271 The N.Z. Journal of Science and Technology. [Jan. 
In New Zealand the native may-fly fauna has been evolved without 
exposure to the attacks of rapacious fish such as the trout. There is only 
one large species whose larva burrows into the river-bank—viz., Ichthybotus 
hudsoni ; and it is clear, for many reasons, that this may-fly did not evolve 
this habit in New Zealand, but migrated thither long after the adoption 
of it. All the rest of the 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 Onisci- 
gaster, one of the finest may-flies in the world, sit about on rocks or on 
the gravelly bottoms of streams, and when attacked they only wriggle for¬ 
ward like a shrimp. Consequently they have become an easy prey to the 
introduced trout, which gorged themselves for some years on this large 
supply of choice food. This magnificent genus is now quite extinct through¬ 
out the Hot Springs region, and also in the streams around Christchurch, 
though still to be found here and there in out-of-the-way places in both 
Islands. Another fine genus, Ameletus, has larvae capable of quicker move¬ 
ment, 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 discover a single Ameletus larva throughout my investi¬ 
gations, though I caught a fine imago of a new species belonging to this 
genus above the high waterfall at Waihi, near Tokaanu, where trout are 
absent. A third may-fly genus of great importance is Coloburiscus. 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 
from all parts of the Hot Springs 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 may-flies, Atalophlebia and Deleatidium, containing numerous 
species which 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. Throughout the Hot Springs region a very 
considerable diminution of the supply of the small may-flies is noticeable ; 
and this cannot fail to exercise a serious effect upon the future of the 
trout. 
To sum up the position, we may say that the largest may-flies, which 
form the very finest possible food for trout, have been practically exter¬ 
minated, while the smaller forms have been reduced, at a moderate estimate, 
bv over 50 per cent. 
The Dragon-flies. 
New Zealand is poor in species of dragon-flies, 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 account. The larvae of the other five were 
all found by me in the stomachs of trout, the most frequently occurring 
