DRAGONFUES AND DAMSELFLIES IN PONDFISH CULTURE. 



20I 



Such a conclusion is, of course, not warranted, and even with reference to ^Eschna 

 itself it does not follow that it must be considered dangerous simply because it eats a 

 few small fish. Needham (1903, p. 213), one of our most experienced observers, said 

 with reference to jEschna constricta, which was common at Bone Pond, one of the three 

 propagating ponds controlled by the Adirondack hatchery in New York, and artificially 

 stocked with brook trout: have not been able to determine as yet whether in rela- 

 tion to trout culture ^schna is more disadvantageous than otherwise. It eats a few 

 fry and it eats the food of the larger trout, but, on the other hand, it furnishes a moderate 

 supply of food itself for the larger trout." In order to solve such a problem satisfactorily 

 we must consider in detail all phases of the economic relations between odonates and 

 fishes. An endeavor to do this has been made in the following pages by a careful con- 

 sideration of the food and enemies of dragonfly and damselfly nymphs and imagos, 

 by a summary of all that is known of nymphs and imagos as fish food, and by extensive 

 observation and experimenting. 



FOOD OF ODONATE NYMPHS. 



The alimentary canals of 50 nymphs of each of the four dragonfiies enumerated in 

 the following table and 50 others of various damselfly species, making 250 in all, were 

 examined to ascertain what food had been eaten. The presence in a nymph's digestive 

 tract of any of the various kinds of food listed was represented by a single unit, whether 

 found in large or small quantities. The figures in the table, therefore, tell us how 

 many of the nymphs had eaten any specified food, but do not indicate how much they 

 had consumed. 



Food oif 250 Odonatk Nymphs from Fairport, Iowa. 



[The figures indicate the number of nymphs in which each.kind of food was found.] 









jlicicolUs. 



igipenni5. 



phs. 









)Ucicollis. ij 



igipennis. 





Contents of alimentary canal. 



Anax jimius. 



lyibellula luctuc 



Erythemis simj 



Pachydiplax loi 



Damselfly nym; 



Contents of alimentary canal. 



Anax Junius. 



1 



Si 

 A 



1 

 1 



u 



Pachydiplax loi 



Damselfly nymj 



MoUusca : 



Physa shells, mostly fragments 



16 



6 



16 



4 



8 



Crustacea — Continued . 



Simocephalus, sp 





2 







8 



Planorbis shells, mostly fragments . . 

 Beetles: 



34 





12 



Daphnia, sp 



5 

 2 





2 



4 

 4 



17 

 5 



15 





4 













5 



Dytiscus larvae 



10 



8 



2 



2 





Copepods, fragments unidentified . . . 







3 





IS 

 6 



Haliplid beetle, elytra of adults 



8 



3 



8 



12 









I 



4 



4 



Peltodyes larvae, jointed hairs 







6 







Hyalella, sp 









I 





Diptera: 





















2 





Ceratopogon larvae 



2 





6 





2 



Odonata: 













Chironomid larvae 





3 



5 





8 



Damselfly n^Ttiphs, unidentified 



II 



IS 

 3 





2 



2 



Mosquito larvae 





I 





3 

 I 



6 



Ischnura verticalis nymphs 



12 



2 



I 





Simulid larvae 







8 



4 



9 







2 



5 



I 





Hemiptera: Corixa, sp. , elytra of adult . . 

 Sialidae: Sialid larvae 



14 



3 



4 



3 



I 





Eestes, sp., nymphs 



6 



2 



4 



S 







2 







Libellula luctuosa, nymphs 



S 

















6 



2 







2 











Ephemerids: Mayfly larvae 



27 



9 



7 



4 



6 



Erythemis simplicicollis, nymphs . . 

 Algae: 



Desmids 



6 



4 



I 







Crustacea: 



Bntomostraca, fragments imidenti- 













9 



4 



2 



13 



fied 



5 





26 



15 



20 



Diatoms 







8 



2 



Cladoceran eggs, with ephippium . . . 



2 



7 



9 



6 



10 



Sponge spicules, in masses 





5 









3 



8 



6 



4 



12 



CEdogonium, scattered filaments 







6 



3 



14 



25 





6 



3S 







IS 



Algae filaments 



7 



7 



32 





















