2 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 
sometimes cause the death of live stock. At the present time no cases 
of disease transmission can be attributed definitely to buffalo gnats, 
but there is a possibility that future investigations will show some 
important connection with the transmission of diseases. 
All of these considerations make it advisable to place on record a 
considerable number of observations which will serve as a basis for 
the control of these insects wherever they occur. 
The major part of the biological experiments outlined in this paper 
were carried on at Spartanburg, S. C. The author wishes to ex- 
press his thanks to Mr. A. H. Jennings, under whose direction the 
work was done, to the Thompson-McFadden Pellagra Commission 
for many courtesies received, and to the directors of the Spartan- 
burg Hospital for the generous way in which they afforded labora- 
tory accommodations and facilities. 
THE ADULT STAGE. 
DESCRIPTION OF EXTERNAL ANATOMY. 
The adults of the genus Simulium are usually very small, the 
largest known North American species (S. pictipes) not measuring 
more than 4 mm. in length. They are compact in shape, the head 
being decidedly small in proportion to the rest of the body, and the 
thorax greatly developed and curiously humped. In some species 
the thorax and abdomen are very pubescent, in others almost naked. 
In color the different species vary greatly, ranging from brilliant 
iridescent yellow and various shades of gray to almost black. 
The species of Simulium are holoptic in the male and dichoptic in 
the female. In the female the facets of the eyes have an equal grada- 
tion in size, diminishing somewhat toward the margin. In the male 
the facets suddenly decrease in size along a line extending on each 
side from the antennal socket around to the post-gense, giving the 
lower portion of the eye the appearance of being divided off by a 
suture. In color the eyes are usually iridescent bronze in the female 
and deep iridescent red in the male. Ocelli are wanting in both sexes. 
The antennas are short, moniliform, and 11-segmentecl. In the 
species here dealt with the antennas of the female have the first seg- 
ment short and cup-shaped. The second is longer, the apical end 
bearing a chitinous ring which serves as the point of attachment for 
the third segment, which is nearly the same in length as the second, 
but pedicellate. The remaining segments are nonpedicellate, broadly 
joined. Segments 4, 5, 6, 7, 8, and 9 are subequal. The tenth seg- 
ment is slightly longer. The eleventh is the longest of the entire 
antenna, narrows to a point at the apical end, and bears from two to 
three short, strong bristles. The first two segments are minutely 
pubescent, with a few strong bristles on the apical portion; the re- 
