256 



Beetles 



philidae) (p. 258) by having slender thread-like antennae instead of clubbed 

 ones. All are oval and flatly convex in shape, with .hard smooth body-wall, 

 usually brownish or black, and when at rest hang head downward from 

 the surface of the water, the characteristic breathing attitude. The females 

 sometimes have the elytra furrowed with shallow longitudinal grooves, and the 

 males of most species have a curious clinging-organ on the expanded first three 

 or four tarsal segments of the front feet (Fig. 349). This organ is com- 

 posed of a hundred or more small capsules on short stems and two or three 

 very much larger pads. It is used for holding the females in mating, and" 

 adheres to their smooth body-wall by the secretion of a gummy fluid insol- 

 uble in water. The pads and capsules may also act to some extent as 

 "suckers" by atmospheric pressure. The hind legs are long, strong, 

 and flattened to form oars or swimming-organs. This beetle regularly and 

 perfectly "feathers its oars" by a dexterous twist while swynming. To 

 breathe, the beetle comes to the surface its body being less dense than 

 water, it floats up without effort and projects the tip of its abdomen through 

 the surface film. It now lifts the tips of the elytra slightly; air pours in 

 and is held there by the fine hairs on the back, where are also the spiracles, 

 I or breathing-openings. Thus when the beetle goes down 



again it carries with it a supply of air by means of which 

 respiration can go on for some time under water. The 

 diving beetles can be readily kept in aquaria, as can also 

 their larvae (described in the next paragraph), and the 

 interesting active life with the characteristic swimming, 



diving, breathing, captur- 

 ing of prey, and feeding 

 all easily observed. 



The life-history of 

 no American species has 

 been completely worked 

 out, but the eggs of some 

 species are dropped ir- 

 regularly on the water, 

 while those of others are 

 laid in slits cut by the 

 sharp ovipositor of the 

 female in the Stems of 



aquatic plants. The long, 



slender, semi-transparent, 

 predaceous larvae (Fig. 348) are known as water-tigers. They have six slender 

 legs and the head is large and flattened. It bears long, slender, curved, 

 sharp-pointed, hollow mandibles, each with a small opening at the tip and 



348. FIG. 349. 



FIG. 348. Water-tiger, the larva of the predaceous water- 

 beetle, Dyticus sp. (Natural size.) 



