FIELD BOOK OF PONDS AND STREAMS 



petitors for the same food, but dragonflies are themselves one 

 of the most important foods for adult fishes — pickerel, perch, 

 catfish, and small stream fishes (Fig. 21). An insight into 

 the dangers which greet the nymphs from their earliest youth 

 is given in an observation made by Dr. C. B. Wilson. "Two 

 leaves of Potamogeton illmoisensis, which contained a large 

 number of Enallagma eggs that were just hatching, were 

 brought into the laboratory August 11, 1917, and placed in a 

 small aquarium. On going over them with a hand-lens to 

 remove the nymphs already hatched, a large brown hydra 

 was found eating one of the tiny nymphs. It was attached 

 to the under surface of the leaf, nearly in the center of a large \ 

 cluster of Enallagma eggs, and could reach many of the 

 nymphs with its tentacles as they emerged." 



Aquarium study. — The nymphs of most pond dragonflies are , 

 very hardy and will live in an aquarium all winter. But they 1 

 are thorough carnivores and must be supplied with small 

 water insects or with worms like Enchytrceida. J 



Dragonflies, Suborder Anisoptera, Family Libellulidae, 

 adults called skimmers. — Xymphs of this family have a mask- 

 like labium which covers the whole front of the face up to the 

 antennae (Fig. 161). 



Fig. 161. — XymphofL/&f//«/G; face view showing 

 the labium covering the face. (From Kellogg.) 



Tenspots, Libellula. — Xymphs of Lihellula distinguish- 

 able by their squarish heads and flaring labia are common in 

 vegetation-filled ponds and ditches. (PI. X.) When fullgrown 

 they are nearly two inches long. 



216 



