Flow to obtain it. 213 
as it is one that is well known to all observers, and that is the 
little whirlygig beetle (Gyzinus natator), so called because it 
swims round and whirls about on the surface of the water. It is 
rather curious in structure, an excellent swimmer, and provided 
with top and bottom eyes, so to speak, so that it can see either a 
bird above or a fish below, if they approach with hostile intentions. 
It also emits an oily fluid if attacked, and has a very disagreeable 
smell. Its food, so far as we have observed, appears to be flies 
and gnats just emerging from their larve on the surface of the 
water ; at all events it pounces on these with avidity. 
We may now consider a few of the flies that spend their 
larval period in water. They form in most cases a very consider- 
able portion of the natural supply of fish food. Two of the chief 
families of such flies are the caddis flies, or Z7cchoptera, and the 
Neuroptera, or nerve-winged flies. There are some two hundred 
varieties of caddis flies, or ‘ water moths,” as they are sometimes 
called, one of the largest and most typical being the Prrvganea 
Fig. 30. Caddis Fly, Phryganea grandis. 
grands of the entomologists, or the “ brown owl” of the angler— 
so called because of its brown russet colour and soft downy wings. 
The caddis flies lay a considerable number of eggs, sometimes in 
the water on aquatic plants, and at other times on marginal plants, 
whence the young larvee, on hatching, have to find their way into 
the water as best they may, many doubtless perishing ev route. 
Once in the water the larvee clothe themselves with bits of stick, 
stone, rush, leaf, sand, shells, or anything else they come across, 
forming a tube which serves the double purpose of a protection 
from their enemies, and also an ambush in which they can 
approach their prey unobserved. Their food consists chiefly 
of animal matter, dead or alive ; they are capital scavengers, and 
are excellent trout food, but the larger varieties are great enemies 
to the young fish, and they are provided with a pair of most 
