Simuliidce, or Black Flies 
105 
white slime, which becomes darker, until finally it becomes black just 
before the emerging of the larvae. The egg stage lasts a week. 
The larvae (fig. 75) arc black, soft skinned, somewhat cylindrical 
in shape, enlarged at both ends and attenuated in the middle. The 
posterior half is much stouter than the anterior part and almost club- 
shaped. The head bears two large fan-shaped organs which aid in 
procuring food. Respiration is accomplished by means of three so- 
called blood gills which are pushed out from the dorsal part of the 
rectum. The larvae occur in enormous numbers, in moss-like patches. 
If removed from their natural habitat and placed in quiet water they 
die within three or four hours. Fastened to the rock by means of a 
disk-like sucker at the caudal end of 
the body, they ordinarily assume an 
erect position. They move about on 
the surface of the rocks, to a limited 
extent, with a looping gait similar to 
that of a measuring worm, and a web 
is secreted which prevents their being 
washed away by the swiftly flowing 
water. They feed chiefly upon algas 
and diatoms. 
The complete larval stage during 
the summer months occupies about 
four weeks, varying somewhat with the 
temperature and velocity of the water. 
At the end of this period they spin 76 - simuiium venustum, (x8). 
L j 1 After Garman. 
from cephalic glands, boot-shaped 
silken cocoons within which the} 7 pupate. The cocoon when spun 
is firmly attached to the rock and also to adjacent cocoons. 
Clustered continuously over a large area and sometimes one above 
another, they form a compact, carpet-like covering on the rocks, 
the reddish-brown color of which is easily distinguishable from the 
jet-black appearance of the larvae. The pupal stage lasts about 
three weeks. The adult fly, surrounded by a bubble of air, quickly 
rises to the surface'of the water and escapes. The adults (fig. 76) 
are apparently short lived and thus the entire life cycle, from egg 
to egg is completed in approximately eight weeks. 
In the case of Simuiium pictipes at Ithaca, N. Y., the first brood 
of adults emerges early in May and successive generations are produced 
throughout the summer and early autumn. This species winters in 
