346 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
segments, each bearing a pair of 5-jointed legs. The first segment, or 
pr ‘othorax, bears two spiracles, one on each side, and on the top sur- 
face a sclerite, known as the cervical, or thoracic, shield. The abdomen 
is composed of 10 segments, each of ‘the first 8 bearing a pair of spira- 
cles. There may be from 2 to 5 pairs of abdominal legs or prolegs, 
which are fleshy, without joints, and are cast off with the last larval 
skin. On forms that feed externally prolegs are never present on the 
first or second abdominal segments. This distinguishes them from 
sawfly larvae, which have prolegs on the second abdominal segment. 
The larva may appear as naked; sparsely or densely clothed with 
hairs, bristles, or spines; or equipped with fleshy or horny warts and 
tubercles. The fact is, however, that the body bears a regular arrange- 
ment of setae on each segment, which are of great value in identifying 
the different species. 
From time to time as the larva increases in size, its outer skin, or 
epidermis, becomes too tight to admit further growth, so a new and 
more flexible skin is formed underneath the old one, and the old skin 
then splits back of the head along the dorsal line and is molted, or 
shed. The number of molts ranges from 3 to 10 in the different species. 
Prior to the first molt the darva is said to be a first instar, between the 
first and second molt, a second instar, and so on until it becomes full- 
Brown. PUPAE 
When the larvae are full grown they cease to feed, usually seek a 
sheltered place, and then void the contents of their ‘digestive tract. 
Most species pupate within cocoons constructed by the larvae. A 
cocoon may be composed entirely of silk, of a folded leaf or several 
leaves drawn together with silk, a mixture of silk and hairs from the 
body of the larva, particles of wood or other substances, a combination 
of silk and fluid secretion, which dries and forms a hard-shelled cocoon, 
or an earthen cell made from particles of soil cemented together. A 
few species have naked pupae, usually protectively colored, which 
are attached by the caudal extremity to some object by silk and often 
with a silken girdle to hold them in place. Cocoons may be formed on 
any part of a tree, in the soll, or in any conceivable place that offers 
protection. The pupae, or “chr ysalids,” of some species of the butter- 
flies are ornamented with gold- or silver-colored spots. 
Preparatory to pupation, the larva decreases in length but increases 
in girth, and finally the action and pressure from within causes the 
skin to split along the dorsal line of the thorax, and the freshly formed 
pupa forces itself out. Considerable transformation from the larval 
stage has taken place. The divisions of the head, thorax, and abdomen 
are easily recognized, and the appendages characteristic of the adult, 
closely bound to the body, are plainly marked on the pupa. Many 
of the internal organs undergo extensive changes during the pupal 
period. 
The method of escape by the adult from the pupa and cocoon varies 
greatly with the different species. Immediately prior to the emer- 
gence of the adult, some pupae develop a considerable power of motion 
by the use of hooks or other processes and the freeing of some of the 
segments and appendages. In many species before the adult emerges 
the pupa is thus able to work its way out of the cocoon, and to the 
surface of the ground or to the entrance of the larval gallery. Many 
species use a process on the posterior end of the pupa, known as the 
