486 
LEPlbOPTEkA. 
nature of the support, but the inner layer is often formed of practically 
one thread, disposed regularly round and round and finally ending at 
some point inside the cocoon where the caterpillar finishes. The cocoon 
is thus built up from inside, the outside layer first, the fine inner layer 
last. In many insects this is then cemented with material produced 
by the caterpillar from the alimentary canal and the cocoon is finished. 
In some, the production of silk is not continuous, the caterpillar probably 
resting, and the cocoon consists of distinct layers which may be separated ; 
this is the case, for instance, in Eri and is the reason why a distinct thread 
cannot be got from these cocoons. 
This is the principal use of silk in the insect world, for the prepara¬ 
tion of the cocoon to shelter the pupa ; the cocoon may not be of pure 
silk but may include fragments of plants, leaves, etc., or as well as earth 
or other matter ; the hair of the larva is in many used with the silk and 
forms a large part of the cocoon. Silk is also produced by glands opening 
on other parts of the body than the lower lip and then differs little from 
the gummy matter produced, for instance, by some weevils for the prepar¬ 
ation of the cocoon (c. /. Cionus, Curculionidce). 
Silk is not known to be produced by any member of the order 
Orthoptera. The Embiidce produce very delicate silk from glands situate 
in the forefeet; with this they prepare small web-like shelters on the soil 
under which they live. The Psocidce prepare somewhat similar webs on the 
bark of trees or on old wood, the silk being excreted from the mouth- 
parts in the usual way and being of a very fine nature. The Myrmeleonides 
and Hemerobiides among the Hemerobiidce produce silk cocoons ; in the 
former the silk is the product of anal glands and issues from a single spin¬ 
neret at the apex of the abdomen; the cocoon is white and hard, the pupa 
being provided with jaws for cutting through and emerging. In the 
Hemerobiides the cocoon is round and white or is very flimsy and partly 
formed of a leaf. 
Among the Phryganeidce silk is in constant use for the preparation 
of the cases in which the larva lives and is the product of the salivary 
glands ; some species ( Hydropsyche) use the silk also in the preparation 
of the nets which are used to catch their prey. The use and production of 
silk in this group is similar to that in Lepidoptera. Throughout the 
Hymenoptera silk is produced by the larva for the cocoon ; these cocoons 
are of very varied form, but are almost universally formed of very close 
fine silk. No cocoon is formed by some of the parasitic forms which 
pupate in the skin of the host. Among Formicidce the silk is sometimes 
employed for nest building ; this is especially the case with the 
common red tree Ant ( (Eecophylla smaragdina) an account of which is 
given on page 232. 
Among Coleoptera true silk is not formed, cocoons being made of 
cement produced by the alimentary canal; in at least one species of Chrys- 
omelid, however ( Oides bipunctatus) , this secretion takes the form of 
coarse threads spun over the pupa and forming a very rough cocoon of 
