AQUATIC INSECTS 905 



the plant. The adult beetles spend their lives among the leaves 

 of the plants, flying actively about when disturbed. They are of 

 shining, metaUic coloration, blue or green. Those that Uve on water 

 lilies deposit their eggs through holes eaten in the leaves, arranging 

 them in a curve around the opening on the under side. They are able 

 to place them thus through the possession of a long extensile 

 ovipositor. 



The family Hydrophilidae is in part terrestrial and in part aquatic, 

 and the aquatic members show all degrees of adaptation to water 

 life. A few of the larger forms are expert swimmers, but many of 

 the smaller ones are fitted only for dabbling around in the mud at 

 the water's edge. The best-known member of the family is perhaps 

 the big black Hydrophilus, with finely fringed swimming legs and 

 with keeled sternum. It is attracted to electric lights in vast 

 numbers in the spring, where it falls beneath them and flounders 

 around in the dust of the street, giving a fine illustration of the use- 

 lessness of its specialization when in an unsuitable environment. 

 The larva of this beetle is commonly taken in ponds, not swimming, 

 but clinging to stems at the surface, its squat, hairy body not well 

 fitted for getting through the water, but with immense rapacious 

 jaws, very capable of seizing large Mayfly nymphs and adult Eu- 

 hranchipus when these swim within reach. Another hydrophilid 

 which often swarms into trap lanterns set over streams is Berosus, 

 whose aquatic larva is provided with lateral paired abdominal ap- 

 pendages somewhat like those of the neuropterous genus Sialis. 



The eggs of Hydrophilus are laid in a white membranous capsule 

 attached to plant stems and leaves at the surface of the water. 



The Amphizoidae and Parnidae are found as adult beetles clinging 

 to logs and stones in clear flowing streams. The former family 

 contains but a few far western species; the latter is widely dis- 

 tributed, and contains numerous genera and species. The name 

 ''Riffle beetles" is applied to them to indicate the seat of their 

 greatest abundance. They are mostly of small size and their 

 coloration is usually inconspicuous, although some of them are 

 striped with red or yellow. The adults sun themselves on the 

 stones that protrude from the water, and fly readily from one rest- 

 ing place to another. Many of the larvae, especially the larger 



