482 AN INTRODUCTION TO ENTOMOLOGY 



by two species in California, the prothorax is quadrate ; in the other 

 genera it is narrowed in front. In Haliplus the last segment of the 

 palpi is small and awl-shaped; in Peltodytes it is longer than the 

 third segment, and conical. The last two genera are widely distribu- 

 ted. 



Family DYTISCID^ 



The Predacious 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 predacious 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 appearance, by the thread-lilce form of the antennas. 

 The hind legs are the longest and are fitted for swimming, being 

 flattened and fringed with hair. The middle and the hind pair 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 di- 

 lated and form a circular disk, upon 

 the under side of which are little cup- 

 like suckers (Fig. 566); these serve as 

 clasping organs. In a few cases the 

 middle tarsi are dilated also. The fe- 

 males of some species exhibit an inter- 

 Fig. 566. Fig. 567. esting dimorphism in that some 



of the individuals have the elytra fur- 

 nished with a nimiber of deep furrows (Fig 567), while others of the 

 same species have them smooth. 



The diving-beetles abound in our streams and ponds, but they 

 are more often fotmd in standing water than in streams. When at 

 rest they float in an inclined position, head downward, 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 the air 

 becomes impure the beetle rises to the surface, forces it out, and 

 takes a fresh supply. 



These beetles are very voracious. They destroy not only other 

 insects, but some of them will attack larger animals, as small fish. 

 When kept in aquaria they can be fed upon any kind of meat, raw 

 or cooked. They fly from pond to pond, and are often attracted to 

 light at night. Many of the species make sounds, both under the 

 water and in the air. In some cases this is done by rubbing the 

 abdominal segments upon the elytra ; in others, by rubbing the hind 

 legs upon a rough spot on the lower side of the abdomen. 



