THE INSECT WORLD. 



169 



Fig 



mandibles, and a pair of bristly processes at the anal end of the 

 body. 



Two other families belonging to the Adephaga are aquatic in 

 the larval as well as adult stage, and are as predaceous as their 

 terrestrial relatives. 

 The DytiscidcB and 

 their larvae have been 

 termed 'Svater- 

 tigers," and the larger 

 species attack small 

 fish as well as insects. 

 In form they are oval 

 and somewhat flat- 

 tened, and they may 

 often be seen rising to 

 the surface of quiet 

 pools or spring-holes, 

 head down, releasing 

 a bubble of air, and 

 then, after remaining 

 for a little time, with 

 the anal extremity 

 above the surface, 

 again starting for the 

 bottom. There is con- 

 siderable space between the wing-covers and the abdomen in 

 these species, and this is utilized as a reservoir for the air which 

 the insect breathes beneath the surface. When it becomes impure 

 the beetle rises again to the surface, releases the vitiated air, and 

 takes in a new supply. 



This ends the series Adephaga^ and no practically injurious 

 forms exist in it ; all are more or less beneficial by reason of their 

 predaceous habits. Under some circumstances a few of the 

 species eat pollen, and after midsummer some have been found 

 gnawing grass-seed ; one or two species have even been found 

 eating into the kernels of corn, so there appears to be a tendency 

 to vary to a vegetable diet under certain conditions. In fact it 

 has been demonstrated that in many species some vegetable 

 matter is regularly eaten ; yet, as this feeding is not of a character 



A water-tiger, Dytiscus marginalis.—a, larva, devour- 

 ing an Agrion larva ; b, pupa ; c, male beetle, the elytra 

 of the female at side ; d, anterior tarsus of the male, yviib. 

 sucking disks ; e, tarsus of the female : a, b, c, about 

 natural size. 



