WATER BEETLES IN RELATIOI^ TO PONDFISH CULTURE. 



267 



^ RELATIVE IMPORTANCE OF SPECIES. 



In these tables the Haliplidse are represented by 5 species, the Dytiscidse by 22, 

 the Chrysomelidae by 1, the Gyruiidse by 5, and the Hydrophilidse by 20, a total of 53 

 species. Many of these, however, as just stated, are so rare or occur in such small 

 numbers that they do not enter at all into the ecology of the fishponds. Once 

 listed as having been found and identified with reasonable certainty, they may be 

 conveniently dropped from further consideration without affecting at all the ulti- 

 mate results. vSuch a procedure reduces the number of species that really deserve 

 consideration so much that they can be intelligently and profitably discussed 

 within the limits of a single paper. On this basis there will be left 2 haliplids, 11 

 dytiscids, 2 gyrinids, and 10 hydrophilids, a total of 25 species out of the 53 enu- 

 merated. With these, mention should be made of the chrysomelid (Donacia 

 aequalis), both the adults and larvae of which are common in nearly all the ponds. 

 The adults are only semiaquatic and are found upon the leaves and stems of pond 

 lilies, arrowhead, pickerel weed, reeds, and sedges, while the larvae live upon the 

 outside of the submerged roots of these plants. Both larvae and adults are eaten 

 freely by fish. 



SYSTEMATIC DESCRIPTIONS OF FAIRPORT SPECIES. 



The part that follows is as much for the ordinary fish-culturist as that which 

 has preceded. Having convicted three of the prisoners brought before the bar, 

 justice demands that their likenesses and individual descriptions, as well as their 

 criminal records, be published, so that they may be recognized whenever they 

 attempt any nefarious work. The fish breeder, if he desires success, ought to be 

 able to tell these offenders at sight and so guard against their depredations. The 

 easiest method of doing this is to become familiar with their pictures and habits. 

 With this object in view, photographs of an adult Cybister, an adult Dytiscus, 

 and an adult Hydrous are here presented (figs. 1, 2, and 3, frontispiece). These 

 are the only genera whose adults kill fish fry, and the photographs will constitute 

 a sort of rogue's gallery for the fish-culturist. There is no necessity of determining 

 the particular species. Any beetle that lives beneath the water in a fishpond and 

 comes to the surface to breathe is a water beetle, and if it resembles any of these 

 figures in size and shape it may safely be condemned and destroyed. 



A fully developed larva of any of these three genera can be told by its size, but 

 younger stages are not as readily identified. The best means of recognition is the 

 head, and for that reason there will be found on the following pages an enlarged 

 figure of the head of each larva described. These give enough detail for identi- 

 fication, because the individual characters remain practically the same throughout 

 the life of the larva. The half-grown or quarter-grown larva may be recognized in 

 this way with nearly as much certainty as after it becomes fully matured. 



It is not, of course, intended that the average fish breeder should become a 

 systematic entomologist; that is not necessary. He may be fortunate enough 

 never to have occasion to identify any of these beetles either as larvae or as adults. 

 Should such a necessity arise, however, the figures here given will afford a quick 

 and ready means of recognition. Unfortunately, none of these larvae or adults 

 have a common name except the larvae of Cybister and Dytiscus, which are called 



