SOME AQUATIC INSECTS 77 



cases do not rest closely against the body, but 

 are slightly arched, so as to leave a cavity 

 between themselves and the insect's body, the 

 cavity so formed acting as a kind of air reservoir. 

 When the Beetle wishes to breathe, it rises to 

 the surface of the pond, and slightly raising the 

 wing-cases, takes in a quantity of air, which is 

 drawn in by the large oval spiracles situated 

 along the back. 



The sexes are easily distinguished in the 

 Dytiscus Beetle by the difference in the structure 

 of the wing-cases, the males having perfectly 

 smooth ones, while those of the female are 

 generally, though not always, grooved. The 

 first pair of legs also differ in the two sexes, 

 those of the male Beetle having the three basal 

 joints of the tarsus flattened and widened, and 

 armed on the under surface with a number of 

 small suckers or cupules, and with a pair of 

 large ones. These suckers are used by the male 

 as clasping organs, enabling him to securely 

 grasp a slippery victim, and also to hold his 

 ladylove in a firm embrace. In the female, the 

 first pair of legs are quite simple and destitute 

 of suckers. The second pair of legs terminate in 

 a pair of well-developed claws, and are used 

 chiefly for walking and climbing, while the third 

 pair are flattened out and fringed with hairs, and 

 serve as oars to propel the Beetle through the 

 water. The second and third pairs of legs are 

 similar in both sexes. 



The Dytiscus Beetle spends most of its life 

 in the water, where it hunts and captures its 

 prey, but in the summer-time it frequently quits 



