BLACK-FLIKES. 181 
larger tube that communicates with the interior tracheal 
system. Gradually the fly forms inside the pupa, and when 
ready to issue it leaves its old quarters, and popping to the 
surface like a cork runs over it, and flies off to the shore to 
harden its chitinous covering. Such larve and pupz abound 
in all our northern streams, but only in places where there 
is a swift current. Here the eggs are also deposited, and 
most frequently upon stones near enough to the surface of 
the water to be kept moist, or upon the projecting parts of 
submerged objects. The female is, in fact, able to dive, and 
can deposit her eggs even under water. These eggs are ar- 
ranged in a very neat manner, and are usually white, as 

Fig. 150—Simulium tribulatum. Female. Fig. 151.—Simulium tribulatum. Male. 
Greatly enlarged. Original. Greatly enlarged. Original. 
shown in fig. 146. The adult gnats, that were obtained 
from the larve and pupe illustrated, are shown in figs. 150 
and 151. The male, ascan be seen in fig. 151, varies very 
much from the female, fig. 150, being much smaller and hay- 
ing very large, brilliant red eyes that meet on top of head; 
the markings are also quite different, the body being velvety 
black with bright golden-yellow and blue spots; the female 
is gray with black markings. This species is the most abun- 
dant one, usually called in Minnesota the ‘‘black-fly” though 
quite different from the genuine article. 
Very little can be done to destroy this insect in its earlier 
stages. The removal of obstructions in the rivers, which 
cause an acceleration of the motion of the water, would de- 
