WATER BEETLES IN RELATION TO PONDFISH CULTURE. 
251 
would mob together and seize the fish from different sides, and they kept up the 
attack until the fish succumbed. Of course, when the pond was lowered all its 
animal fauna was crowded together into a limited space, and the relations of the 
various species to one another became somewhat abnormal. If these larvae attack 
fish under such conditions, they might repeat the performance at another time, 
especially if their food supply became scarce. So far as known no other gyrinid 
larva has ever been reported as attacking fish. 
The haliplid larvae are all strict vegetarians and are so small and inactive 
that they do not catch any living animal, much less attack small fish. 
To summarize, therefore, the larvae of Dytiscus, Cybister, and Hydrous are 
known to eat small fish as a part of their regular diet. The larvae of Dineutes 
have been observed killing fish fry under somewhat abnormal conditions and 
might do the same thing whenever they had a chance. The larvae of Acilius and 
Hydrophilus are large enough to overpower very small fish fry, but thus far there 
is no positive proof that they actually do this. The other beetle larvae are too 
small to be reckoned as a menace to fish culture. 
With reference to the attacks made by adult beetles upon fish the testimony 
is much less satisfactory. Von Mentzschefahl in 1778-79 mentioned two species 
of adult water beetles (Dytiscidae) that attacked the perch in a pond in Silesia. 
Similar destruction of young fishes by adult water beetles was noted by Elies in 
1830, by Dale in 1832, by Riley in 1885, and by Dimmock in 1886. 
Elies wrote as follows (1830, pp. 148-149) : 
I observe that one of your correspondents notices the probability of ponds in elevated situations 
being stocked with fish through the agency of the water beetle. If this active and voracious little 
creature were really useful in that way, it might in some measure atone for its other mischievous pro- 
pensities; for I do not know a more destructive little insect to fish themselves, besides devouring the 
spawn. A neighbor of mine lost several hundred of the fry of the gold and silver fish by this little 
pest; and, to leave no doubt about the matter, he caught one and placed it in a large basin of water, 
to which he shortly after added a little fish. The beetle immediately made a dead set at the fish, which 
completely paralyzed the poor little animal, for it was soon after seized near the tail by the beetle 
without making any effort to escape, and never left until it was a perfect skeleton similar to numbers, 
that he had previously found. 
Elies gave no hint as to the genus and species of this beetle, although the 
query was made by a correspondent in Volume IV of the same magazine, and 
Elles’s attention was called to it by Dale on page 668 of Volume V. 
Riley stated (1885, p. 311) : 
The large water insect which attacks and kills young carp is evidently some species of Cybister 
or Dytiscus of the coleopterous family Dytiscidae. 
Dim mock’s testimony was quite different; he said (1886, p. 357) : 
I have seen a dead rat in a small pond surrounded by a great swarm of these beetles (Dytiscidae) 
and they prefer such food to living food. 
Garman said (1890, p. 163) : 
Both adults and young (Dytiscidae) lead a predatory life, attacking and devouring whatever they 
can master. They do not hesitate to attack animals many times larger than themselves and are very 
destructive in fishponds to young fishes. They are in turn eaten by the larger fishes. 
