DIPTERA. | chs 
When first found, in early March, they are quite small, but they grow rapidly dur- 
ing the latter part of March and early April. They are quite stationary when not 
disturbed. Besides being fastened to the leaf by the last posterior segment, they 
are also securely anchored by a very fine silken thread. When disturbed they loosen 
their hold at once and float down stream, suspended and retarded by this thread, 
which very rapidly increases in length while the larve are drifting with the current. 
While thus drifting they jerk about in a lively manner, searching for a new resting 
place, and sink to the bottom quite gradually. Owing to their small size and to 
the fact already stated, that their color is in harmony with their surroundings, or 
with the leaf upon which they are fastened, these larve are difficult to detect in a 
depth of 3 to 4 inches. When removed and put ina glass vessel they soon settle 
against the sides of their prison and can then be studied with a lens. 
- The larva can move about very rapidly in the manner of a span-worm, but with 
this difference, that it always remains anchored by means of a thread, which length- 
ens as the animal proceeds. Being very restless 
and active in such confinement, it will keep on 
looping for hours, at a rate of twenty to twenty- 
five loops per minute. It can move both forward 
and backward, the forward motion being pro- 
duced by fastening the single thoracic leg to the 
side or bottom of the vessel, loosening the anal 
proleg, bringing it close to the former, and let- 
ting the latter go at almost the same moment, the 
backward motion being simply a reversal. In 
the course of six to eight hours the larva becomes 
weak and sickly. It will drop to the bottom of 
the vessel if disturbed, but will no longer try to 
escape. All the larve thus imprisoned, in re- 
peated trials, died in the course of twenty-four 
hours. A colony of nearly full-grown larve, in a 
small creek, shared the same fate when the over- 
flow of the Mississippi River created a back flow Fig. 17.—Simulium meridionale: a, co- 
and made the water in this creek stationary for coon; b, pupa—enlarged (from Riley). 
some time. 
All the creeks and branches in which such larve were found by Mr. Lugger 
descend in beds composed of clay. The Rocky Bottom Branch, a tributary to the 
Horn Lake Creek, Mississippi, has worn out a bed in a solid deposit of stratified 
ferruginous sandstone, intermixed with conglomerations of the same substance. 
The water, 6 to 8 inches deep in normal seasons, even during the summer months, 
runs over this stony bed in very rapid currents, forming everywhere little cascades, 
and no better breeding places for the larvie of any Simulium could be imagined. 
Yet none could be found, plainly indicating that the species under consideration 
must be able to fasten to submerged material to find a suitable home. 
The larve form their cocoons just above the bottom of the smaller 
perennial streams and are hence not endangered by the variations in 
the depth of the water, for while it may rise suddenly with every heavy 
rain and fall as suddenly afterwards the depth is quite uniform at other 
times. 
The cocoon (fig. 17, a) is much neater than that of S. pecuarum, being 
formed of fine threads, lined with gelatinous ones. The web is quite 
dense, uniform, with well-defined, sometimes thickened rims. The 
cocoon is always securely fastened singly to a leaf or stick, and even if 
many are fastened upon the same leaf they do not crowd each other. 
