MAY-FLY FISHING. 353 



varying according to the temperature ; thus, in very cold 

 weather it has been found burrowing more than three feet in 

 the river-bed, in the early spring at a depth of about eighteen 

 inches, while at the commencement of June it is only an inch or 

 two below the surface. It is quite possible that this statement 

 may give rise to some controversy, and instances will be given 

 of these larvae being found in fast-running stickles, or shallows, 

 and on hard clean gravel, and on this evidence anglers will be 

 asked to discredit the careful observations of naturalists re- 

 peated over and over again for more than a century. There is, 

 however, no doubt that some considerable number of May-fly 

 larvae are from time to time found in rapid water where there 

 is not sufficient mud to cover them. This seeming anomaly is, 

 to my mind, quite capable of being explained. Every flood, 

 every cleaning of the river, every disturbance of the mud, 

 and every cutting of the weeds must of necessity set adrift a 

 certain number of larvae ; these are unable to progress against 

 or even across the stream, and the moment they find they are 

 being carried down, instead of exhausting their strength by 

 vain efforts to stem the current, they let themselves sink to the 

 bottom, and crawl along until they find a suitable place, in 

 which they once more commence their burrowing operations. 

 Hence the occasional presence of larvae on hard gravelly 

 scours; and, of course, the greater the number of May-flies on a 

 river, and the more frequent the causes of disturbance, the more 

 numerous are likely to be the occasions on which the larvae and 

 nymphs are found on what must be considered unsuitable 

 ground. 



After a certain number of moults the wing-covers attached 

 to the thorax become visible; at first they are transparent and 

 very small, but gradually grow larger and become darker in 

 colour as the development of the wings folded up within them 

 progresses. From the time of the first appearance of the wing- 

 covers the name nymph is applied to the immature insect, but, 

 beyond that it has grown larger and slightly darker in coloui, 

 and that the mouth organs and branchiae are further developed, 



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