28 
sota fishermen and hunters frequently grease their faces and hands 
with a mixture of kerosene and mutton tallow for the same pur¬ 
pose. Description of measures for the destruction of the larvae and 
pupae in streams may best be left until the life history of the black- 
flies has been discussed. 
General Features of Life History of Illinois Species 
Neither the life histories nor the habits of any of our American 
species have been sufficiently studied, and the one best known 
(S. pictipes, Figs, n, 12, p. 41) happens to be of the least interest 
from our present point of view, since it has never been known to 
bite. Our Illinois species differ considerably in distribution, life 
history, and places of most frequent occurrence. Two of them, the 
so-called turkey-gnat (S. meridionale, Fig. 8, p. 37) and the buffalo- 
gnat (S. pecuarum, Figs. 9, 10, pp. 40, 41) are the species to which 
southern accounts of these insects usually apply. Altho they occur 
occasionally far to the north, they are southern in their general 
range and predominant numbers, and have not been found by 
us in northern Illinois. N. venustum, the black-fly or sand-flv of 
the northern woods, is, on the other hand, perhaps the most abun¬ 
dant species in the north, altho S. vittatum is frequently found in 
its company. The first of these is said by Prof. F. L. Washburn 
to be an annoyance to stock in Minnesota, and the second a tor¬ 
ment to mankind. These two species are the commonest ones in 
northern and central Illinois. We have likewise a fifth species, 
hitherto undescribed, the larva of which is abundant in the Illinois 
River, and four or five others which occur more sparingly in vari¬ 
ous parts of the state. 
Our species differ also in the number of generations, the two 
especially southern forms (pecuarum and meridionale') having, so 
far as known, but one generation in a year, which reaches the 
winged stage in early spring; while the two most abundant north¬ 
ern forms (venustum and vittatum ) appear in the winged stage 
at intervals thruout the summer, and evidently have two or more 
generations-—just how many is not yet known. S. pictipes also 
develops at least two generations. 
Some of these species breed mainly in small streams, while 
others find favorable situations for reproduction in the largest 
rivers. S. meridionale and vittatum are examples of the first 
habit, and pecuarum and venustum of the second. Larvae and 
pupae of all are limited to flowing streams, the larvae quickly dy¬ 
ing, indeed, if transferred to quiet water. They are evidently 
very sensitive to a deficiency of oxygen, and can live, as a rule, 
