THE FARM STREAM 37 
Fic. 17. The larva of 
the black-fly (Simulium). 
thread is exuded at the mouth (as a 
liquid which hardens on contact with the 
water), attached to the stone and spun 
out tothe desired length. Thelarva, 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 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 livestock. 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 
Fic. 18, Diagram of a 
seine-making caddis-wocm's 
fishing apparatus and his 
dwelling; arrows indicate 
the direction of the current 
over the stream bed; a, the 
front edge of the distended 
seine through which the 
water is strained; }, the 
catching surface of finer 
mesh at the bottom of the 
seine and adjacent to the 
door of the tube, ¢, in which 
the larva dwells, in the 
shelter of the rock, d. (After 
an unpublished drawing by 
Miss ‘Alice A. Noyes). 
inch wide, opening always upstream, 
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 
