MAY-FLIES. 29 



the mud, and washing any suspicious-looking moving 

 object in a small net. When a larva is thus found and 

 afterwards liberated in the open water, it swims rapidly 

 for a few seconds, and then immediately begins to again 

 bury itself in the sand or mud. This is done by means 

 of the powerful head, jaws, and anterior legs. One 

 specimen I watched whilst thus engaged completely con- 

 cealed itself in less than five minutes. As these larvae 

 spend nearly all their time underground, they can be 

 devoured by fish only during emergence or as perfect 

 insects. It is therefore probable that the permanent 

 preservation of this May-fly larva in our rivers and 

 streams is fully assured. 



Unlike most other May-fly larvae, this insect is 

 extremely hardy, and can endure severe vicissitudes. 

 On one occasion a specimen was accidentally left for 

 a month in a tightly corked bottle with a little sand and 

 water, but when it was liberated it appeared none the 

 worse for its long imprisonment. 



Although difficult to find, this larva evidently occurs 

 in great profusion in certain localities. For instance, in 

 the Wainui-o-mata Kiver, about Christmas-time, the 

 nymph skins may be seen in hundreds, and the perfect 

 insect is very common there also. 



I once observed a larva of this insect just about to 

 emerge. It appeared very sluggish, and a large quantity 

 •of air was visible under the skin. The insect allowed 

 itself to float slowly down the stream just below the 

 surface, its gills working as rapidly as usual. Suddenly 

 the skin of the thorax broke open at the back, and in 

 two or three seconds a beautiful female sub-imago was 

 standing on the water alongside the empty floating pupa 

 skin. The rapidity of the transformation was marvel- 

 lous, the May-fly only appearing to shake its wings once 

 before they attained their full size. 



The sub-imago of the male of J. hudsoni differs from the perfect insect 

 in the following respects : The body is dull brown, the anterior legs are 

 very much shorter and stouter, and the tails are not quite so long as the 

 body. There are two conspicuous dusky transverse bands on the fore- and 

 hind-wings. The female sub-imago has the body pale yellowish-red, with 

 the tip of the abdomen blackish. The three tails ai'e equal in length, but 

 very short. The fore-wings have two conspicuous broken blackish, trans- 

 verse bands ; the hind-wings have a narrow blackish band near the base, 

 followed by two broad blotches near the edge of the wing. 



The sub-imago rests amongst foliage on the banks of 

 the stream for about thirty-six hours before changing. 



