110 THE SCIENTIFIC ANGLER. 



Whirling Blue Duns,* do not occur anything like annu- 

 ally ; they prevail only during a spell of unseasonable 

 weather. A Dun of these pronounced shades may not 

 be observed for several seasons, whilst for some weeks in 

 the succeeding one it may be exceedingly prevalent. If 

 the range of shades previously described are correctly as- 

 serted to be dependent upon the state of the elements, 

 and therefore accidental, these latter are doubly so. 



The May-fly, Green Drake, or Cadow concludes the 

 order of up-winged insects. This fly is an annual one, 

 appearing upon the majority of trout streams about the 

 first week in June. Throughout Britain it may be said 

 to be in season from the middle of May to the middle of 

 June. These flies are often wondrously numerous. The 

 first four days or so when they begin to come up, the 

 fish seem rather afraid of them, but as they become more 

 numerous they are greedily taken. These flies are com- 

 mon for twelve or fifteen days, when they entirely disap- 

 pear until the next season. The fish so gorge themselves 

 during the drake season that they lie dormant for some 

 days before they are relieved from the effects of their ex- 

 cess. More has been written upon this than perhaps 

 any other fly. It has been set up as an analogy for the 

 lesser ephemeral orders, which is scarcely correct, as it 

 appears but for a limited period annually; and in the 

 second place the eggt remains in the water two years be- 

 fore it grows sufficiently, and has arrived at a proper 

 state of perfection to ascend. It is also longer lived as 

 a fly. Swammerdam speaks of it as "a being of a 

 day, whose life in a perfect state is compassed in a few 

 hours." Another affirms that "they lay about eight 

 hundred eggs immediately upon the wings being devel- 



* These flies are made here and used on our waters. 

 tThe larva. 



