CATERPILLARS. 
259 
to the air. Some caterpillars make but very little silk ; 
others, such as the silk-worm and the apple-tree caterpillar, 
produce it in great abundance. 
Some caterpillars herd together in great numbers, and 
pass the early period of their existence in society; and of 
these there are species which unite in their labors, and con- 
struct tents serving as a common habitation in which they 
live, or to which they retire occasionally for shelter. Others 
pass their lives in solitude, either exposed to the light and 
air, or sheltered in leaves folded over their bodies, or form 
for themselves silken sheaths, which are either fixed or 
portable. Some make their abodes in the stems of plants, 
or mine in the pulpy substance of leaves ; and others con- 
ceal themselves in the ground, from which they issue only 
when in search of food. 
Caterpillars usually change their skins about four times 
before they come to their growth. At length they leave off 
eating entirely, and prepare for their first transformation. 
Most of them, at this period, spin around their bodies a sort 
of shroud or cocoon, into which some interweave the hairs 
of their own bodies, and some employ, in the same wav, 
leaves, bits of wood, or even grains of earth. Other cater- 
pillars suspend themselves, in various ways, by silken threads, 
without enclosing their bodies in cocoons ; and again, there 
are others which merely enter the earth to undergo their 
transformations. 
When the caterpillar has thus prepared itself for the ap- 
proaching change, by repeated exertions and struggles it 
hursts open the skin on the top of its back, withdraws the 
fore part of its body, and works the skin backwards till the 
hinder extremity is extricated. It then no longer appears 
in the caterpillar form, but has become a pupa or chrysalis, 
shorter than the caterpillar, and at first sight apparently 
without a head or limbs. On close examination, however, 
there may be found traces of a head, tongue, antennae, wings, 
ancj legs, closely pressed to the body, to which these parts 
