DRAGONFUES AND DAMSELFUES IN PONDFISH CULTURE. 209 



fined to the warmer months, when they are present in greater numbers. The abundance 

 of Crustacea in the Fairport list will thus depend somewhat upon the fact that all the 

 nymphs were examined during the months of July and August. 



Conclusions. — Comparing the three food lists here presented from widely sepa- 

 rated localities, it would seem that odonate nymphs eat very much the same food 

 everywhere. They feed largely upon insects and are able to confine themselves practi- 

 cally to a single species that happens to be abundant, as in Hav/aii, or they may extend 

 their diet to include a rich variety of genera and species, as in the other two lists. In 

 her text notes Miss Lyon enumerates 11 species that could be identified amongst the 

 Chironomid larvae, with the probability that still others were represented in the 

 unidentified material. 



Judging from the lists, odonate nymphs do not devour many mosquito larvae or 

 pupae, although Warren (191 5) was firmly convinced that the Hawaiian nymph was a 

 great destroyer of mosquitoes, in spite of the unfavorable showing of his list. He even 

 fed some of his nymphs with mosquito larvae and adults. One Pantala nymph ate 

 during a single night 40 imagos of Stegomyia scutellaris that had been stunned with 

 cyanide fumes and placed in the aquarium with the nymph. Another Pantala nymph 

 ate 75 full-grown mosquito larvae within 12 hours. But here, as in the eating of the 

 fish, no convincing argument can be drawn from what is fed to a nymph when no other 

 food is available. 



The food of the odonate nymphs is by no means confined to insects, however; 

 they also eat quantities of Crustacea and mollusks and may include protozoa, algae, 

 and even vertebrates in their diet. In fact, the nymph seems capable of accommodating 

 itself wonderfully well to its environment and can seemingly thrive upon whatever 

 form of food happens to be available. Consequently if the nymphs are introduced 

 into a fishpond, no special food will need to be provided for them. If the pond is 

 stocked with the usual insect larvae, Crustacea, etc., whatever the species may be, the 

 nymphs will quickly adapt themselves to them. 



ENEMIES OF ODONATE NYMPHS. 



1. Fish. — A full discussion of nymphs as food for fishes is given on page 225. 



2. Larger Nymphs. — The proportion in which the smaller nymphs are destroyed 

 by the larger ones is well shown in the table and statements already given. 



About 20 per cent of the food of Anax nymphs and 10 per cent of the food of the 

 nymphs of L. luctuosa consist of other nymphs smaller than themselves. In general, 

 the nymphs that are eaten belong to a different genus, but the large nymphs are can- 

 nibalistic as well as rapacious and sometimes eat others of their own species. This 

 is not as likely to occur, because all the nymphs of a given species develop at about the 

 same time and are consequently nearer the same size. But they always vary more or 

 less in their rapidity of growth, so that some are larger than others, and even if two 

 were of the same size it would not be safe to keep them together unless plenty of suitable 

 food were provided for them. If they once became real hungry, they would fight it 

 out and the stronger would devour the weaker. To protect themselves against one 

 another, as well as against all their enemies, the Gomphid nymphs habitually burrow 

 in the mud or debris of the bottom; L. luctuosa and the heavier Libellulids sprawl 



