198 INSECT ARTIZANS AND THEIR WORK 



the materials he considers most suitable for the 

 circumstances of his life. One species {Limnofhilus 

 fellucidus) is content with bits of leaves which 

 enable him to pass unnoticed among the waterweeds 

 from which they were bitten. Limnofhilus rhom- 

 hicus takes short pieces of grass-stem or bits of 

 horsetail and arranges them transversely to the 

 length of the case, so that the finished effect reminds 

 one of a hedgehog. Z. flavicornis is not so exclusive 

 in its choice of material ; it will make its case of 

 bits of thin twig not very orderly in their arrange- 

 ment, or it will capture small water-snails, chiefly 

 species of Planorbis, but often the little freshwater 

 bivalves {Spht^rium), in either case with the shell 

 still tenanted by its builder. Such a dress of 

 living molluscs is apparently cumbrous by reason of 

 its weight, so we often find that the tailor has 

 redressed the balance by fixing along each side of 

 his tube a bit of stick perhaps twice its length. 

 This gives the required buoyancy, though not 

 sufficient to float the structure. Aiiaholia nervosa, 

 which makes its case of small fragments of stone, 

 adopts the same method for lightening it. Seri- 

 costoma and Setodes make their cases of sand, very 

 neatly spread over the silk lining, slightly tapering 

 and curved. Setodes is in form exactly like the 

 marine shell known as the tusk shell {Dentalium). 



These cases, carefully examined, will be found 

 to be broader at one end than at the other — " and 

 thereby hangs a tale." The Caddis Worm, as the 

 advance of life causes it to increase both in girth 



