264 HABITATIONS OF INSECTS. 



Not merely wool or hair, but another substance analogous to one em- 

 ployed in our dress, is adopted for their clothing by other insects. The 

 larva 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. 1 



The habitations which we have hitherto been considering are formed by 

 larvas that live on land : but others equally remarkable are constructed by 

 aquatic species, the larvas of the various Pliryganece L., a tribe of four- 

 winged insects, which an ordinary observer would call moths, but which are 

 even of a distinct order (Trichoptera), 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 larvae 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 leaves 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. 2 One, like the Sabell<e s , forms a horn-shaped 

 case composed of grains of sand, so equal in size, and so nicely and resu- 

 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. 4 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. 5 Some larvae constantly make their cases of the 

 same materials ; others employ indifferently any that are at hand ; and the 



* Reaum. iii. 130. 2 Ibid. 156159. 



3 Sowerby's Nat. Miscell Xo. ix. t. 51. 



4 De Geer, ii. 564. 6 Ibid. 



