BLACK-FLIKES. 177 
June 1, and very likely breeds in the Mississippi river near 
Minneapolis, though the earlier stages have, as yet, not been 
found. | 
A little later in the season, but chiefly during June and 
July, a somewhat larger species (Simulium decorum Walk.) 
becomes numerous. A female is shown in fig. 144. This 
species occurs sometimes in large numbers, but only females 
have been found thus far. This is of course easily explained 
by the fact that only the females of these flies are blood- 
thirsty; the males remain near the place of their birth, some 
running water, and as they have only a rudimentary mouth 

Fig. 145.—Simulium irritatum,n.s. Male. Greatly enlarged. Original. 
they could not imbibe blood, even if they were inclined to do 
so. This fly attacks, by preference, cows, and is sometimes 
found in such large numbers as to cause some injury to 
them. They are found most usually in the ears, and be- 
tween the legs, or wherever the skin of the animal is thin 
and not well covered with hairs. Sometimes the cows suffer 
severely from their attacks, and being constantly irritated 
by these small tormenters they lose in flesh and give less 
milk. As seen in the illustration this fly is rather prettily 
marked. The front feet are in constant motion, a habit all 
species have, and are utilized more as feelers than as legs. 
