1921.] Tillyard. — Neuropteroid Insects as Trout-food. 273 
in the Hot Springs region, and were found by me in only two localities— 
viz., Hamurana Spring, and the waterfall at Waihi, near Tokaanu. 
Order 4 (alder-flies) is represented in New Zealand by only a single 
species, Archichauliodes dubitatus , an insect of large size, whose fat, succulent 
larva is found under rocks in streams, and forms excellent food for trout. 
This larva is called the “ black creeper,” or sometimes the “ toe-biter.” 
Though very abundant in most parts of New Zealand, it appears to have 
been exterminated by the trout in most parts of the Hot Springs region, 
though it is still fairly abundant on the Tongariro River and tributaries. 
The other four orders—stone-flies, may-flies, dragon-flies, and caddis- 
flies—are of the greatest importance as trout-food, and we have to consider 
them in somewhat greater detail. 
The Stone-flies. 
These insects confine themselves to running water, preferring rocky 
streams with a fairly fast current. Their larvae live on rocks and stones, 
where they wander freely in search of food. The perfect insects, or imagines, 
are sluggish, and seldom fly, preferring to sit about on the vegetation over¬ 
hanging the streams. Nevertheless they frequently fall into the water, 
and are eagerly seized by the trout.- Both larvae and imagines are soft- 
bodied insects with a plentiful supply of fat, and form an ideal and easily 
digested food for trout. 
Except along the Tongariro River and its tributaries, where the stone- 
fly fauna is still abundant, these insects are very rare in the Hot Springs 
region ; and it is very clear that they have been greatly reduced in number 
by the trout. 
The large green stone-fly, Stenoperla prasina, generally abundant 
throughout New Zealand, and one of the best of trout-foods, was only to 
be found in streams above high waterfalls, where trout were absent. It 
has been almost completely annihilated in the Hot Springs region. 
The black stone-fly, Austroperla cyrene , the most abundant stone-fly 
throughout New Zealand, has likewise been almost eliminated by the trout. 
A colony of larvae was discovered at the extreme head of one of the small 
streams at Hamurana. There are also a few larvae left here and there in 
the Tongariro River. 
Of the slender stone-flies (family Leptoperlidae) a number were found on 
the Tongariro River and its tributaries. Some of these are new to science, 
and will be described later. But, generally speaking, it may be said that 
these valuable flies, like the rest of the Perlaria, are on the verge of 
extinction in the Hot Springs region. 
It would, I think, be well within the mark to estimate that more than 
80 per cent, of the original stone-fly fauna of the region has already been 
destroyed by the trout. 
The May-flies. 
These insects inhabit both streams and lakes. In all parts of the 
world they form one of the most important articles of diet for the trout. 
Both the larvae and the imagines are soft-bodied and easily digested. In 
the Northern Hemisphere, where the evolution of the mav-flies has taken 
place alongside that of the native trout, the larvae have resorted to many 
cunning devices in order to escape their rapacious enemies. Those of the 
larger species mostly burrow into the banks of streams, and thus secure 
immunity from attack ; while the smaller forms hide under rocks and 
stones, and evade attack by their quick-running powers. Thus the trout 
only secure the may-flies in their winged stages (subimago and imago). 
