io6 Parasitic Arthropoda 



the larval condition. Most of the other species of Simulium which 

 have been studied seem to be single brooded. 



While Simulium pictipes does not attack man, there are a number 

 of the species which are blood-sucking and in some regions they are a 

 veritable scourge. In recent years the greatest interest in the group 

 has been aroused by Sambon's hypothesis that they transmit pellagra 

 from man to man. This has not been established, and, indeed, seems 

 very doubtful, but the importance of these insects as pests and the 

 possibility that they may carry disease make it urgent that detailed 

 life-histories of the hominoxious species be worked out. 



As pests a vivid account of their attacks is in Agassiz's "Lake 

 Superior" (p. 6i), quoted by Forbes (1912). 



"Neither the love of the picturesque, however, nor the interests of 

 science, cotild tempt us into the woods, so terrible were the black flies. 

 This pest of flies which all the way hither had confined our ramblings 

 on shore pretty closely to the rocks and the beach, and had been 

 growing constantly worse, here reached its climax. Although de- 

 tained nearly two days, * * * we could only sit with folded 

 hands, or employ ourselves in arranging specimens, and such other 

 operations as could be pursued in camp, and under the protection of 

 a 'sn>udge.' One, whom scientific ardor tempted a little way up the 

 river in a canoe, after water plants, came back a frightful spectacle, 

 with blood-red rings round his eyes, his face bloody, and covered with 

 punctures. The next morning his head and neck were swollen as if 

 from an attack of erysipelas." 



There are even well authenticated accotints on record of death of 

 humans from the attacks of large swarms of these gnats. In some 

 regions, and especially in the Mississippi Valley in this country, cer- 

 tain species of black flies have been the cause of enormous losses to 

 fanners and stockmen, through their attacks on poultry and domestic 

 animals. C. V. Riley states that in 1874 the loss occasioned in one 

 county in Tennessee was estimated at $500,000. 



The measures of prevention and protection against these insects 

 have been well summarized by Forbes ( 1 9 1 2) . They are of two kinds : 

 "the use of repellents intended to drive away the winged flies, and 

 measures for the local destruction of the aquatic larvs. The repel- 

 lents used are either smudges, or surface applications made to keep 

 the flies from biting. The black-fly will not endure a dense smoke, 

 and the well-known mosquito smudge seems to be ordinarily sufficient 

 for the protection of man. In the South, leather, cloth, and other 



