22 Bulletin No. 159 



The appearance of the adult is often very sudden in a 

 neighborhood, sometimes accompanying a change in the wind. 

 With strong wings it flies rapidly, and thus probably often 

 migrates considerable distances from the waters in which it 

 develops. The gnats attack stock by creeping into the ears 

 and nostrils, and collect over the prominent veins along the 

 under side of the body, when very abundant alighting upon 

 and attacking any part. Riley, who studied the insects many 

 years ago in Mississippi, says that they are most active during 

 dark cloudy weather when a storm is brewing, but that in 

 bright days from eleven o'clock in the morning to four in the 

 afternoon they are inclined to be inactive. 



When first attacked animals suffer greatly, and often 

 become quite frantic. They grow more accustomed to the 

 injury after a time and submit to it without fretting. It is 

 said that the stock in gnat-infested regions become to an 

 extent immune, or at any rate animals learn to take better 

 care of themselves and do not so often succumb as does 

 stock recently brought to the region. 



The puncture seems to be intensely irritating, and brings 

 blood at once. Oddly, the poison causes in animals an 

 ailment resembling colic, a fact which will recall the ac- 

 companying digestive derangements in pellagra. A poison 

 of some sort appears to be injected into the blood, and the 

 result on badly stung animals is said to be somewhat like 

 that following the bite of the rattlesnake. 



Smudges of smoke, and sponging with coal-tar water, 

 fish oil and some other preparations, are used to repel the 

 insects. Many of those tried are ineffective. 



Simulium pictipes ( The Innoxious Sand Fly) . 



t"\g. 7. — Larva of S. picttpes. x lo. 



The larva of a third species of the genus has long been 

 known to me as occurring in great numbers in small streams 



