

 or twenty inches in length, five or six in breadth, 

 and four in depth. Each is a simple pocket without 

 partitions; the sides being composed of several 

 layers of a grayish coloured silk, which assimilates 

 so well with the natural hue of the oak, as com- 

 pletely to deceive the eyes. 



When the glow of day begins to soften, and the 

 sun is about to set, these insects quit their habita- 

 tion in order to proceed in search of food the twi- 

 light and the night constituting the period of their 

 activity. Their movements are conducted with 

 wonderful regularity. A single caterpillar first goes 

 out of the nest, and is immediately followed by 

 others which form a sort of procession : the leader 

 is succeeded by two moving abreast ; that rank by 

 a third, composed of three abreast ; and so on till 

 sometimes the last row contains twenty ranged side 

 by side ; the ranks are so compact, that the tail of 

 one row is touched by the heads of those which suc- 

 ceed ; and in each row the caterpillars also touch 

 throughout the whole length of the body. They 



