Article beginning on page 106.
Psyche 6:106-107, 1891.

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PSYCHE.
[July 1891.
BY C. H. TYLER TOWNSEND, LAS CRUCES, N. M. In the southern part of New Mexico,
along the valley of the Rio Grande,
there begins to appear about the first of May a buffalo gnat which is quite as
troublesome, especially to man, as its
more eastern congener, S. $ecuurum.
It proves to be an undescribed species.
The first individuals that I have noticed this year were in an orchard near Me-
silla 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 same date but in less numbers
on the college grounds, which are situ-
ated about four 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 on the
amount of snow in the foot-hills to the
north particularly in Colorado, and on
rains, which are only exceptionally a fac - tor. The snow in the canons 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 no doubt is dependent
on the rise of the Rio Grande for its
appearance. Doubtless, also, it is dis-
tributed through the valley by the
system 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 ques-
tion of riparian irrigation on injurious 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 that 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 Mts., and may be met with
also on the elevated mesa nearer the
mountains, especially to the north. On
May 17th I observed them on the sum-
mit of the first mountain at the eastern end of the Dona Ana range, which is
nearer the river than the Organs, and
farther north. The elevation is at least 4,500 (probably 5,000) fL above sea
level, or about 1,500 (perhaps 2,000)
ft. above the level of the river. They
are not found in the Organ Mts., whfch
are about twenty miles east of the river, nor on the plains to the east and south
of them, thougli on the mesa to the




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west they approach to within a few
miles. This was observed May 23d-
24tl1, 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 in-
sect that we have in this locality. Many persons are so susceptible to them as to preserve through the height of the gnat
season a chronic inflammation of the ex- posed parts of the face and neck resulting from repeated bites, which cause an in-
tense irritation and even give rise to
cutaneous sores. The inclination of the
gnats to bite increases with the advance of the season, but the pest is consid-
erably abated after the fall of the
water. They are also very trouble-
some to animals, and are supposed
to cauce the inflamed eyes in the
horses of this region through the sum-
mer months. I append a description
of the species.
The female alone is de-
scribed, as that is the only sex which
composes the biting swarms, and I have
not secured either the male or the early stages.
Si7nzilium occidentale, n. sp. 9. Cinereous, abdomen light fulvous. Head cinereous, eyes black ; face cinereous, raised, somewhat darker in the centre, sparsely clothed with fine sil- very hairs ; front cinereous, widened below into a cross-bar, a prong invading the orbital area on each side, silvery pubescent on the orbital margin, and with longer pubescence on the occipital margin ; proboscis black, brownish at tip, palpi black; antennae cinere- ous, with short, silvery pubescence, the two basal joints longer than the following joints, which are nearly equal in length; occiput cinereous, with silvery pubescence around the margin. Thorax cinereous, mesoscututn en- tirely covered with silvery pubescence, with two dorsal lines, and usually a fainter median line between them; pleurae fulvous posteri- orly; scutellum black, silvery pubescent. Abdomen light fulvous, sparsely covered
with short silvery pubescence; second, third and fourth segments above with a brown
cross-band shading to darker on the sides and in the middle, particularly on the third and fourth segments ; remaining segments with a broad, median, dorsal, cinereous band, bounded laterally on the fifth, sixth and seventh segments by a curved, more or less faint line of brown; venter light fulvous, silvery pubescent. Legs black, silvery pub- escent. Wings hyaline, iridescent by re- flected lights; halteres white. Length of body 2 mm ; of wing 2 mm.
Described from many fresh specimens.
This species is smaller than either
27. i>ecuarum or 6'. meridionale. S.
me/a/Zicum Bell. from Mexico is given
as 2 mm. long, but it is the male which
is described, and the female would be
very much larger. S. occiden/uZe dif-
fers from 5'. pecuarum very markedly
in the thoracic and abdominal markings.
These markings are very much like
those of 5'. meridionale; but the
median thoracic line is always very
faint, the abdomen is light fulvous, the lateral lines of segments 5, 6 and 7 are curved, and the abdominal markings
are of a different color,
besides other
minor differences.




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