The House Fly and How to Suppress It | Page 2

2.--One of the green-bottle flies (_Lucilia caesar_).
Much enlarged.]
In late summer and autumn many specimens of a small fruit fly, known
as the "vinegar fly,"[8] make their appearance, attracted by the odor of
overripe fruit.
All of these species, however, are greatly dwarfed in numbers by the
common house fly. In 1900 the senior author made collections of the
flies in dining rooms in different parts of the country, and found that
the true house fly made up 98.8 per cent of the whole number captured.
The remainder comprised various species, including those mentioned
above.
[Footnote 8: Drosophila ampelophila Loew.]
[Illustration: Fig. 3.--The true house fly. Enlarged.]

WHERE THE TRUE HOUSE FLY LAYS ITS EGGS.
The true house fly (fig. 3), which is found in nearly all parts of the

world, is a medium-sized fly with four black stripes on the back and a
sharp elbow in one of the veins of the wings. The house fly can not bite,
its mouth parts being spread out at the tip for sucking up liquid
substances.
The eggs (figs. 4, 5) are laid upon horse manure. This substance seems
to be its favorite larval food. It will breed also in human excrement, and
because of this habit it is very dangerous to the health of human beings,
carrying as it does the germs of intestinal diseases, such as typhoid
fever and cholera, from the excreta to food supplies. It has also been
found to breed freely in hog manure, in considerable numbers in
chicken dung, and to some extent in cow manure. Indeed, it will lay its
eggs on a great variety of decaying vegetable and animal materials, but
of the flies that infest dwelling houses, both in cities and on farms, a
vast proportion come from horse manure.
[Illustration: FIG. 4.--Eggs of the house fly. About natural size.
(Newstead.)]
It often happens, however, that this fly is very abundant in localities
where little or no horse manure is found, and in such cases it breeds in
other manure, such as chicken manure in backyard poultry lots, or in
slops or fermenting vegetable material, such as spent hops, moist bran,
ensilage, or rotting potatoes. Accumulations of organic material on the
dumping grounds of towns and cities often produce flies in great
numbers.
[Illustration: FIG. 5.--Eggs of the house fly. Highly magnified.
(Newstead.)]
The house fly begins laying eggs in from 2 1/2 to 20 days after
emerging, the time interval depending to a large extent upon
temperature, humidity, and character and abundance of food. The
number of eggs laid by an individual fly at one time ranges from 120 to
159 and a single female will usually lay two and sometimes four such
batches. Dunn has recently reported that in Panama a fly may deposit as
many as 2,367 eggs in 21 batches, and sometimes an interval of only 36
hours may occur between the deposition of large batches of eggs. The

enormous numbers in which the insects occur are thus plainly
accounted for, especially when the abundance and universal occurrence
of appropriate larval food is considered. The eggs are deposited below
the surface in the cracks and interstices of the manure, several females
usually depositing in one spot, so that the eggs commonly are found in
large clusters (fig. 4) in selected places near the top of the pile, where a
high degree of heat is maintained by the fermentation below. The
second batch of eggs is laid from 8 to 10 days after the first. The eggs
usually hatch in less than 24 hours. Under the most favorable
conditions of temperature and moisture the egg state may last hardly
more than 8 hours. The maggots which issue from the eggs are very
small and transparent. They grow rapidly, completing the growth of the
larva stage in three days under the most favorable conditions, although
this stage usually lasts from 4 to 7 days. The larval period may be
prolonged greatly by low temperature or by dryness or scarcity of the
larval food. As the larvæ (fig. 6) attain full size they gradually assume a
creamy white color. A few hours before pupation they become very
restless and migrate from their feeding ground in search of a favorable
place in which to pass the pupa stage. They will often congregate at the
edges of manure piles near the ground or burrow into the soil beneath,
or they may crawl considerable distances away from the pile to pupate
in the ground or in loose material under the edges of stones, boards, etc.
[Illustration: FIG. 6.--Larvæ, or maggots, of the house fly. About
natural size. (Newstead.)]
The pupæ (fig 7), or "sleepers," are more or less barrel shaped and dark
brown in color. In midsummer this stage usually lasts from 3 to 6