ths, and as many of them have their wings thickly covered
with hairs, this resemblance is sometimes very marked. The larvae
(caddis-worms), being eagerly sought as food by many fish, and having
very soft bodies, make for themselves cases. Some of these cases are
made from small sticks, some from little pieces of stone or sand, and
some from a mixture of all of these substances. As these cases resemble
such small pieces of rubbish as are frequently found in streams, care
should be taken that they do not get into the hatching trays containing
ova.

Many of the water beetles, and practically all of their larvae, will
attack the ova; they should therefore be carefully excluded from the
hatching trays. As there are about 114 different species of beetles in
the family of _Dytiscidae_ alone, my readers will appreciate my reason
for not attempting to enumerate them. It will be a sufficient warning to
state the fact that they are all carnivorous, and their relative sizes
is the only thing which will decide whether the beetle will eat the
fish, or the fish the beetle.

Very similar to beetles are some of the water-bugs. They may, however,
easily be distinguished from beetles, as the outer or anterior wings of
the bugs cross each other at their lower ends, while the elytra of
beetles, which much resemble the horny, anterior wings of some of the
water-bugs, meet exactly in the middle line. These water-bugs, though
some of them are excellent food for even the small fish, will attack the
ova, and therefore they should be kept out of the hatching trays. The
fish culturist should, however, whenever it is possible, cultivate such
of these water-bugs as are good food for the fry in separate ponds, as I
have before recommended. The best of these water-bugs are _Corixae_.
Others, such as the water-boatman, water-scorpions and pond-skaters, are
not of any value as food for the fish.

The larvae of _Ephemeridae_ are very good food for the fish, and should be
cultivated in separate ponds if possible, and some turned into the ponds
containing the little fish occasionally. A fair proportion should,
however, be kept in the ponds and protected, so that a good stock of the
flies may be available next year.

The larvae of _Ephemeridae_ may be obtained in many streams, and are best
caught with a fine gauze net. Some of them swim, but most are generally
captured with such a net at the bottom of the water among the _debris_.
Eggs of _Ephemeridae_