336 THE RIVER-SIDE NATURALIST. 



and the case exposed to light and sun. In forty-eight hours 

 they began to change as described above. When emerged 

 from the sub- imago to the imago state the abdomen was of 

 a light yellow, the segments lighter still. After some hours 

 the colour darkened, and on the 24th, i.e., in three days, they 

 had all become a dark-reddish, claret-colour, the males a 

 deeper colour than the females. These insects lived eleven 

 days ; so that an insect caught immediately after it had 

 assumed its imago state might easily be described as a 

 species different to the same insect caught two or three 

 days after. 



In the May-flies proper the same process was observed ; 

 the imago or perfect insect bursting its case about the same 

 time and in the same manner. 



As regards the change from the nymph to the sub-imago 

 state, amongst the smaller genera it is difficult to detect the 

 exact moment of the change, but with the larger species 

 (May-flies) the nymph rises to the surface, and it is often 

 some little time before it can free itself from its nymph- 

 covering (shuck), floating and fluttering along the surface 

 of the water for a few moments before rising in the air. 

 It is then that its life is so often cut short by the greedy 

 trout. 



The rise of the nymph of the May-fly from the bed of 

 the river appears to be very uncertain, and from our obser- 

 vations does not so much depend on the state of the 

 atmosphere as is supposed. Sometimes it would appear in 

 considerable numbers as early as 9.30 A.M. On other days 

 (these observations were made in 1885) it would be much 

 later the temperature of air and water being the same in 

 both instances. The effect of the sun's rays on the hatch 

 was very variable. On one cold blustering day, towards 

 the afternoon, the rise was something extraordinary, swarms 

 of the fly pervading air and water. On another day, with 

 a warm sun, the hatch was but small. 



May-flies remain attached to the under-surface of the 

 leaves both of trees and bushes during the early hours of 

 the day. But generally between two and three o'clock, 

 whatever might be the state of the atmosphere, most of 



