and their entrance into the eyes, nose, mouth, and
other openings of the body. Their bites appear to be poisonous, and in
seasons especially favorable to the gnats heavy losses of horses and cattle
often occur.

Buffalo gnats are more troublesome in bright, sunny weather than when it is
cloudy, and animals which have not shed their winter coats suffer more from
their attacks than those with smooth coats. Cattle kept in darkened stables
are not molested. The application of one of the fly repellents already
mentioned (p. 502) may help to protect animals from buffalo gnats. The
burning of smudges is also a useful means of protecting stock from the
attacks of these flies.

[Illustration: FIG. 3.--Buffalo gnat. Enlarged. (From Bureau of
Entomology.)]

SCREW WORMS.[15]

Screw worms (fig. 4) are the maggots of a fly (_Chrysomyia macellaria_), so
called from their fancied resemblance to a screw. The adult fly (fig. 5) is
about one-third of an inch long, with a bluish-green body, red eyes, and
with three dark longitudinal stripes on the back (thorax). Attracted by
odors of decay, it deposits its eggs, 300 to 400 at a time, in cuts, sores,
castration wounds, etc. The crushing of a tick on the skin commonly results
in screw-worm infection at that point. The eggs hatch in a few hours and
the larvae or maggots, or so-called screw worms, begin to burrow into the
flesh and continue burrowing and feeding from three to six days, after
which they leave the wound and crawl into the earth, there transforming
into the quiescent pupal stage. This stage is completed in three to
fourteen days. The mature flies then emerge from the pupal envelope and are
soon ready for egg laying. From two to three weeks are therefore required
for the entire life cycle, although under certain conditions it is possible
for the fly to undergo its full development in as short a time as seven
days, and on the other hand as long as a month is often required.

Besides cattle, the screw-worm fly attacks sheep, horses, dogs, and man. In
the case of hogs it is generally the ears which are affected. The fly also
breeds in dead animals, and all carcasses should therefore be buried deeply
or burned. The complete destruction of all dead animals by burning has been
found by the Bureau of Entomology to be by far the best method of
controlling screw worms.

_Treatment for screw worms._--For proper treatment an animal suffering from
screw w