How to obtain it. 213 



as it is one that is well known to all observers, and that is the 

 little whirlygig beetle (Gyrinus natator], so called because it 

 swims round and whirls about on the surface of the water. It is 

 rather curious in structure, an excellent swimmer, and provided 

 with top and bottom eyes, so to speak, so that it can see either a 

 bird above or a fish below, if they approach with hostile intentions. 

 It also emits an oily fluid if attacked, and has a very disagreeable 

 smell. Its food, so far as we have observed, appears to be flies 

 and gnats just emerging from their larvae on the surface of the 

 water ; at all events it pounces on these with avidity. 



We may now consider a few of the flies that spend their 

 larval period in water. They form in most cases a very consider- 

 able portion of the natural supply of fish food. Two of the chief 

 families of such flies are the caddis flies, or Trichopiera, and the 

 Neuroptera, or nerve-winged flies. There are some two hundred 

 varieties of caddis flies, or "water moths," as they are sometimes 

 called, one of the largest and most typical being the Phryganea 



Fig. 30. Caddis Fly, Phryganea grandis. 



grandis of the entomologists, or the " brown owl " of the angler 

 so called because of its brown russet colour and soft downy wings. 

 The caddis flies lay a considerable number of eggs, sometimes in 

 the water on equatic plants, and at other times on marginal plants,, 

 whence the young larvae, on hatching, have to find their way into- 

 the water as best they may, many doubtless perishing en route^ 

 Once in the water the larvae clothe themselves with bits of stick, 

 stone, rush, leaf, sand, shells, or anything else they come across, 

 forming a tube which serves the double purpose of a protection 

 from their enemies, and also an ambush in which they can 

 approach their prey unobserved. Their food consists chiefly 

 of animal matter, dead or alive ; they are capital scavengers, and 

 are excellent trout food, but the larger varieties are great enemies 

 to the young fish, and they are provided with a pair of most 



