THE APPEARANCE OF FLIES, ETC. 173 



face, where they can detect the flies in spite of the 

 absence of movement. 



The pupae of insects rising to the surface of the 

 water at the time of metamorphosis are sometimes 

 fed upon by trout before they reach the surface. 

 The principle of movement must play a large part 

 in betrayal here. 



Insects that have undergone complete meta- 

 morphosis are regularly fed upon by trout under 

 the surface. Besides shape and movement, colour 

 comes into play here. A sunk, wet, artificial fly 

 is often much more killing than a floating fly. The 

 sight, and judgment of distance, of trout, is probably 

 better in regard to objects under the water, than 

 motionless ones standing on the surface film. 



Wet fly fishermen will probably generally agree 

 that a yellow-bodied artificial fly accounts for many 

 of their best baskets. This colour of body is well 

 adapted to catch glints of light. In this connection, 

 it is interesting to consider the nymph of the Stone- 

 fly (Perla), known to anglers as the creeper. The 

 sight of man is generally acknowledged to be quite 

 as good as that of trout, yet it is extremely difficult 

 for him to see a creeper on the bottom of a stream, 

 so perfect is the protective colouring of its back. 

 As soon, however, as it is disturbed and loses its 

 feet, the glint of its yellow body betrays it. 



