30 STRUCTURE OF THE LEPIDOPTERA 



see it surrounded by a circle of little hooks, turning in all directions. 

 You will no longer wonder how it is that a caterpillar can hold so 

 tenaciously to a piece of twig that it is often almost impossible 

 to remove it without injury. 



Now put your caterpillar down, so that you may observe its gait. 

 If it happens to be one with the full complement of sixteen limbs, 

 you see that at each stride it makes but little progress. The 

 segments contract and relax alternately and in succession, thus 

 sending a series of wave-like motions along the body, and urging 

 onward the front segments while the claspers keep the hinder 

 portion firmly fixed. 



But if your caterpillar is one of the Geometers, with only two, 

 or perhaps three, pairs of claspers, the mode of procedure is very 

 different. The creature stretches its body out at full length, often 

 raising its head high in the air, and swing- 

 ing its long body right and left with a most 

 furious motion, as if to hastily scan the 

 neighbourhood. Then, having satisfied 

 itself as to the direction of its proposed 

 course (which, by the way, is often changed 

 considerably at almost every stride), it 

 holds on by the true legs and pulls its 

 hinder quarters forward till the body forms 

 almost a closed loop, with the fourth seg- 



FIG. 26.- ment near1 touchin the 



. . 



or A CATERPILLAR. claspers now become the holdfasts. The 

 little hooks with which they are provided 



are firmly fixed to the surface on which it is walking ; and the 

 body being again straightened out to its utmost length, the same 

 manoeuvre is repeated. So, you see, the insect progresses by 

 strides equal in length to about six segments of the body, and 

 these the longest segments generally ; and the rate at which the 

 strides succeed each other, especially in some of the smaller species, 

 is really astonishing. 



We have seen the caterpillar in the act of taking its walk, and 

 now we will give it a twig of its food plant so that we may see it 

 feed. It walks up the twig without hesitation for caterpillars 

 (excepting those which feed on roots) always seem to move upward 

 when in search of food and soon finds itself on a leaf. Over this 

 it walks till it reaches the edge ; and, grasping the edge firmly 

 between the claspers, so as to give perfectly free play to its legs and 



