LEPIDOPTERA. 79 



the mischief has been done. So voracious are larvse that huge oak forests may be 

 in a few days swept bare of almost every vestige of foliage. 



structure of The body consists of a head bearing biting mandibles for nipping 



Larva. o ff the edges of leaves, or gnawing amongst decaying timber ; a pair 

 of small, short antennas form appendages on either side ; and just behind three 

 simple eyes, or ocelli, on either side, very different from the large compound eyes 

 of the perfect insect. Behind the head lie eleven segments or movable rings. 

 Three of these, close behind the head, correspond to the thorax of the adult, 

 and bear the three pairs of thoracic legs, short and horny, exactly corresponding to 

 the three pair of legs of the butterfly or moth. The other segments bear the pro- 

 legs, or claspers varying in number from one to five pairs used for clinging to 

 leaves and other surfaces. In some of the moths the last pair are obsolete as legs, 

 and are developed into a pair of horns, supposed to be for protective purposes, as 

 for instance in the puss-moth. A caterpillar may thus possess sixteen legs, though 

 often there is not the full number. 



A very curious form of larva is that producing the insects known as the 

 geometers, so called because of the peculiar gait of the caterpillar, which measures 

 out the surface over which it passes with a regular series of equal strides or loops. 

 Their body is long, but since there are but four pro-legs, they cannot crawl, but by 

 bringing up the hinder-legs advancing the head, and again bringing forward the 

 tail, the caterpillar spans the space to be traversed by a series of looping strides. 

 Hence the Americans call them " span-worms." These larvae, too, are remarkable 

 for their resemblance when the head is stretched outwards to a broken twig, a 

 likeness which undoubtedly secures them from many dangerous foes. Many larvae 

 are protected by their similarity in colour to the surrounding foliage, and it 

 has been supposed that the pigment from the leaves which the caterpillar eats 

 lends its characteristic hue to its devourer. From the moment of hatching until 

 the final moult, when the caterpillar enters the pupa state, it undergoes a series of 

 from eight to ten changes of the skin. These changes form crises in the lives of 

 larvae, which, at any rate in captivity, sometimes die during the process. 



The stage immediately preceding that of the perfect form is 

 usually called, when reference is made to the butterflies, the chrysalis 

 state ; but in the case of the moths, the pupa state, though there is no essential differ- 

 ence between the two. In this strange quiescent state the wings, legs, antennae, 

 and proboscis of the future insect can be seen fully formed and folded tightly 

 within the outer covering. The only signs of vitality are given by wriggling 

 movements of the segmented abdomen, when the pupa is irritated. The hard 

 external covering is useful for resisting the attacks of predaceous insects, though 

 of course not securing them immunity from mice, birds, or moles, which devour 

 them with avidity. The chrysalis of a butterfly is usually angular and gilded. 

 Some are suspended simply by the tail, others have a silken girdle round the 

 middle to keep them fast, while some spin a very slight cocoon. The pupae of the 

 moths, on the other hand, are dull red, usually smooth mummy-like objects, to 

 which likeness the word pupa or " puppet " doubtless refers. The greater part of 

 these lie simply in the earth, beneath moss or bark, wherever the larva has crawled 

 to effect the change, without any additional covering. Others form a hard cocoon 



