I'ood of the Y ell ozvs tone Throat 48 r 



open Lamar River. Gardiner River, and the meadows of Slough 

 Creek, than in the gorges of the Lamar, Slough Creek, and the much- 

 shaded Lava Creek. 



Another factor possihly is the light W'hich may stimulate the species 

 to transform in early July. By this is meant both the light of the 

 shores and the light that penetrates the water. It has been noted 

 that in open, sunlit places transformation occurs earlier than in the 

 gloomy canyons. The amount of light to penetrate the water is 

 variable. The spring floods carry great quantities of sediment which 

 hinders the penetration of light. This makes the situation equally 

 difficult for fish and for the fisherman. For where the one cannot 

 see much in the line of prey in the water, the other cannot see the 

 fish, nor pick the likely places to cast. Perhaps this turbidity ac- 

 counts for the fact that when -the floods recede and the water grows 

 clearer the trout are hungry and " rise " more readily to bait ; for it 

 is obvious that the gloom resulting from the turbidity makes hunting 

 difficult for the fish, and at a time when he needs an excess of food 

 for the propagation of his kind. 



On the other hand, it has already been remarked that certain species 

 of stone-flies, such as the black and green stone-flies, do not emerge 

 until August, hence long after the floods have receded and the water 

 has clarified. Whichever the factor may be that chiefly stimulates 

 transformation, whether light or temperature, prolonged study and 

 experimentation are needed for its definite determination. 



From the examination of hundreds of stomachs of trout, especially 

 the cutthroat trout (Salmo clarkii) , it is evident that stone-flies, 

 both in their larval stage in the water and after transformation, form 

 about 90 per cent of the food of the trout. The foregoing merely 

 confirms what others have found as regards the dependence of fish 

 life in rapid streams on stone-flies for food. It is a curious fact 

 that some of the mountain streams which have a very low representa- 

 tion of stone-flies will not support fish life, or at least trout life. 



May-Hies. — The second and third groups, name'y the may-flies 

 and the caddis-flies, are variable in their representation and appear 

 to change their position of importance according to the stream. In 

 the Lamar River, for instance, the caddis-flies outnumber by far the 

 may-flies, while in the Yellowstone River, Lava Creek, and other 

 streams the may-flies are more conspicuous numerically. Whatever 

 the cause of this variability, they appear to be equally abundant in the 

 fish stomachs. 



May-flies are otherwise known as da3'-flies or shad-flies. They have 

 :heir names from the fact that they live but one day in the adult or 



