CADDIS-FLIES. 69- 



late autumn and winter they are very small ; cases taken 

 in June being less than ^ inch in length, although they are 

 quite as numerous then as at any other time. During the 

 spring the larvae gradually increase in size, and enlarge their 

 •cases accordingly, about the end of November; when most 

 of the streams have very much diminished in volume and in 

 rapidity of current, these insects speedily develop. They 

 probably feed on vegetable matter, and the green slime- 

 weed, which always grows profusely in slow-running 

 streams, forms, no doubt, their chief article of diet. This 

 •caddis-worm constitutes an extremely important item in 

 the food supply of trout, very large numbers of the cases 

 and their contained larva being found in the stomachs of 

 these fish. (See tables on pages 93 to 98.) 



The length of the larva of this insect, when extended, is about -^ inch. 

 The head is large, very broad, but short, blackish-green, with a few irregular 

 paler green marks. The prothorax is elongate, pale olive-green, with four 

 round black dorsal spots. The rest of the body is very pale olive-green, 

 marbled with darker olive-green, especially on the back. The surface is 

 much wrinkled. Anterior legs short, moderately stout, with a very sharp 

 single claw ; middle and posterior legs much longer and slenderer, apparently 

 employed exclusively in walking. Anal eminences very obtuse, each 

 furnished with about nine very stout bristles, and a minute but very stout claw. 

 Usual dorsal hump very small ; lateral humps also small. There are traces 

 of a few irregular, branching, white filaments. 



As soon as this larva is mature it firmly fastens its 

 •case to a large rock or stone in the stream, and, when 

 possible, always selects for this purpose a crevice in the 

 stone. A large number of larvae will frequently attach 

 their cases very close together in such a situation, and it 

 is most difficult either to detect or remove the cases when 

 they are thus protected by the overhanging edges of the 

 •crevice. Both ends of the case are, of course, closed with 

 the usual network, so that the enclosed pupa is securely 

 protected from all enemies. 



The perfect insect appears from November till 

 February. It must be very common, although it is not 

 often seen, owing no doubt to its small size, inconspicuous 

 appearance, and nocturnal habits. I observed it very 

 abundant on the banks of Lake Pukaki at evening dusk, 

 and further investigation will probably reveal its presence 

 in most places situated in the vicinity of water. 



PYCNOCENTRIA AUREOLA. 



Pijcnocentria aureola, McLachlan, Journ. Linn. Soc, 

 vol. 10, p. 200, pi. 2, fig. 4 (1870). 



