AQUATIC INSECTS 



Plea. — The pigmy water-bugs of this genus (Fig. 182, 2) are 

 not more than a fifth of an inch long. They live in tangles 

 of water plants feeding upon minute crustaceans. 



Water boatmen, Family Corixidae. — Water boatmen (Fig. 

 183) are dark grayish or thickly mottled gray and black. 

 Their hind legs are flattened for swimming and extend out 

 like those of the backswimmers, but water boatmen always 

 swim with their backs up; their middle legs are long and end 

 in very slender claws. The boatmen dive down with their 

 bodies wrapped in a glistening blanket of air and being so 

 much lighter than the water they have to anchor in order to 

 stay below. They do this by almost imperceptibly catching 

 one claw of the middle leg into some plant stem (Fig. 183) 

 and hang there atilt in the water for long intervals. Indeed 

 they spend a good part of their time on the bottom for they 

 feed upon the soft vegetable ooze which gathers there, diatoms, 

 desmids, filamentous algae, and the like (PI. IV). Hunger- 

 ford discovered that water boatmen are vegetarians, thus 

 disproving the old statement that all aquatic Hemiptera are 

 predacious. He found Spirogyra filaments v/ith their cells 

 sucked so empty by boatmen that only their walls remained. 

 They are orobably omnivorous since Hale in Australia ob- 

 served them feeding on mosquito larvae. 



It is difficult to distinguish one species of water boatmen 

 from another, and even the genera are hard to differentiate. 

 One of the commonest species is here figured; many are similar 

 to it. 



Water boatman, Arctocorixa (Corixa) altemata. — Like 

 others of the family this water boatman is active all winter. 

 Large numbers of corixids have been taken every month of 

 the year from a gently flowing stream near South Hadley, 

 Massachusetts. In midwinter they hide under the banks 

 in tangled masses of Chara where they are far from inactive 

 (Fig. 183). In Ithaca, N. Y., on May 9 Hungerford found 

 red water-mites (p. 175) on about eighty five percent of 



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