Food of the Ycllozvsfone Trout 485 



adult takes place. During this pupal period the "cornucopia" caddis- 

 worm (Leptocerus sp.) seeks the under side of rocks; there the 

 individuals cluster together, forming prickly patches which resemble 

 a cluster of dead spruce needles or the spines of a porcupine (figs. 

 128, 129). 



Still another species of the mountain waters builds itself a net- 

 work which it anchors with stones {Hydropsyche sp.). The net is 

 in the shape of a funnel, with a sieve across the wide end, and the 

 smaller end directed downstream. 



In the grub or larval stage the caddis-flies are particularly inter- 

 esting because of their manifold structures. They resemble cater- 

 pillars ; in fact, they are the nearest relatives of the moths and but- 

 terflies. They have tufts of iilaments on their bodies, a head and 

 six legs resembling those of caterpillars, and two posterior legs 

 provided with booklets which serve as grapples or claws to anchor 

 the worms in their cases. 



In the mountain streams none of the caddis-fly species are free 

 swimmers ; that is, their cases are all fixed. What migrating they 

 do, is done slowly and laboriously. In the lakes, ponds and quiet 

 streams one may find species with square or spiral cases swimming 

 about freely. 



After transformation the adult caddis-flies resemble tiny moths. 

 Indeed, they are often mistaken for moths, even by scientists, and 

 have been thus described. They like to gather on the rocks along 

 the shores of streams, where they run back and forth briskly, or fly 

 about the rapids, alighting on the water's surface and flying up into 

 the spray. They may even dive into the water, for the water does 

 not wet their wings and body. Only prolonged submergence will 

 water-log them. 



The Surface Food. — Besides these main items of the normal trout 

 diet in the mountain streams, the so-called "water bait," there is the 

 surface drift or surface bait of water-trapped animals, chiefly insects. 

 This comprises especially the weak fliers such as moths, ants and 

 grasshoppers, while spiders, centipeds, mice, and other animals may 

 occur. But the life of a trout stream is dependent on its normal 

 inhabitants, not on the odds and ends which a kind wind or accident 

 may provide. It is only during the brief summer period that surface 

 bait becomes important; and for a period of four to six weeks the 

 fish are largely dependent on this type of food for their existence. 

 That the emergence of their natural water bait, with the resulting 

 depletion of this primary food supply, should be synchronous with 

 the summer flights of ants, moths, grasshoppers and other poor 



5 



