MAY-FLIES. 39 



habit ; and although the nymph is often very common in 

 favourable localities it is very hard to see. 



The food of the larva probably consists of minute 

 particles of vegetable matter, which it finds among the 

 stones. The best method of obtaining specimens of this 

 larva is to carefully sweep with a small net against the 

 current over the shallow rapids, which the insects fre- 

 quent. In this way two or three specimens may often be 

 secured at once in a stream, where perhaps the presence 

 of the insect was never suspected. Whilst sweeping, half 

 of the net should be kept above the surface of the water, 

 as I have noticed that if. a larva is approached in deep 

 water it invariably rises upwards and darts away with 

 great rapidity above the net. This habit would, no doubt, 

 often enable it to escape when pursued by a fish, as a 

 sudden movement above the fish would be very difficult 

 for the pursuer to quickly follow. 



The greatest number of mature larvae are found in the 

 streams during December and January. In February 

 there are still a few full-grown specimens, but in June I 

 observed that the nymphs of this May-fly were all very 

 small, measuring about £ inch in length. They are, 

 however, equally active at that season, although of course 

 the water is very much colder than in summer. 



The length of the full-grown larva, including the tails, is | inch. Its 

 general colour is obscure grey, mottled with darker, mature specimens being 

 almost slaty black, but young larvae are nearly transparent. The head is 

 small, the thorax rather broad, with the wing-pads large and conspicuous. 

 There are seven pairs of small oval gills, situated on the sides of the 

 abdomen, the insertion of each gill being marked by a black dot. The tails 

 are about two-thirds the length of the abdomen. They are fringed with 

 strong hair throughout, and their colour is pale greyish-ochreous, except the 

 middle half of each tail, which is black. The legs are rather short, and are 

 striped with black. 



The emergence takes place in the usual manner, the 

 nymph selecting for this purpose a dry stone close to the 

 edge of the stream. During December and January very 

 large numbers of the empty nymph skins may be observed 

 on the stones, showing that the insect actually exists in 

 large numbers, although not often observed. 



The sub-imago has the body rather stout, the two outer tails about the 

 same length as the abdomen, the central tail very short, and the wings are 

 prettily marbled with black in the male and dull green in the female. It 

 will thus be seen that the close resemblance of this insect to C. humeralis 

 exists during the final condition only, the insect's characters in its prepara- 

 tory stages, including the sub-imago, being very different to the correspond- 

 ing stages of that species. 



