188 
THE STUDY OF INSECTS. 
make this style of house live in still water, and may, there¬ 
fore, be easily kept alive in aquaria. 
There are caddice-worm houses closely resembling in plan 
those just described but differing in appearance, being made 
of bits of moss. Sometimes the houses are built of leaves ; 
these may be fastened so as to form a flat case; or are ar¬ 
ranged in three planes, so as to form a tube, a cross-section 
of which is a triangle. 
Other Caddice-worms are masons, building their houses of 
grains of sand or of small stones. Sometimes these houses 
are tubes very regular in outline, being composed only of 
grains of sand fastened together with silk; but certain spe¬ 
cies of Mason Caddice-worms fasten larger stones on each side 
of this tube of sand (Fig. 228). Some of the species that 
Fig. 228. 
Fig. 229. 
build tubes of sand make spiral houses which very closely 
resemble in form snail-shells (Fig. 229). 
Whether stones or wood are used to build these houses 
the material is always fastened together by silk, which the 
larvae spin from the mouth in the same manner as do cater- 
pillars. In some species the case is 
composed entirely of silk. Figure 230 
represents the form of such a case, which 
Fig. 230, . . - , . 
is common in some of our lakes. 
Among the simplest of the various forms of houses built 
by Caddice-worms are those made by certain species that live 
under stones in rapid streams. These consist merely of a 
few pebbles fastened to the lower surface of a larger stone 
by threads of silk. In the space between these pebbles the 
worm more or less perfect tube of silk, within which 
