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This illustration is taken from a photograph of a specimen lent to me by Mr. F. M. Halford, and both the fish and the larva were alive when they were caught. Unfortunately the trout is a little shrivelled, and the legs of the Dytiscus have been broken. D. marginalis lays its eggs in the stems of rushes. The larva, when hatched, makes its way out, and proceeds to lead a predatory life.

My whole batch was devoured one year by "devils" the larvæ of Dytiscus marginalis, the Plunger beetle. I have benefited, or at least have puzzled my neighbours also by introducing to them another sort of frog. Three years ago I bought twenty-five Hyloe, the pretty green tree species, to dwell in my Odontoglossum house and exterminate the insects.

The adult D. marginalis itself is not a whit less voracious, and much stronger than its larva. If the wooden parts of the apparatus have been properly prepared, according to my previous instructions, there should be no risk of the fry developing fungus.

He knew my advantages as well as I knew them myself, and bore me no ill-will for them. "The Dyticus marginalis, or Great Water-Beetle," I have heard him say, in the handsomest manner, "is equally at home in the air, or in the water. Like all insects in the perfect state, it has six legs, of which the hindmost pair are of great strength, and fringed so as to serve as paddles.

Among the worst enemies of both ova and fry is the Dytiscus marginalis, whether this insect be in the larval or adult stage. I think that I should hardly be wrong in going even further and saying that D. marginalis is very dangerous to trout early in their yearling stage. The accompanying illustration shows a larva of Dytiscus which has caught a young trout.

The claws, with which Hydrophilus seizes its prey, are, too, considerably smaller than those of Dytiscus. This larva should be kept out of the rearing ponds with just as much care as that of the more voracious D. marginalis. With the kingfisher I have already dealt at some length, so that I need say but little more with regard to it.

This beetle is not, in the adult stage at least, carnivorous, but the larva, which is about half an inch longer and considerably fatter than that of D. marginalis, is carnivorous. It may be told from the larva of Dytiscus not only by its size, which is hardly a reliable point for discrimination, but by the smaller size of the head in comparison to the rest of the body.

The greatest care must be taken not to introduce, or allow to intrude, any water beetles or the larger carnivorous aquatic larvæ of insects, into the rearing boxes. I have known cases where the larvæ of the Dytiscus marginalis, the largest of our carnivorous water beetles, have destroyed almost all the fry in a rearing pond.

It is generally advisable to avoid water-beetles, as most of them are more likely to do harm than good, such a number of our water-beetles being carnivorous. They will probably not harm adult fish, but they will destroy ova and fry. I have known a Dytiscus marginalis kill a trout of nearly a quarter of a pound in weight.