LEPIDOPTERA. 
79 
the mischief has been done. So voracious are larvae 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. off the edges of leaves, or gnawing amongst decaying timber; a pair 
of small, short antennae 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 larv®, 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, antennas, 
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 pup® 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 
