LIFE IN PONDS AND STREAMS 



firmly braced, it holds its hairy front legs close beneath its 

 bewhiskered mouth-parts and stands ready for whatever 

 food the water may bring to it. 



Attached to the rocks by a sucker on the hind end of the 

 body, larvae of the black fly Simulium (Fig. 233) swing out 

 into the water, spreading their fan-shaped food-brushes to 

 sweep the diatoms and floating algae into their mouths. If 

 its end sucker loses hold the larva is washed downstream; 

 but even then if it can only get its mouth in contact with 

 a stone or stick it will use some of its silk-like saliva to tie 

 itself down again, swinging upon this till it can once more 

 anchor its sucker. 



Fig. 25. — Epeorus, a mayfly of the rapids, and its 

 mouth parts showing their diatom rakes: i, nymph; 

 2, right and left upper jaws or mandibles; 3, right 

 and left lower jaws or maxillae; 4, tongue; 5, lower lip 

 or labium. 



Planarians, snails, and most of the mayflies suck or rake 

 and scrape the green algal slime from the stones and like 

 sheep in a pasture they can get their mouths close down to 

 the smallest growths. The planarian actually swings its 

 sucking proboscis out from the center of its body (Fig. 93) ; 

 but the mouths of mayflies are beneath their flattened heads 

 and are similarly effective (Fig. 25). Mayflies of the rapids 

 like Heptagenia, Epeorus and Iron, have horny teeth and 



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