INTRODUCTION. XXIX 



Caterpillars are very voracious, and increase in size very 

 rapidly ; but as their skin does not expand in proportion, it 

 soon becomes too tight. Then the caterpillar moults, casting 

 off not only the skin, but the horny covering of the head and 

 jaws, and even the lining of the principal internal organs. 

 When a caterpillar is about to moult, its colour begins to fade, 

 and it ceases to eat, and grows sluggish ; and after the moult 

 is over it remains sluggish for a short time, before beginning 

 to eat with renewed voracity. Many caterpillars do not alter 

 very much in appearance or habits or structure from moult to 

 moult ; but some differ considerably. Thus, the young cater- 

 pillars which will have the usual complement of sixteen legs 

 when full grown, sometimes have only ten when they first leave 

 the egg ; and others change their colour, or acquire additional 

 spines, &c., in the course of successive moults. As regards 

 habits, several species of caterpillars live in colonies when they 

 are young, and sometimes under a web ; but when they grow 

 older they separate, and scatter themselves over the plants on 

 which they feed. The caterpillars of some of the smaller 

 Moths are " miners," living in mines or galleries in the sub- 

 stance of leaves ; and the caterpillars of the Green Forester 

 Moths have a similar habit when young, but when older feed 

 exposed on their food-plants. Many caterpillars are protected 

 by their close resemblance to the plants on which they feed, 

 and the brown caterpillars of some of the Geometrid, or 

 Loopers, as they are termed, fix themselves on a branch with 

 their hind-legs, and then stretch their bodies stifHy out, in 

 which attitude they are not to be distinguished from bits of dry 

 stick. Bates once met with a caterpillar, during his travels on 

 the Amazons, which startled him from its exact resemblance to 

 a small venomous snake. Some few brightly-coloured cater- 

 pillars, such as those of the Spurge Hawk Moth, feed in very 

 exposed situations ; but in such cases their bright colours pro- 



