Book: The House Fly and How to Suppress It
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L. O. Howard and F. C. Bishopp >> The House Fly and How to Suppress It
U. S. DEPARTMENT OF AGRICULTURE
FARMERS' BULLETIN No. 1408
_The_ HOUSE FLY AND HOW TO SUPPRESS IT
[Illustration: fly]
[Illustration: USDA seal]
The presence of flies is an indication of uncleanliness, insanitary
conditions, and improper disposal of substances in which they breed.
They are not only annoying; they are actually dangerous to health,
because they may carry disease germs to exposed foods.
It is therefore important to know where and how they breed, and to apply
such knowledge in combating them. This bulletin gives information on
this subject. Besides giving directions for ridding the house of flies
by the use of screens, fly papers, poisons, and flytraps, it lays
especial emphasis on the explanation of methods of eliminating breeding
places and preventing the breeding of flies.
This bulletin supersedes Farmers' Bulletin 851.
Washington, D. C. Issued April, 1925; revised November, 1926
THE HOUSE FLY[1] AND HOW TO SUPPRESS IT.
By L. O. HOWARD, _Chief of the Bureau of Entomology_, and F. C. BISHOPP,
_Entomologist_.
* * * * *
CONTENTS.
Page.
Kinds of flies found in houses 1
Where the true house fly lays its eggs 2
How the house fly passes the winter 6
Carriage of disease by the house fly 6
Excluding and capturing flies 7
The use of screens 7
Fly papers and poisons 8
Fly sprays 8
Flytraps 9
Preventing the breeding of flies 9
Construction and care of stables 9
Fly-tight manure pits 10
Frequency with which manure should be removed in cities and towns 10
Health office regulations for control of house flies in cities 10
Disposal of manure in rural and suburban districts 11
Chemical treatment of manure to destroy fly maggots 12
Maggot trap for destruction of fly larvae from horse manure 13
Compact heaping of manure 15
Garbage disposal and treatment of miscellaneous breeding places 15
Sewage disposal in relation to the prevention of fly-borne diseases 15
What communities can do to eliminate the house fly 16
* * * * *
KINDS OF FLIES FOUND IN HOUSES.
Several species of flies are found commonly in houses. Some of them so
closely resemble the true house fly that it requires very careful
observation to distinguish them from it.
One of these is the biting stable fly[2] (fig. 1). It occurs frequently
in houses and differs from the house fly in the important particular
that its mouth parts are formed for piercing the skin. This fly is so
often mistaken for the house fly that most people think that the house
fly can bite.
Another frequent visitant of houses, particularly in the spring and
fall, is the cluster fly.[3] It is somewhat larger than the house fly,
and is distinguished by its covering of fine yellowish hairs.
Occasionally this fly occurs in houses in such numbers as to cause great
annoyance. It gets its name of "cluster fly" from its habit of
collecting in compact groups or clusters in protected corners during
cold periods.
Several species of metallic greenish or bluish flies also are found
occasionally in houses. These include a blue-bottle fly,[4] the black
blowflies,[5] and the green-bottle (fig. 2) flies.[6] They breed in
decaying animal matter.
[Footnote 1: _Musca domestica_ L.]
[Footnote 2: _Stomoxys calcitrans_ L.]
[Footnote 3: _Pollenia rudis_ Fab.]
[Footnote 4: _Calliphora erythrocephala_ Meig.]
[Footnote 5: _Phormia regina_ Meig. and _P. terrae-novae_ Desv.]
[Footnote 6: _Lucilia caesar_ L., _L. sericata_ Meig., and other species
of the genus.]
There is still another species, smaller than any of those so far
mentioned, which is sometimes called the "lesser house fly."[7] This
insect is distinguished from the ordinary house fly by its paler and
more pointed body. The male, which is commoner than the female, has
large pale patches at the base of the abdomen, which are translucent
when the fly is seen on the window pane. These little flies are not the
young of the larger flies. Flies do not grow after the wings have once
expanded and dried.
[Footnote 7: _Fannia canicularis_ L.]
[Illustration: FIG. 1.--The stable fly. Much enlarged.]
[Illustration: FIG. 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 larvae (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.--Larvae, or maggots, of the house fly. About
natural size. (Newstead.)]
The pupae (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 days.
The pupa stage is easily affected by temperature changes and may be
prolonged during hibernation for as long as 4 or 5 months. Numerous
rearing experiments in various parts of the country have shown that the
shortest time between the deposition of eggs and the emergence of the
adult fly is 8 days, and 10 and 12 day records were very common.
The adult fly, upon emerging from the puparium, works its way upward
through the soil or manure and upon reaching the air it crawls about
while its wings expand and the body hardens and assumes its normal
coloration. In from 2 1/2 to 20 days, as previously stated, the female
is ready to deposit eggs. As in the case of other periods of its life
history, so the preoviposition period is prolonged considerably by the
lower temperatures of spring and fall. In midsummer, with a
developmental period of from 8 to 10 days from egg to adult, and a
preoviposition period of from 3 to 4 days, a new generation would be
started every 11 to 14 days. Thus the climate of the District of
Columbia allows abundance of time for the development of from 10 to 12
generations every season.
[Illustration: FIG. 7.--Pupae of the house fly. About natural size.
(Newstead.)]
Flies usually remain near their breeding places if they have plenty of
food, but experiments recently made at Dallas, Tex., show that they may
migrate considerable distances; in fact, house flies, so marked that the
particular individuals could be identified, have been recaptured in
traps as far as 13 miles from the place where they were liberated.
HOW THE HOUSE FLY PASSES THE WINTER.
The prevailing opinion that the house fly lives through the winter as an
adult, hiding in cracks and crevices of buildings, etc., appears to be
erroneous. Under outdoor conditions house flies are killed during the
first really cold nights, that is, when the temperature falls to about
15 deg. or 10 deg. F. In rooms and similar places protected from winds and
partially heated during the winter flies have been kept alive in cages
for long periods, but they never lived through the entire winter. In
longevity experiments one record of 70 days and another of 91 days was
obtained. No uncaged house flies were found during three seasons'
observations in unheated and only partially heated attics, stables,
unused rooms, etc., where favorable temperature conditions prevailed.
The common occurrence in such places of the cluster fly and a few other
species, which may be easily mistaken for the house fly, is responsible
for the prevailing belief as to the way the house fly overwinters. There
is therefore no reliable evidence whatever that adult house flies
emerging during October and November pass the winter and are able to
deposit their eggs the following spring, although they may continue
active in heated buildings until nearly the end of January. On the other
hand, there is evidence that house flies pass the winter as larvae and
pupae, and that they sometimes breed continuously throughout the winter.
In experiments at both Dallas, Tex., and Bethesda, Md., house flies have
been found emerging during April from heavily infested manure heaps
which had been set out and covered with cages during the preceding
autumn. In the Southern States, during warm periods in midwinter, house
flies may emerge and become somewhat troublesome; they frequently lay
eggs on warm days.
The second way in which the house fly may pass the winter is by
continuous breeding. House flies congregate in heated rooms with the
approach of the winter season. If no food or breeding materials are
present they eventually die. However, where they have access to both
food and suitable substances for egg laying they will continue breeding
just as they do outdoors during the summer. Even in very cold climates
there are undoubtedly many places, especially in cities, where house
flies would have opportunity to pass the winter in this manner.
CARRIAGE OF DISEASE BY THE HOUSE FLY.
The body of the house fly is covered thickly with hairs and bristles of
varying lengths, and this is especially true of the legs. Thus, when it
crawls over infected material it readily becomes loaded with germs, and
subsequent visits to human foods result in their contamination. Even
more dangerous than the transference of germs on the legs and body of
the fly is the fact that bacteria are found in greater numbers and live
longer in its alimentary canal. These germs are voided, not only in the
excrement of the fly, but also in small droplets of regurgitated matter
which have been called "vomit spots." When we realize that flies
frequent and feed upon the most filthy substances (it may be the excreta
of typhoid or dysentery patients or the discharges of one suffering from
tuberculosis), and that subsequently they may contaminate human foods
with their feet or excreta or vomit spots, the necessity and importance
of house-fly control is clear.
In army camps, in mining camps, and in great public works, where large
numbers of men are brought together for a longer or shorter time, there
is seldom the proper care of excreta, and the carriage of typhoid germs
from the latrines and privies to food by flies is common and often
results in epidemics of typhoid fever.
And such carriage of typhoid is by no means confined to great temporary
camps. In farmhouses in small communities, and even in badly cared for
portions of large cities, typhoid germs are carried from excrement to
food by flies, and the proper supervision and treatment of the breeding
places of the house fly become most important elements in the prevention
of typhoid.
In the same way other intestinal germ diseases, such as Asiatic cholera,
dysentery, enteritis (inflammation of the intestine), and infantile
diarrhea, are all so carried. There is strong circumstantial evidence
also that tuberculosis, anthrax, yaws, ophthalmia, smallpox, tropical
sore, and the eggs of parasitic worms may be and are carried in this
way. In the case of over 30 different disease organisms and parasitic
worms, actual laboratory proof exists, and where lacking is replaced by
circumstantial evidence amounting almost to certainty.
EXCLUDING AND CAPTURING FLIES.
The principal effort to control this dangerous insect must be made at
the source of supply--its breeding places. Absolute cleanliness and the
removal or destruction of anything in which flies may breed are
essential; and this is something that can be done even in cities.
Perhaps it can be done more easily in the cities than in villages, on
account of their greater police power and the lesser insistence on the
rights of the individual. Once people are educated to the danger and
learn to find the breeding places, the rest will be easy.
In spite of what has just been said, it is often necessary to catch or
otherwise destroy adult flies, or to protect food materials from
contamination and persons from annoyance or danger; hence the value of
fly papers and poisons, flytraps, and insect screens.
THE USE OF INSECT SCREENS.
A careful screening of windows and doors during the summer months, with
the supplementary use of sticky fly papers, is a protective measure
against house flies known to everyone. As regards screening, it is only
necessary here to emphasize the importance of keeping food supplies
screened or otherwise covered so that flies can gain no access to them.
This applies not only to homes but also to stores, restaurants, milk
shops, and the like. Screening, of course, will have no effect in
decreasing the number of flies, but at least it has the virtue of
lessening the danger of contamination of food.
Insect screens for doors and windows should be well made and must fit
tightly, otherwise they will not keep insects out. It is equally
important that they be made of good and durable screen cloth. Copper
insect screen cloth, although a little higher in price, will prove more
economical in the long run, as it lasts many years. If, however, the
cost of copper screen cloth is objectionable, steel screen cloth, either
painted or galvanized, can be used. Painted steel screen cloth will last
one or more years without repainting, its durability depending upon the
climate. In humid regions, of course, it will rust more quickly than it
will where the climate is dry. The same may be said of galvanized steel
insect screen cloth.
Insect screen cloth made with 16 meshes to the inch is recommended, for
16-mesh screen cloth will keep out flies and most mosquitoes[9] and
other small insects which at times are found almost everywhere.
[Footnote 9: Where the yellow fever or dengue fever mosquito occurs,
18-mesh screen cloth (or 16-mesh screen cloth made from extra heavy
wire) should be used.]
FLY PAPERS AND POISONS.
[Illustration: FIG. 8.--Conical hoop flytrap side view. _A_, Hoops
forming frame at bottom. _B_, Hoops forming frame at top. _C_, Top of
trap made of barrel head. _D_, Strips around door. _E_, Door frame. _F_,
Screen on door. _G_, Buttons holding door. _H_, Screen on outside of
trap. _I_, Strips on side of trap between hoops. _J_, Tips of these
strips projecting to form legs. _K_, Cone. _L_, United edges of screen
forming cone. _M_, Aperture at apex of cone. (Bishopp.)]
The use of sticky fly papers to destroy flies that have gained access to
houses is well known. Fly-poison preparations also are common. Many of
the commercial fly poisons contain arsenic, and their use in the
household is attended with considerable danger, especially to children.
This danger is less with the use of a weak solution of formalin. A very
effective fly poison is made by adding 3 teaspoonfuls of the commercial
formalin to a pint of milk or water sweetened with a little brown sugar.
A convenient way of exposing this poison is by partly filling an
ordinary drinking glass with the solution. A saucer or plate is then
lined with white blotting paper cut the size of the dish and placed
bottom up over the glass. The whole is then quickly inverted and a small
match stick placed under the edge of the glass. As the solution
evaporates from the paper more flows out from the glass and thus the
supply is automatically renewed.
FLY SPRAYS.
Sprays designed to destroy or repel house flies fill a certain need in
connection with the house-fly problem. No very satisfactory repellent
substances for this insect have been found which are at the same time
adaptable to general use about the home, or places where foods are
handled. Extracts of pyrethrum flowers are now generally available
commercially, and these give fairly good results in the destruction of
house flies in buildings. Most of the sprays of pyrethrum extract
contain kerosene oil as a carrier, and undoubtedly the kerosene has much
to do with the toxicity of the spray. Such materials are most applicable
to buildings which become infested with flies and which can be readily
closed up at night and the air within thoroughly saturated with the
spray by means of an atomizer. Under such conditions the flies are
rather quickly overcome by the spray and if a sufficient quantity is
used they will not revive.
FLYTRAPS.
Flytraps may be used to advantage in decreasing the number of flies.
Their use has been advocated not only because of the immediate results,
but because of the chances that the flies may be caught before they lay
eggs, and the number of future generations will be reduced greatly.
Many types of flytraps are on the market. As a rule the larger ones are
the more effective. Anyone with a few tools can construct flytraps for a
small part of the price of the ready-made ones. A trap (fig. 8) which is
very effective in catching flies and is easily made, durable, and cheap,
may be made of four barrel hoops, four laths, a few strips of boxing,
and 8 1/2 lineal feet of screening, 24 inches wide. (For greater details
see Farmers' Bulletin 734.)
The effectiveness of the traps will depend on the selection of baits. A
good bait for catching house flies is 1 part of blackstrap molasses to 3
parts of water, after the mixture has been allowed to ferment for a day
or two. Overripe or fermenting bananas crushed and placed in the bait
pans give good results, especially with milk added to them. A mixture of
equal parts brown sugar and curd of sour milk, thoroughly moistened,
gives good results after it has been allowed to stand for three or four
days.
PREVENTING THE BREEDING OF FLIES.
As previously stated, fly papers, poisons, and traps are at best only
temporary expedients. The most logical method of abating the fly
nuisance is the elimination or treatment of all breeding places. It
would appear from what is known of the life history and habits of the
common house fly that it is perfectly feasible for cities and towns to
reduce the numbers of this annoying and dangerous insect so greatly as
to render it of comparatively slight account. On farms also, in dairies,
and under rural conditions generally, much can and should be done to
control the fly, which here, as elsewhere, constitutes a very serious
menace to health.
CONSTRUCTION AND CARE OF STABLES.
In formulating rules for the construction and care of stables and the
disposal of manure the following points must be taken into
consideration. In the first place, the ground of soil-floor stables may
offer a suitable place for the development of fly larvae. The larvae will
migrate from the manure to the soil and continue their growth in the
moist ground. This takes place to some extent even when the manure is
removed from the stables every day. Even wooden floors are not entirely
satisfactory unless they are perfectly water-tight, since larvae will
crawl through the cracks and continue their development in the moist
ground below. Water-tight floors of concrete or masonry, therefore, are
desirable. Flies have been found to breed in surprising numbers in small
accumulations of material in the corners of feed troughs and mangers,
and it is important that such places be kept clean.
FLY-TIGHT MANURE PITS.
The Bureau of Entomology for a number of years has advised that manure
from horse stables be kept in fly-tight pits or bins. Such pits can be
built in or attached to the stable so that manure can be easily thrown
in at the time of cleaning and so constructed that the manure can be
readily removed. It is desirable that the manure be placed in these
fly-proof receptacles as soon as possible after it is voided. The
essential point is that flies be prevented from reaching the manure, and
for this reason the pit or bin must be tightly constructed, preferably
of concrete, and the lid kept closed except when the manure is being
thrown in or removed. The difficulty has been that manure often becomes
infested before it is put into the container, and flies frequently breed
out before it is emptied and often escape through the cracks. To obviate
these difficulties a manure box or pit with a modified tent trap or cone
trap attached is desirable.
In order to retain the fertilizing value of manure to the greatest
extent it is advisable that air be excluded from it as much as possible
and that it be protected from the leaching action of rains. This being
the case, there is really no necessity for covering a large portion of
the top of the box with a trap, but merely to have holes large enough to
attract flies to the light, and to cover these holes with ordinary
conical traps, with the legs cut off, so, that the bottoms of the traps
will fit closely to the box. The same arrangement can be made where
manure is kept in a pit. If manure boxes or pits are kept fly tight they
are satisfactory under farm or dairy conditions for the storage of
manure during the busy season when it can not be hauled out daily.