282 



INTRODUCTION TO ZOOLOGY 



CHAP. 



All the four genera of Heteroptera so far mentioned have 

 been alike in living a submerged life, and in having small 

 and concealed antennae. Those now to be described {Hydro- 

 metra, Gerris, and Velio) all have long and conspicuous 

 antennae, and they live on the surface of the water, running 

 or jumping actively over the surface film, though occasionally 

 penetrating it to dive below. 



Series B. Forms living on the surface of the water and having 

 conspicuous long antennae. 



The Pond-skater (Gerris). 



The little narrow -bodied, long-legged Pond-skaters are 

 very numerous on the water surface, over which they slide, 

 or sometimes progress in a series of 

 leaps. Occasionally they dive below 

 the surface, when the hairy body 

 is seen to have a silvery air-film 

 covering it. The four-jointed an- 

 tennae are so long as to look almost 

 like an extra pair of legs. The 

 first pair of legs are held forwards 

 and used for prehension. By the 

 lengthening of the first segment of 

 the thorax, this pair is widely 

 separated from the second pair, 

 which is that chiefly used in loco- 

 motion, the hind -pair serving to 

 guide the movements. As in all 

 water-bugs, this genus has a long 

 beak with which the food is pierced 

 and its juices extracted. It feeds 

 very largely on dead and dying 

 insects that fall on to the surface 

 of the water. 



The adult insects are nearly half 

 an inch long, but are not all alike. Some have only short 

 wings, and are incapable of flight, whilst others have well- 

 developed upper horny wings and lower membranous ones 

 with which they can fly. 



Fio. 208.— The Pond-skater 

 ( Gerris). 



Larva above, adult below— winged 

 variety. (Real lengtb shown 

 by the lines to the left.) 



