March, I9I3.] SleIGHT : TrICHOPTERA. 5 



with but very few exceptions, they are confined to fresh water and 

 are rarely, if ever, to be found in any but permanent fresh water 

 bodies. 



The larvae of Trichoptera have the extremely interesting habit of 

 protecting themselves by building some sort of a case in which to live. 

 Their cases are of a great variety of form and structure, as will be 

 pointed out later. Those larvse which live in very swift streams usu- 

 ally fasten their cases to stones by means of silken threads. In the 

 more quiet waters the larvae crawl from place to place, dragging their 

 cases with them. Pupation takes place in the larval case. When 

 it is time for the adult to emerge, the pupae come to the surface 

 either by crawling or by swimming with their middle pair of legs. 

 The middle legs of the pupae possess hairs adapting them to this use. 



It is very interesting to watch some of the Hydropsychids, which 

 live in swift streams emerge. As soon as the pupa reaches the sur- 

 face its skin splits down the back and the adult flies away, leaving 

 the skin on the surface of the water. It is almost as though the 

 pupa swam to the surface and immediately flew. For the most part 

 the pupae of those species which live in ponds and slow flowing 

 streams, crawl to the surface or beyond and the adult takes some 

 time to dry its wings before flying. 



With the possible exception of the Hydropsychidae, the larvae seem 

 to be vegetarians, many of them feeding on the slime and decaying 

 leaves found on the bottom. Even some of these will not refuse 

 pieces of meat and it is believed that the net-building Hydropsyche at 

 least are almost entirely carnivorous. The adults have rudimentary 

 mouthparts and as far as is known they do not feed. 



Usually both larvae and pupae breathe by means of tracheal gills. 

 Some, however, lack gills and breathe through the skin. In my opin- 

 ion there is little relation between distribution and the amount of 

 oxygen in the water, as is indicated by the following experiments: 



It has been pointed out that swift streams tend to be well sup- 

 plied with oxygen and there is a general feeling that animals from 

 such environment are difficult to rear in ordinary aquaria. However, 

 I have kept even a net-building Hydropsyche for a week or more in 

 mason jars. 



In June last I also transferred about 50 of the snail-shell-like 

 cases (Helicopsyche annulicornis Banks) from swift water to a 



