DIPTERA. . 55 
any high water if the obstructions in these creeks were removed, and with the 
sticks and leaves many, if not most of the larve, would be carried away either into 
the main rivers or the lower level of the creeks or lakes where there is no current and 
where they would perish. 
THE WESTERN BUFFALO GNAT. 
(Simulium occidentale Townsend. ) 
This buffalo-gnat is first recorded by Mr. C. H. T. Townsend, in 1891 
(Psyche, Vol. VI, p. 106), from southern New Mexico. 
While no subsequent records have appeared, there is little doubt 
that it has continued to appear along the river valley where it was first 
observed. I can do no better than to quote from Mr. Townsend with 
regard to its habits, ete.: 
In the southern part of New Mexico, along the valley of the Rio Grande, there 
begins to appear about the Ist of May a buffalo-gnat which is quite as troublesome, 
especially to man, as its more Eastern congener, S. pecuarum. It proves to be an 
undescribed species. The first individuals that I have noticed this year were in an 
orchard near Mesilla, on the 7th of May, and they were at that date swarming in 
considerable numbers. Mesilla is about a mile from the Rio Grande, which flows to 
the west of the town. Gnats were found also on the same date, but in less numbers, 
on the college grounds, which are situated about 4 miles from the river. The river 
rises in May, overflows all the low areas lying adjacent to it, and becomes a roaring, 
rushing body of water. Its volume is dependent upon the amount of snow in the 
foothills to the north, particularly in Colorado, and on the rains, which are only 
exceptionally a factor. The snow in the canyons exerts little influence, for its thaw 
is so gradual as not to be felt. I give these data for what bearing they may have 
on the breeding habits of this species. It is well known that Simulium breeds in 
running water, and our species is no doubt dependent on the rise of the Kio Grande 
for its appearance. Doubtless, also, it is distributed through the valley by the sys- 
tem of acequias or irrigation ditches in use in this country, which open from the 
river on a higher level to the north, and furnish the only source of water supply for 
the raising of crops. This is an adverse bearing of the riparian irrigation on inju- 
rious insects. The securing of artesian water and shutting off of the river water 
would no doubt lessen the dispersion of the gnats through the valley. 
From the first part of May the gnats increase in numbers, until by the middle or 
last of the month they are very abundant in all parts of the valley. It is usually 
between this time and the middle of June that the river is at its highest point. 
They are then to be found on the mesa to the east toward the Organ Mountains, and 
may be met with also on the elevated mesa nearer the mountains, especially to the 
north. On May 171 observed them on the summit of the first mountain at the east- 
ern end of the Dojia Ana range, which is nearer the river than the Organs, and 
farther north. The elevation is at least 4,500 (probably 5,000) feet above sea level, 
or about 1,500 (perhaps 2,000) feet above the level of the river. They are not found 
in the Organ Mountains, which are about 20 miles east of the river, nor on the plains 
to the east and south of them, though on the mesa to the west they approach to 
within a few miles. This was observed May 23-24, while in the valley itself at this 
time they were almost unbearable. 
These gnats are a great annoyance to man, by far greater than any other insect 
that we have in this locality. Many persons are so susceptible to them as to pre- 
serve through the height of the gnat season a chronic inflammation of the exposed 
