DRAGONFUES AND DAMSELFUES IN PONDFISH CULTURE. 



205 



Another so-called proof has been widely copied by both entomologists and fish- 

 culturists and appeared even in the Cambridge Natural History (Insects, 1901, pt. i, 

 p. 425). It was originally published in the Hungarian Rovartani Lapok for December, 

 1884, and consisted of a statement by L. Biro that in a pond belonging to the piscicultural 

 establishment of M. le Comte Palffy at Szomolony, Hungary, only 54 small fish could be 

 found in September, although 50,000 had been placed there the previous spring, but 

 there were present an enormous number of Libellulid larvae, species not determined. 

 Hence the nymphs must have eaten the fish. The simple facts, however, that the fish 

 were gone and the nymphs were present could hardly be accepted as scientific proof that 

 the latter ate all of the former or any part of them. There are too many other causes 

 which might have removed the fish. It was not even determined to what species the 

 n5rmphs belonged, none of them were seen eating fish, and no stomachs were examined 

 for fish remains. Then, too, the nymphs found in September, if they were Libellulids, 

 were hatched from eggs laid during that summer and could not have been large enough to 

 eat any fish. 



James G. Needham has two records of nymphs eating fish : In Aquatic Insects in the 

 Adirondacks (Needham and Betten, 1901, p. 474) he states that "nymphs of the species 

 described below as Cordulegaster maculatus supposition" captured and ate young trout 

 as long as themselves at Saranac Inn, when the trout were placed in their cage. In 

 Aquatic Insects in New York State (1903, pt. 2, p. 213) he says that the nymphs of 

 Mschna constricta eat a few trout fry, but he does not tell how this was proved unless 

 his statement on page 212, "I demonstrated this at Saranac Inn by confining them to- 

 gether in a breeding cage" is understood to apply to ^schna as well as to Cordulegaster. 

 That is no proof, however, that trout constitute any part of the regular diet of either 

 nymph mentioned, or of any other nymph. 



Warren (191 5) found that the nymphs of Pantala flavescens would eat practically 

 anything he gave them, even earth worms and chicken lice, but one would hardly care to 

 draw any argument from this fact. When confined together in a besieged fortress or 

 town human beings have been known to eat horses, dogs, or even one another. A nymph 

 must be observed actually eating fish under natural conditions, or fish remains must be 

 found in its stomach when captured, before anything can be really "demonstrated" 

 with reference to its normal diet. 



For this reason such pictures as figure 232 on page 389 of The Life of Inland Waters, by 

 Needham and IJoyd (191 6), are likely to be very misleading. The authors were there 

 discussing the forage problem in connection with fish culture, and introduced this picture 

 of the nymph of Anax junius devouring a small sunfish without a word of comment or 

 explanation. It is evidently a photograph and must have been taken under either natural 

 or artificial conditions. If the conditions were natural, we have a perfect right to know 

 it, because it would add greatly to the value of the picture; but if the conditions were 

 artificial, the picture never should have been published. In either event it is misleading 

 unless fully explained, because it gives the prospective fish breeder the idea that all 

 dragonfly nymphs eat small fish whenever they get a chance. The ordinary individual 

 will comprehend the words "nymph" and "dragonfly," but the specific name, Anax 

 junius, will mean nothing to him. He will keep the picture and its implied testimony 

 constantly in mind during his subsequent fish breeding, and it will require long-continued 

 and patient efforts to correct its influence. It is unfortunate that this was not recognized 

 by the authors of a book so admirably designed and executed in its general features. 



