206 XEUROPTEROID IXSECTS OF THE HOT SPRINGS REGION, X.Z., 



cases, many of the larvae being still ali\e within the trout's stomach. Another 

 important food was a small Mollusc, Potamopyrrjus sp., of which no less than 140 

 ■were counted in the stomach of a "slab" taken at Rotorua. Other foods found 

 Jess commonly were the laiTae of Dragonflies, Mayflies, Stonefiies and the other 

 families of Caddis-flies, occasional remains of the Crayfish, small fish, and a 

 number of insects of various kinds which may be considered to have no definite 

 value as trout-food being only chance captures. 



Besides these, it is important to note that some trout-stomachs were found 

 containing nothing but pebbles, and several were quite empty. 



A considerable number of the trout examined were definitely "slabs." The 

 slabby condition appeared to be due, not only to the usual poor health of the fish 

 for some months after spawning had taken place, but more definitely to both 

 semi-starvation and indigestion. It was not surprising to find that fish with 

 their stomachs empty, or only filled with pebbles were in poor condition. But 

 there were also cases in which the slabby condition appeared to have been caused 

 by the indigestibility of the food. In one case the large claws of a crayfish were 

 found fixed inside the stomach of a trout in such a way as to block the passage 

 of other food ; and they had evidently been there a considerable time, seeing that 

 all the rest of the animal had been completely digested. This led me to conclude 

 that the crayfish is only a good food for trout when it is of not too large a size. 

 Consequently the introduction of any larger or more ^ngorous species of crayfish 

 than the one endemic in the region ought not to be encouraged. 



(ii.) The Neuropteroid Faux a of the Streams axd Lakes. 



The Neuropteroid Insects inhabiting the streams and lakes of the Hot Springs 

 Region may be divided into .six Orders, three of which belong to the more primi- 

 tive division of the winged insects, viz., those that have no true j>ui)al or resting 

 stage (Hemimetabola) and three lielong to tlie more higlily evolved division, pos- 

 sessing a true pupal stage (Hok)nietabola). Tliey may be classified as follows:— 

 Division Ilemimetdhola: (Winged insects without a true |)ui>al or resting stage). 

 Order 1. Perlaria or Stone-flies. 

 ,, 2. Plectoptera or May-flies. 

 ,, 3. Odonata or Dragonflies. 

 Division Uohniietabolu: (Winged insects iiossessing a true pupal stage). 

 Order 4. Megaloptera or Alder-Hies. 

 ,, 5. Planipennia oi- Lacewings. 

 „ 6. Trichoptera or Caddis-flies. 

 (^Xote. — The Scorpion-flies, Order Meooptera. ai-c not reiiresented in the 

 Region under discussion.) 



Of the six Orders enumerated we may omit from the discussion Order 5 

 (Lacewings) Avhose larvae are either terrestrial, or else lurkers along the moist 

 borders of streams. They attack the larvae of the other Orders wliich are 

 of value as food for trout. Thus, in so far as they affect the problem at all, 

 they act detrimentally to the food-supply. But they are exceedingly rare in the 

 Hot Springs Region, and were only found by me in two localities, viz.: Hanniiana 

 Spring, and the waterfall at Wahi, near Tokaanu. 



Order 4 (Alder-flies) is only repi'esented in New Zealand by a single species, 

 Arclmcliauliodes dubitatm, an insect of large size, whose fat, succulent larva is 

 found under rocks in streams, and forms an excellent food for trout. This larva 

 is called the "Black Creeper," or sometimes the "Toe-biter." Though very nbun- 



