264 HABITATIONS OF INSECTS. 
Not merely wool or hair, but another substance analogous to one em- 
loyed in our dress, is adopted for their clothing by other insects. The 
arva of a fly which lives on the seeds of willows makes itself a very 
beautiful case of their cottony down, not only impervious to wet and cold, 
but serving, if accidentally blown into the water, which, from the situation 
of these trees, frequently happens, as a buoyant little barge which is wafted 
safely to the shore. 
The habitations which we have hitherto been considering are formed by 
larvae that live on /and: but others equally remarkable are constructed by 
aquatic species, the larve of the various Phryganee L., a tribe of fours 
winged insects, which an ordinary observer would call moths, but which are 
_ even of a distinct order (Z'vrichoptera), not having their wings covered by 
the scales which adorn the lepidopterous race. If you are desirous of 
examining the insects to which I am alluding, you have only to place 
yourself by the side of a clear and shallow pool of water, and you cannot 
fail to observe at the bottom little oblong moving masses, resembling pieces 
of straw, wood, or even stone. These are the larve in question, well 
known to fishermen by the title of Caddis-worms, and which, if you take 
them out of the water, you will observe to inhabit cases of a very singu- 
lar conformation. Of the larva itself, which somewhat resembles the cater- 
pillars of many Lepidoptera, nothing is to be seen but the head and six legs, 
by means of which it moves itself in the water, and drags after it the case 
in which the rest of the body is inclosed, and into which on any alarm it 
wholly retires, The construction of these habitations is very various, 
Some select four or five pieces of the leaves of grass, which they glue to- 
gether into a shapely polygonal case; others employ portions of the stems 
of rushes, placed side by side, so as to form an elegant fluted cylinder ; some 
arrange round them pieces of leayes like a spirally-rolled ribbon ; others 
inclose themselves in a mass of the leaves of any aquatic plants united 
without regularity ; and others again form their abode of minute pieces of 
wood, either fresh or decayed.® One, like the Sabelle’, forms a horn-shaped 
case composed of grains of sand, so equal in size, and so nicely and regu- 
larly gummed together, the sides throughout being of the thickness of one 
grain only, that the first time I viewed it I could scarcely persuade myself 
it could be the work of an insect. The case of Leptocerus bimaculatus, 
which is less artificially constructed of a mixture of mud and sand, is pyri- 
form, and has its end curiously stopped by a plate formed of grains of sand, 
with a central aperture.t Other species construct houses which may be 
called alive, forming them of the shells of various aquatic snails of different 
kinds and sizes, even while inhabited, all of which are immoveably fixed to 
it, and dragged about at its pleasure—a covering as singular as if a savage, 
instead of clothing himself with squirrels’ skins, should sew together into a 
coat the animals themselves. However various may be the form of the 
case externally, within it is usually cylindrical, and lined with silk; and 
though seldom apparently wider than just to admit the body of the insect, 
some species have the power of turning round in it, and of putting out 
their head at either end.> Some laryze constantly make their cases of the 
same materials ; others employ indifferently any that are at hand ; and the 
1 Reaum. iii. 130. 2 Thid, 1566-159, 
5 Sowerby’s Wat. Miscell. No. ix. t. 51. 
4 De Geer, ii. 564, 5 Ibid. 
