48 POND LIFE 



leaves into long, narrow pieces and entwine these spirally in 

 a similar manner to a puttie. 



Some tusk-shaped cases are made of most minute grains of 

 sand. So carefully are these tiny grains of silica chosen, and so 

 accurately are they fastened together, that it is hard to believe 

 the mosaic can be the work of an insect. Some larvae prefer 

 well-soaked, partly-decayed leaves, and arrange them so as to 

 produce a huge structure of flattened appearance. In fact 

 caddis-worms, depending on the species, use practically every- 

 thing of suitable specific gravity. Cases composed entirely of 

 seeds, sticks, leaves, stones, stems of plants are frequently 

 found. In fact, as the reader will notice, each species of caddis- 

 worm has its particular dress, which does not depend entirely 

 on its surroundings. That is to say, one species prefers to use 

 the shells of Planorbis the flat-shelled mollusc so common in 

 ditches and will never, if possible, use anything else ; yet 

 should these molluscs be absent, the larva of Limnophilus 

 flavicornis does not give up in despair, and having made a 

 thorough but uusuccessful search for what it requires, sets to 

 and builds a case of the most suitable material it is able to 

 find. It then seems to lose all idea of making use of any one 

 material in particular, but chooses the most suitable that it 

 comes across sticks, stones, leaves, and even barley and wheat 

 grains. 



The building of the case is by no means plain sailing, even 

 should the desired material be in abundance. For each little 

 larva has to reckon with ninety or more brothers and sisters, not 

 including distant relations and perfect strangers, who are 

 equally keen on making a home in the shortest possible time. 

 And so, no sooner has one caddis-worm deftly chosen a suitable 

 object for its personal decoration and started weaving it to 

 the others of its choice, than it is rudely interrupted by a 

 relation or acquaintance. 



Caddis-worms engaged in building fight continually, in a 

 very similar manner as a large number of dogs would over 

 a meagre supply of bones. The owner of a case just started 

 is seized, and during the subsequent struggle loses the result 

 of its labour the various parts being instantly utilised by its 

 friends and relations ; so one can imagine that the completion 

 of a case is no easy matter should the necessary material be 

 scarce. 



The reader may wonder how, considering this excitement 

 and trouble, it is possible to build a case resembling mosaic. 

 It happens that there is usually no scarcity of sand in most 

 places, and so those using this material can each build their 



