FIELD BOOK OF PONDS AND STREAMS 



In one of the largest of these water striders, Rliagovelia obesa, 

 the terminal tarsus of the middle leg has a split in it from 

 which a tuft of hairs projects into the water (Fig. 172), These 

 can be spread out like a fan and used as an oar-blade in 

 travelling up the current of a stream. Length of adult, 

 one eighth of an inch. 



Water striders, Family Gerridae. — Water striders or water 

 skaters live on the surface of quiet or gently JElowing water, 

 skimming rapidly over the surface on their spider-like legs, 

 drifting with the current or jerking themselves upstream 

 (Fig. 22). The dimples which their feet make in the 

 surface film cast shadows on the brook bed that are almost 

 as often noticed as the water striders themselves. Water 

 striders collect in schools along the quiet, shady, side waters 

 of streams from whence they scatter to shelter when alarmed 

 but quickly congregate again. 



Their bodies have pilose surfaces, like velvet, which hold a 

 silvery film of air covering their undersides and completely en- 

 veloping them in their occasional plunges down into the water. 

 Their legs are slender, often long and spindling; the middle 

 and hind ones are close together, both pairs set far apart from 

 the front legs ; the long fem.ora of the hind legs extend behind 

 the tip of the body (Fig. 173). Very young nymphs are like 

 frisky little spiders, but they soon begin to look like the 

 adults except that they have short wings or none at all. 

 In several species adults, too, may be wingless or short- 

 winged. 



Water striders are predacious on backs wimmers, on emerg- 

 ing midges which come up from the water below them, and 

 on leaf-hoppers which fall down from banks and overhang- 

 ing shrubbery above them. The adults pass the winter 

 beneath protecting mud-banks, often clustered among snarls 

 of CJiara and Elodea stems. 



Like some other water-bugs they support many young 

 water-mites. Scarlet patches of the latter can be seen almost 



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