DRAGONKUES AND DAMSElvFLlES IN PONDFISH CULTURE. 211 



7. AivG-^, Fungi, and Vorticellids. — "The Confervoid alga, CEdogonium, is 

 often found growing upon the larva of jEschna brevistyla. I found by means of sections 

 that the CEdogonium does not penetrate the cuticle of the larva, but simply grows 

 on it as it grows on everything else in such places. On one larva of ^schna there were 

 no less than 3 species of CEdogonium, 15 species of Diatoms, and a large number of 

 Vorticella." (Tillyard, 191 7, p. 332.) CEdogonium is very common in several of the 

 ponds at Fairport and is found growing over many of the pond contents, including 

 nyftiphs, but it appears to do them no injury further than to impede their movements 

 slightly. 



Miss Lyon (191 5, p. 5) published a table giving the Diatoms, green and blue-green 

 algae, the protozoa, and the epizoa found growing upon the nymphs of Cascadilla Creek 

 She noted the similarity between these species and those of the mud and water plants 

 in the immediate vicinity. She concluded that the relationship between the two was 

 simply a natural one, resulting from the proximity of the various forms, and not one of 

 symbiosis, as Kammerer and others would have us believe. 



Similarly a Saprolegnious fungus frequently attacks damselfly nymphs, especially 

 if they are enfeebled from any cause. This fungus is related to the one attacking 

 young fishes and often causes the death of the nymph. (Garman, 191 7, p. 442.) 



8. Birds. — Needham has recorded dragonfly nymphs as found in considerable 

 numbers in the stomachs of herons (1898, p. 85). McAtee (191 2) also recorded nymphs 

 as forming part of the food of. the horned grebe, Colymhus auritus. But herons and grebes 

 and their kin are deadly enemies of fish, and hence should always be kept away from 

 fishponds. Under natural conditions, however, they might well consume a considerable 

 quantity of nymphs. 



9. Reptiles. — Martin (1886, p. 232) said with reference to the Odonata of the 

 Department de I'lndre in France: 



Thq eggs, larvae, and nymphs are the prey of several fishes, snakes, newts, Coleoptera, aquatic 

 Hemiptera, and of some diving birds. Sometimes the destruction is on a considerable scale, and one 

 may notice the dragonflies of some piece of water diminish gradually in numbers, while the animals 

 that prey on them increase, so that a species may for a time entirely disappear in a particular spot, 

 owing to the attacks of some enemy that has been specially prosperous and also eager in their pursuit. 



Baker (1906, pp. 231, 232) in his study of The Relation of MoUusks to Fish in 

 Oneida Lake found numerous dragonfly nymphs in the stomachs of painted terrapins, 

 Chrysemys picta. 



None of the terrapin at Fairport were examined for the food they had eaten, but 

 they may fairly be reckoned among the enemies of the nymphs. 



Ordinarily the dragonfly nymph is able to hold its own in spite of its enemies, 

 and it requires conditions exceptionally adverse to the nymph and exceptionally 

 favorable to its foes before there is any danger of the extermination of the nymphs. 



FOOD OF ODONATE IMAGOS. 



• There are several things which make it difficult to obtain specific lists of the food 

 of the imagos similar to those presented for the nymphs. 



A considerable portion of the animals eaten by the nymphs, such as snails, ento- 

 mostraca, beetles, hemiptera, and the like, are inclosed in hard shells or elytra, which 

 persist inside the digestive canal of the nymph and are easily recognized. The food 



