FIELD BOOK OF PONDS AND STREAMS 



over them and mingled; and there was soon but one sur- 

 vivor. Dragonfly nymphs devour many beetle larvae; Anax 

 nymphs (p. 219) take a daily toll of them. 



In the stomach of a painted turtle (PI. XXIII), a little 

 over two inches long, Baker found that the wing covers of 

 beetles formed five per cent of the food mass, and in another 

 only about an inch long, the remains of beetles composed 

 forty per cent. Water birds harvest the beetle crop con- 

 tinually and ducks consume the adults by hundreds. 



Aquarium study. — Both adults and larvas thrive in aquaria 

 and many of their swimming and breathing habits can be 

 best observed there. Like other animals in captivity they 

 are apt to change their food habits ; those which are herbivor- 

 ous may become predacious. Larvas will clamber out of 

 aquaria and adults will fly up from them as they do not do 

 from the ponds. If the water is well oxygenated and they 

 are given enough living prey they can be kept in aquaria the 

 year round. 



Identification. — Kej-s to families of beetles here mentioned, 

 from Needham and Needham (Bibliography, p. 416), slightly 

 modified. 



The Chrysomelidae (except one genus, Donacia), a family 

 of terrestrial beetles later mentioned (p. 278), are not in- 

 cluded in these keys. 



Families of Adult Water Beetles 



1. Hind leg shorter than the fore leg; eyes divided (whirli- 



gigs). Whirligigs, GyrinidcB, p. 271 



Hind leg longer than the fore leg; eyes simple. 2 



2. Base of hind legs covered by coxal plates (creeping 



water-beetles) . 



Crawling water-beetles, HaliplidcE, p. 265 

 Base of hind leg exposed. 3 



3. Antennae shorter than the palpi (scavengers). 



Water scavengers, HydrophilidcB, p. 273 

 Antennae longer than the palpi. 4 



264 



