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 

 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 surf ace 

 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, 

 f to and tapering downward into a silken 

 tube, lodged in some sheltering crevice, 

 in which the greenish, gill-bearing 

 caddis-worm that makes it dwells. 



Then there is a group of diverse in- 

 sect larvae found habitually in the 

 rapids clinging to stones, that agree 

 in being flattened and more or less 



