242 NATURAL HISTORY OF AQUATIC INSECTS CH. 



account of them in his " Gallery of Minerva." ] He 

 says that they feed upon leaves of celery, ranunculus, 

 and water-dock as well as upon other aquatic plants. 

 [Caddis-worms are usually vegetable feeders, but not 

 exclusively so. They devour larvae of Chironomus, 

 Ephemerae and other aquatic animals. Some are 

 altogether carnivorous, e.g. the Hydropsychidae. 

 When hungry, Caddis-worms devour one another. 

 They do not attack the end of the case, which can be 

 defended, but tear it open in the middle.] 



" Among these aquatic larvae there are many 

 species which I have not learnt to distinguish. The 

 commonest of all is much larger than the case-forming 

 larvae which I have just mentioned as living upon 

 land. 2 None of them are true caterpillars, but all 

 chancre to four-winged flies. We will consider the 



o o 



stages through which they pass, after we have ex- 

 amined their mode of life. 



" The body of these larvae is lodged in a silken 

 tube, to the outside of which are fastened fragments 

 of different substances, selected for the purpose of 

 strengthening and defending it. The sheaths may 

 be quite irregular, rough and prickly, or smooth and 

 symmetrical. When the old sheath becomes too 

 narrow or too short, the larva makes a fresh one. 3 

 Sometimes the new sheath differs more from the cast- 

 off one than our dress of to-day differs from that of our 



1 Works, folio edition, Vol. I. p. 37. 



2 Case-forming Lepidoptera. 



3 It is much more common for the larva to enlarge its case 

 by adding to the wider end, and cutting off the old and useless 

 part. 



