COLEOPTERA. 



523 



Family DYTISCID^E (Dy-tis'ci-dae). 



The Predaceous Diving-beetles 



If one will approach quietly a pool of standing water, 

 there may be seen oval, flattened beetles hanging head 

 downward, with the tip of the abdomen at the surface of 

 the water. Such beetles belong to this family. 



The predaceous diving -beetles are usually brownish 

 black and shining, but are often marked indefinitely with 

 dull yellow. They can be distinguished from the water 

 scavenger-beetles, which they resemble in general appear- 

 ance, by the thread-like form of the antennae. The hind 

 legs are the longest, and are fitted for swimming, being flat- 

 tened, and fringed with hair. The middle and the hind pairs 

 of legs are widely separated. This is due to the very large 

 hind coxae which cover the greater part of the lower surface 

 of the thorax. In the males of certain 

 genera the first three segments of the fore 

 tarsi are dilated and form a circular disk, 

 upon the under side of which are little 

 cup -like suckers (Fig. 630). In a few 

 cases the middle tarsi are dilated also. 

 The females of some species exhibit an 

 interesting dimorphism in that some of the individuals have 

 the elytra furnished with a number of deep furrows (Fig. 

 631), while others of the same species have them 

 smooth. 



The diving- beetles abound in our streams 

 and ponds, but they are more often found in 

 standing water than in streams. When at rest 

 they float in an inclined position, head down- 

 Fic 631. W ard, with the tip of the hind end of the body 

 projecting from the water. The spiracles open on the 

 dorsal side of the abdomen beneath the elytra. By lifting 

 the elytra slightly a reservoir is formed for air, which the 

 beetle can breathe as it swims through the water. When 



Fig. 630. 



