Vol. XXVl] ENTOMOLOGICAL NEWS II 



IV. EXPERIMENTS TO DETERMINE THE EFFICIENCY OF SHELTER 



AS PROTECTION AGAINST ENEMIES. 



Since it is well known that Odonate nymphs have enemies 

 such as fishes, waterbugs and larger nymphs of their own kind, 

 and, since most of them seek shelter in the mud, sand or weeds, 

 the question of the effectiveness of this shelter is a vital one. 

 Vegetation is the universal source of shelter. In the sub- 

 merged meadows about Ithaca Elodca, Myriaphyllum and 

 Potamogeton are among the typical water weeds, and these 

 were selected for the experiments. 



Apparatus (Plate I, Fig. 2). In order to control the ani- 

 mals in as natural a habitat as possible, a small part of Casca- 

 dilla Pond was fenced off with barbed wire, and a bridge of 

 logs and planks built to render this little "pasture" easy of 

 access. Within the enclosure a rough table and stool were 

 set up so that work might be conveniently carried on. 



Five cages were marked and placed in the pond with a space 

 between each two equal to the width of a cage. Each one 

 had a zinc bottom ten inches square upon which was soldered 

 a band of galvanized wire gauze, which formed the sides 

 eleven inches in height. The top was left uncovered. Each 

 cage was submerged to a depth of nine inches, thus allowing 

 the sides to project five inches above the water, which was 

 sufficient to prevent the animals within the cage from getting 

 out and those in the pond outside from getting in. Some very 

 small Chironomids, Amphipods, et cetera, could get through 

 the wire, but these did not affect the results. 



In the first set of experiments the common water weed, 

 Elodea, provided shelter. The plants were washed thoroughly 

 and then carefully examined by placing them in water in a 

 white porcelain tray to make sure that no damsel-flies or other 

 animals were in hiding. 



Cage i was left empty. Three twisted wire bars were placed 

 horizontally and at equal distances from each other in cage 2. 

 To each one of these, three plants were tied, the distance 

 between them being made equal to the expanse of the leaves 

 of the plant. The bars acted as weights, thus holding the 



