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. 61), quoted by Forbes (1912). 
“Neither the love of the picturesque, however, nor the interests of 
science, could 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 ‘smudge.’ 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 accounts 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 
farmers 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 (1912). They arc of two kinds: 
“the use of repellents intended to drive away the winged flies, and 
measures for the local destruction of the aquatic larvae. The repel¬ 
lents used arc 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 
