BLACK-FLIES. 



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 {SimuUmrh 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. — Simitliumirritaturn, 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. 



