152 



LETTERS TO MR. WISE [CHAP. xvi. 



to have. The chief natural helpers against over-presence 

 of Caddis worms appear to be fish of various kinds, but the 

 increase of birds which naturally feed on fish herons, 

 &c., destroys the balance of nature, and Caddis worms 

 increase. 



[Miss Ormerod, quoting Mr. Coe in her Report for 1896, 

 says (p. 156) :- 



" When ever we find a bed of cresses attacked, we clear 

 away all the plants, drain off the water, and leave the bed 

 perfectly dry for two or three weeks in the autumn, previous 

 to the winter planting. If afterwards we find traces of the 



Water moth, magnified, and lines showing natural size (after 

 Westvvood) ; Caddis worm " cases " of Limnephilus ftavicornis, 

 magnified. 



FIG. 33. CADDIS WORMS, LARVAE OF CADDIS FLY OR WATER MOTH, 

 MO RM ONI A NIGROMA C ULA TA . 



worm, we wait until the plants are well established, then we 

 increase the volume of water and swim the bed, and pass 

 the backs of wooden rakes over the tops of the plants very 

 thoroughly. This process brings the bulk of the worms to 

 the surface, and they are let off down-stream with the 

 surplus water." 



To Dr. Fletcher she also wrote as follows: "Did I 



