ENEMIES OF MOLLUSCA — FISHES AND INSECTS. 419 
plant had been quite impossible. The Frogs and Newts also eat the 
different .species of Limnwa and Planoi'bis of our ponds and streams. 
Fish in general are very partial to the mollusca, feeding greedily 
upon them, and the havoc thus caused amongst the marine species by 
the enormous numbers they consume has been frequently chronicled, 
but the destruction amongst the freshwater species has not attracted 
so much attention. 
The beneficial effect of water-snails as nourishing food, especially 
for trout, is shown by the rapid growth of fish placed in streams or 
ponds in which mollmsks abound. The ravages of fish amongst mol- 
lusks are not, however, confined to such species as di.sport themselves 
more or less actively at the surface or amongst the vegetation, but is 
also carried on amongst the minute mud-loving Pisidia, which in 
America have been shown to be an important food of the Whitefish. 
The Gillaroo Trout, which lives in the Irish loughs, and other famous 
breeds also, subsist chiefly upon mollusks which give them the 
exquisite flavour which has rendered them so famous and prized by 
epicures. Specimens of the Gillaroo Trout have been caught gorged 
to repletion with Blthynki tentaciilata and other fre.shwater species, 
and the remarkable and peculiar thickening of the stomach-walls of 
this trout has been attributed to the fact of shelled snails forming so 
large a part of its diet. 
The Eel is another rapacious devourer of the mollusca, as many as 
350 shells of Valvata piscinalis, in addition to those of other species, 
having been obtained from the stomach of a single eel. 
The Barbel has been noted as having a special predilection for 
Vdlvata i)iscin(dis and also for Sphivrium corneum, and many fi.sh, 
and more e.specially gold carp, regard Physa fontmalis as a choice and 
delicate morsel, while the Boach is recorded to feed even upon the 
eggs of the various species. 
The CoLEOPTERA prey freely upon the mollusca, the Dytisciis 
marginalis being particularly destructive to the Limufeidfe generally, 
but apparently preferring Limnceci stagnalis to other species, although 
accumulations of the shells of Planorbis corneus with the sides of the 
whorls bitten aw'ay, to allow of easy access to the animal, have been 
recorded as the work of this species. 
The Silphidte also destroy the smaller land .species, the Rev. A. H. 
Cooke stating that they fracture the shells by striking them against 
their own prothorax. 
