Plancton Gatherers 



365 



The nymph of the "Howdy" Mayfly, Chirotenetes, fixes 

 itself firmly with the stout claws of its middle and hind 

 feet clutching a support, and extends its long fore feet 

 with their paired fringes of long hair outspread like a 

 basket to receive what booty the current may bring. 

 These four are so different they are better considered 

 a little further separately. 



The larva of Simulium (the black-fly, or buffalo gnat) 

 perhaps the most wide-spread and characteristic animal 



SIMULIUM 



HYDMPSYt 



FIG. 217. Plancton-gathering insects 

 of the rapids. The arrow indicates 

 direction of stream-flow. 



of running water, is unique in form and in habits. It 

 hangs on by means of a powerful sucker that is located 

 near the caudal end of its soft and pliant bag-shaped 

 body. But it may also attach itself to the stones by a 

 silken thread spun from its mouth: and if it then 

 loosens its sucker, it will dangle at the end of the thread, 

 head upstream. By means of these two attachments, 

 it may travel from place to place without being washed 

 away, but in the swiftest water, it can make only short 

 moves sidewise. It travels by loopings of its body, like 

 a leech. So it shifts its location with changes of water 

 level, always seeking the most exposed ledges which a 

 thin sheet of water pours over. There it gathers in 

 companies, so closely placed side by side as to form 

 great black patches on the stones. 



