2o6 



BUIvIvETiN OF THE BUREAU OF FISHERIES. 



All the ponds of series D usually contain both Anax and i^schna nymphs, and 

 several of them contain young fishes. When the ponds are drawn, as is done for each of 

 them twice a year and sometimes oftener, the young fish and the nymphs, as well as all 

 the other denizens of the pond, are brought into close contact. At such times crayfish, 

 Dytiscus larvse, and the like have been repeatedly observed catching and eating small 

 fish, but no dragonfly nymph has been thus far seen attacking a fish. There is always an 

 abundance of other food for them, and they evidently prefer it. In further proof of this 

 1 8 Anax and ^schna nymphs were taken from ponds 7 and 9 on July 6, 191 6, when they 

 had attained their maximum size. Both ponds at that time contained an abundance of 

 small fish, but no fish remains could be found in the alimentary canal of the nymphs. 



Hence when an Anax or .^schna nymph does prey upon fish it may well be because 

 of a scarcity of other food. In evidence of this. Warren (191 5, p. 35) has recorded a very 

 interesting experiment. He placed 69 nymphs of Pantala flavescens and one of Anax 

 junius in a small aquarium and gave them no food except one young fish. At the end 

 of a week there w^ere left 7 Pantala nymphs, the Anax nymph, and the little fish. As 

 long as other food was present, therefore, the fish remained untouched. 



Furthermore, Warren examined the contents of the alimentary canal of 253 Anax 

 and Pantala nymphs and found fish in only one of them. (See p. 207.) Even there the 

 remains were so doubtful that he placed a question mark after his identification of them. 

 In a series of experiments made " with the view of finding out how far the food range of 

 the nymphs extended among the aquatic forms of life," he placed various aquatic animals 

 in the breeding jars and allowed the nymphs to eat them at their leisure. Among the 

 forms thus eaten were several kinds of fish, which were common in the localities from 

 whence the nymphs were obtained. Under natural conditions when other food was 

 abundant the fish were not touched, but when brought into the laboratory and deprived 

 of other food the nymphs ate the fish freely. 



Garman (i 91 7, p. 441 ) gave as one of the foods known to be eaten by damselfly nymphs 

 very young fish. No authority was given for this statement, and inquiry has revealed 

 that it was a mistake. We thus see that practically all the positive evidence shows that 

 when an Anax or ^schna nymph does eat a young fish it is because of a scarcity of other 

 food. Even if they do eat them occasionally they also eat enough Dytiscus larvse, 

 adult Corixas, Cypris, and crayfish to more than offset this. We must remember that 

 it is only with reference to a very few of the largest species that any claims are 

 made — 2 dragonflies out of the 27 on the present list. The other 25 and all of the 

 damselflies are admitted to be perfectly harmless so far as young fish are concerned. 



Amount of Food Consumed. — The nymphs are not only predatory and omnivorous, 

 but they may fairly be called voracious. They gorge themselves to the full extent of 

 their capacity, and the distended gizzard with its dark contents is often visible through 

 the skin and always stands out prominently when the thorax is opened. Usually also 

 the intestine behind the gizzard is filled out into a plump cylinder for 4 or 5 mm. with 

 finely ground indigestible material, such as the mandibles of insect larvae, fragments of 

 snail shells, broken elytra, etc. 



There is a great difference in the amount of food consumed according to the condition 

 of the nymph. Just after a molt the nymph is light in color, yellowish or greenish, and 

 shows a characteristic color pattern very distinctly. As development progresses toward 

 the next molt the color pattern gradually disappears, and the nymph becomes darker 

 and darker until, in L. luctuosa and E. simplicicollis , it turns to a uniform dark brown. 



