14 ENTOMOIvOGICAL NEWS [Jan., '15 



Cage 2, containing 2 bars with 2 plants each, displaced 30 

 cc. water. 



Cage 3, containing 3 bars with 3 plants each, displaced 60 

 cc. water. 



Cage 4, containing 5 bars with 5 plants each, displaced 150 

 cc. water. 



Cage 5, packed, displaced 475 cc. water. 



From the various combinations of shelter and enemies in 

 the experiments recorded here, the following results were ob- 

 tained : 



1. Dense growths of water weeds but ineffectively protect 

 damsel-fly nymphs from dragonflies. The results were irreg- 

 ular, the shelter at one time efficient, at another inefficient. 

 This might be expected from their similarity in habitat and 

 the custom of the dragonflies to catch their prey as they climb 

 slowly over the weeds. 



2. Vegetation of varying density provided a more effective 

 shelter from Dytiscid larvae. There were cases in which the 

 degree of shelter had no influence. Dytiscid larvae are more 

 likely to seek prey at the surface or on the bottom than in 

 midwater. This accounts for irregularities of results here, 

 since even in the empty cage the damsel flies would climb 

 about on the sides of the cage. 



3. In every case except cage 2, where the vegetation was 

 very scanty, it was a shelter against fish, the shelter becoming 

 more efficient with increased density. Fish are undoubtedly 

 among the worst enemies of damsel-flies ; examination of the 

 contents of fishes' stomachs has repeatedly shown this. The 

 protection afforded by dense aquatic vegetation has then an 

 enormous effect on the economy of the life of damsel-flies. 



Bibliography. 



1893 Calvert, P. P. — Catalogue of the Odonata (Dragonflies) of the 

 vicinity of Philadelphia. Trans. Amer. Ent. Soc. XX, pp. 

 152-272, 3 pis. 



1888 Forbes, S. A. — Studies of the Food of Fresh Water Fishes. 

 Bull. 111. State Lab. Nat. Hist. Vol. II, Art. vii, pp. 433-473- 



1905 JoHANNSEN, O. A. — May Flies and Midges of New York. Aqua- 

 tic Nematocerous Diptera II. Chironomidae, Bull. N. Y. 

 State Mus. 86, pp. 76-310, pis. 16-26. 



