ORDER TRICHOPTERA 171 



by these insects liave been found in rocks of the tertiary 

 period, so that it may be assumed that the aquatic case- 

 making habit had developed as far back as this period 

 in geological times. Aside from the fact that these may 

 furnish food for other aquatic organisms there is little 

 economic importance to be attached to them. The adults, 

 while occurring in abundance, do not feed upon any culti- 

 vated crops, and they rarely appear in such swarms as the 

 May flies, so that there is no especial annoyance from their 

 abundance. 



