FIELD BOOK OF PONDS AND STREAMS 



Adults and pupce of water-beetles breathe air and most of 

 their larvae do likewise. Some of the most interesting 

 habits and structures of these larvae are those by which they 

 remain in the water and still contrive to have access to air. 

 Only a few of them have tracheal gills which enable them to 

 breathe under water; the family Gyrinidce, whirligigs (p. 271), 

 and a few of the Hydrophilidce (p. 273), have filamentous gills 

 along the sides of the abdomen; DryopidcE and the Psepheni- 

 dcB or water pennies (PI. VIII) have fringed gills beneath the 

 body. 



Some beetles are familiar to everybody although under 

 names which disguise their identity, potato "bugs," rose 

 "bugs," fire "flies," and maybeetles commonly called June 

 "bugs." • 



If a diving beetle like Dytiscus be compared with any of 

 them its adjustments to water life will be very apparent. 

 An adult Dytiscus (Fig. 209, i) has a compact, rigid, slippery 

 body, its head forming the point of a wedge and the smooth 

 sides of the body the rest of it. The underside is boat- 

 shaped, and the hind legs bladed like oars. Between strokes 

 it folds its legs close against the body, and pulls its antennae 

 down so that there are no outriggers to resist the water. It 

 carries a reservoir of air lightly shut in between its wing 

 covers and the body; its air-tubes or tracheae open into this 

 reservoir making it available for breathing. Water-beetles 

 carry their air supply in different ways and use it for support 

 as well as for breathing. The underside of the body of a 

 whirligig beetle is covered with short hairs which catch a 

 film of air, buoying it up on the surface, but none of it is acces- 

 sible for breathing. The hydrophilids and the water striders 

 of the Hemiptera have similar air-floats, which appear to 

 lighten their body weight as swim-bladders do for fishes or 

 air-sacs for honey-bees. 



Habitat, season. — Nearly all aquatic beetles live in quiet 

 water thickly grown with plants on which they hunt for their 



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