POND INSECTS 69 



top of the aquarium, for the water-striders can leap several inches, 

 and might thus escape. 



Observe th^ character and disposition of the different pairs 

 of legs of the water-striders. Note their use in running and 

 grasping their prey. Are the legs of the water-strider thrust into 

 the water ? No, they rest on top of the water, the whole weight 

 of the insect being supported by the tense surface film ( see the 

 lesson on the mosquito). Note the "dimples" or depressions in 

 this film where the feet press it down. Are the water-striders 

 winged or wingless ? They may be, strangely enough, either 

 winged or wingless; that is, there are two kinds of individuals of 

 water-striders. In addition to the elongate narrow-bodied forms 

 you may see some individuals with shorter, broader bodies, either 

 entirely without wings or with short wing-pads or growing wings. 

 These are simply the young or immature water-striders. Exam- 

 ine one of the insects closely, using, if necesssary, the magnifier. 

 Note the slender, sharp-pointed, little beak which projects from the 

 head. Note the black bead-like eyes. The under side of the body 

 is covered with a fine pile or pubescence. If you hold the water- 

 strider in the water (underneath the surface) the underside of the 

 body will be silvery white, showing that a film of air is held en- 

 tangled in the pubescence, and preventing the 

 wetting of the body. When you let loose of the 

 insect it will rise immediately to the surface, and 

 run abotit as usual, having not been wetted by its 

 submersion in the water. 



The whirligig beetles (fig. 42) are, like the 



. Fig. 43. Whiri- 



water-stnders, suriace msect^; they are to be -igig-beetie (g> 



• 1 1 rintis). 



found m the same places with the water-stnders. 

 These whirligig beetles are small (usually about one-third of 

 an inch long), oval or elliptical, flattened, shining black 

 insects, which dart swiftly about in curving paths on the water. 

 They may readily be kept in the school-room aquarium. Do they 



