208 XEUROPTEROID INSECTS OF THE HOT SPRINGS REGION', X.Z., 



large May-flies, forming together a magnificent fauna unequalled in any other 

 part of the world, have evolved little or no protective habits against such a 

 fish as the trout. The larvae of Oniscif/a-ster, one of the finest May-Hies in the 

 world, sit about on rocks or on the gravelly Ijottoms of streams; and. when at- 

 tacked, they only wriggle foi-ward like a shrimp. Consequently they have become 

 un easy prey to the introduced trout, whicli gorged themselves for some years on 

 this large supply cf choice food. This magnificent genus is now quite extinct 

 throughout the Hot Springs Region, and also in the streams around Christchurcli, 

 though still to be found here and there in out-of-the-way places in both Ishmds. 

 Anotlier fine genus. Ameletus, has larvae capable of quicker movement, and is 

 therefore still fairly abundant in most parts of New Zealand. But these larvae 

 are also on the verge of extinction in the Hot Springs Region. I did not dis- 

 cover a single Ameletus larva throughout my investigations, though I caught a fine 

 imago of a new species belonging to this genus above the high waterfall at Wahi, 

 near Tokaanu. where trout are absent. A third May-fly genus of great import- 

 ance is Coliibrtrisciis. The larvae have a certain amount of protection against the 

 trout, owing to their bizarre form, their gills being arranged so that they look like 

 a small piece of tangled moss or weed. They are very sluggish and hide under 

 rocks and stones in running water. Coloburiscus humeralis is one of the most 

 abundant May-flies in New Zealand; yet it has been practically eliminated fr<im 

 all parts of the Hot Spring's Region, except only on the Tongariro River and its 

 tributaries, and on those small streams where trout are absent, from some cause 

 or other, such as the intervention of a high waterfall, as at Wahi. 



Besides the larger May-flies mentioned above, there are two genera of smaller 

 ■\[ay-flies, Atalophlehia and Deleatidium, containing numerous species whicli are 

 very abundant all over New Zealand. The larvae live under rocks and stones in 

 streams and lakes, and are fairly active. Most of them are vegetable feeders, 

 but a few are carnivorous. A number of species of these genera were collected, 

 some of 'them new to science. These latter will be described later. Througlioui 

 the Hot Springs Region, a very considerable diminution of the supply of the 

 small ]\ray-flies is noticeable; and this cannot fail to exercise a serious effect upon 

 the future of the trout. 



To svmi up the position, we may say tluit tlie largest May-flies, which lorm 

 the very finest possible food for trout, ha\-e been ])ractically exterminated, v.hile 

 the smaller forms Iiave been reduced, at a moderate estimate, by over 50 '"f . 



Tlie Dmgon-flies. 



New Zealand is poor in species of Dragonflies. but most of them are common. 

 Seven species are found very commonly throughout the Hot Springs Region. Of 

 these the largest {Uropetala carovei) is of no importance as trout food, the larva 

 dwelling in holes in the moss and peat of swamps. The larvae of the bright red 

 Diplacodes bipunctata, dwelling in still back-waters, may also be left out of ac- 

 count. The larvae of the other five were all found by me in the stomachs of 

 trout, tlie most fref|uently occurring being those of Procordulia smitliii, Pr. r/rai/i 

 and X(()itliiic»emis celandica. No doubt, later on in the season, the trout would 

 also feed upon tiie imagines, as in Tasmania. 



In certain parts of New Zealand. T found Dragonfly larvae to he the principal 

 food of the trout. In the Hot Springs Region, the trout seem to have consider- 

 ably diiiiinislied the number of larvae, and they do not form so important an 

 article nf diet, perhaps because they are more protected by their peculiar colour- 



