i66 



ENTOMOLOGY 



Ranatra, likewise have prehensile front legs along with powerful piercinj 

 organs. The electric light bugs, Belostoma and Benacus (Fig. 23) evei 

 kill small fishes by their poisonous punctures. Some other kinds, as the 

 water-skaters (Gerridae, Fig. 228), depend on dead or disabled insect 

 The species of Hydrophilus (Fig. 229) are to some extent carnivorous 



FIG. 227. Backswimmer, Notonecta insu- 

 lata, natural size. 



PIG. 228. Water-skater, Gerris remigis, 

 natural size. 



larvae but phytophagous as imagines, while Dytiscidae (diving beetles) 

 are carnivorous throughout life. Aquatic insects eat not only other 

 insects, but also worms, crustaceans, mollusks or any other available 

 animal matter. 



Even aquatic insects are not exempt from the attacks of parasitic 

 species. A few Hymenoptera actually enter the water to find their 

 victims, for example, the ichneumon Agriotypus, 

 which lays its eggs on the larvae of caddis flies. 



Locomotion. Excellent adaptations for 

 aquatic locomotion are found in the common 

 Hydrophilus triangularis (Fig. 229). Its general 

 form reminds one of a boat, and its long legs 

 resemble oars. The smoothly elliptical contour 

 and the polished surface serve to lessen resistance. 

 Owing to the form of the body (Fig. 230, A) and 

 the presence of a dorsal air-chamber under the 

 elytra, the back of the insect tends to remain 

 uppermost, while in the backswimmer, Notonecta 

 (Fig. 230, B), on the other hand, the conditions 

 are reversed, and the insect swims with its back 

 downward. The legs of Hydrophilus , excepting the 

 first pair, are broad and thin (Fig. 231, A) and the tarsi are fringed with 

 long hairs. When swimming, the " stroke" is made by the flat surface, 

 aided by the spreading hairs; but on the " recover," the leg is turned so 



FIG. 229. Hydroph- 

 ilus triangularis, nat- 

 ural size. 



