caterpillars of the Clearwing Moths (Sesiidae) burrow through the wood
of trees, eating the timber as they go. The little irritable
caterpillars of the Bell Moths (Tortricidae) roll leaves, fastening the
edges together with silk, and thus make for themselves a shelter; or
they bore their way into seeds or fruits, like the larva of the Codling
Moth that is the cause of 'worm-eaten' apples, too well-known to
orchard-keepers. Very many small caterpillars mine between the two skins
of a leaf, eating out the soft green tissue, and giving rise to a
characteristic blister in form of a spreading patch or a narrow sinuous
track through the leaf. The caterpillars of the Clothes-moths (Tineidae)
make for themselves garments out of their own excrement, the particles
fastened together by silk. In such curious cylindrical cases they wander
over the wool or fur, feeding and indirectly supplying themselves with
clothing at the same time.

The case-forming habit of the Clothes-moth caterpillars leads us
naturally to consider the similar habit adopted by their allies the
Caddis-larvae which live in the waters of ponds and streams, for the
Caddis-flies (Trichoptera) have much in common with the more primitive
Lepidoptera. The caddis-larva is as a rule of the eruciform type, but
with well-developed thoracic legs, and with hook-like tail-appendages;
by means of the latter it anchors itself to the extremity of its curious
'house.' It is of interest to note that in the earlier stages of some
caddises lately described and figured by A.J. Siltala (1907), the legs
are relatively very long, and the larva is quite campodeiform in aspect.
Some of these caddis-grubs retain the campodeiform condition and do not
shelter permanently in cases, as their relations do. Different genera of
caddises differ in their mode of building. Some fasten together
fragments of water-weeds and plant refuse, others take tiny particles of
stone, of which they make firmly compacted walls, others again lay hold