THE FARM STREAM 37 



thread is exuded at the mouth (as a 

 liquid which hardens on contact with the 

 water), attached to the stone and spun 

 out to the desired length. The larva, with thfbUdJ-fly ^lifSmf. 

 disc loosened, swings free upon the thread, 

 reversed in position and hanging with head upstream. 

 After a time it will fasten itself by its sucker again. By 

 using a very short thread and its sucker alternately, the 

 larva may move short distances over the supporting surface 

 in a series of loopings, its position being reversed at each 

 attachment in a new place. Black-fly larvae are excellent 

 food for fishes, but they live for the most part in places that 

 are to fishes wholly inaccessible. They feed upon micro- 

 scopic organisms and refuse adrift in the stream, and they 

 gather their food out of the passing current by means of a pair 

 of fan-like strainers, located on the front of the head near the 

 mouth. Adult black-flies of certain species bite fiercely in 

 northern forests. Other species, known as "buffalo-gnats" 

 and "turkey-gnats", are important pests of live stock. Other 

 species are harmless. 



In the same situations with the 

 black-fly larvae, the neat little food- 

 traps of the seine-making caddis-worms 

 may always be found. Each is a little, 

 transparent, funnel-shaped net, half an 

 Pig. is. Diagram of a. inch wide, opening always upstream, 

 fisSnTappar'Suf and™ s and tapering downward into a silken 

 SSonZhe'?S tube, lodged in some sheltering crevice, 

 taSfof^diitenled in which the greenish, gill-bearing 

 wtlr^stfai^d-l, the caddis-worm that makes it dwells. 

 £»a5to£»M£ Then there is a group of diverse in- 

 doJ^fthet&Lwhich sect larvae found habitually in the 

 Iti^otti^AlUtl rapids clinging to stones, that agree 

 MinSoeA. e NoyeS! ngby in being flattened and more or less 



