24 Flow to obtain tt. 
formidable claws, with which, if they once get hold, they seldom 
relinquish their prey until they are satiated. 
By way of experiment, six alevin trout were placed in a small 
tank along with two caddis worms, six with two large beetles, and 
six with two sticklebacks. The experiment was repeated several 
times with the same result ; the caddis worms killed more alevins 
in a given time than either of the others. Again, a tank was 
stocked with a mixed collection of insects, larvz, small fish, etc., 
and the conclusion arrived at was, that the large caddis worms are 
the most destructive of all. The large beetle larvae (Dytiscws) is a 
good second. They each settled minnows and sticklebacks, by 
gripping them from below. The caddis worms seem to be more 
active and more persistent in the chase, and their cases afford 
inconspicuous covers, constructed as they are from bits of their 
natural surroundings. The moral of this is that it is unwise to 
have any but very small specimens in fry ponds. 
The May flies, or £phemera, with which anglers are so 
familiar, and which seem in some localities to be steadily increasing 
in numbers almost annually, spend 
three years in the larval form in water. 
The perfect insects may be readily 
distinguished by their long tails and 
vertically folding gauzy wings. The 
larvee live in burrows in the muddy 
parts of the river bank, under water, \i eB 
and it is quite possible that this habit Le 
of burrowing may account for their 
extermination, by the increasing pol- 
lution of some streams. The very ; : 
E a c Fig. 31. Green Drake, 
lengthened sojourn of these insects in Ephemera aileariss 
the larval stage greatly tends to reduce 
their importance to fish culturists. This is no reason, however, 
for not planting them in districts where they have not hitherto 
occurred, and to which it may be deemed expedient that they 
should be introduced. 
The stone flies, the alder fly, the yellow Sally, the Spanish 
needle, the willow fly, and the gauze wing, are all well-known 
friends of the angler. They lay enormous quantities of eggs, 
