BUFFALO GNATS OR BLACK FLIES 311 



liar, fan-shaped structures on the head which create currents of 

 water towards the mouth. They may securely anchor themselves 

 by a sucking disk and a tough silken thread. An upright position 

 is maintained in the water, and locomotion is performed after the 

 manner of that of the measuring worms. When full grown the 

 larvae pupate by making small, cradle-like structures on the sides 

 of stones. From these cradles the adults emerge, coming to the 

 surface like corks and running ashore to complete their final 

 hardening. A visit to the north woods hi June and July is rendered 

 extremely disagreeable to most of us on account of their activities. 



FIG. 318. A species of black fly, S. venustrum. Much enlarged. (Lugger.) 



Injury. Black flies at times make life unbearable for both 

 man and beast, in both the North and the South, where running 

 streams are numerous. Man is attacked along the edges of his 

 hair, on his neck, about his eyes, ears, and wrists anywhere 

 where hair is short. These insects readily draw blood and appear 

 to inject a poison, as severe attacks cause marked symptoms of 

 poisoning. As intimated above, they are most active, and their 

 attacks are most severe on warm, sunshiny days. Figure 318 

 illustrates one of the species, Simulium venustwn Say. 



Control. Rubbish should be removed from streams where 

 practicable. Repellent substances may be used upon exposed 



