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                         Issued July 31, 1911.

                   U. S. DEPARTMENT OF AGRICULTURE.



                        FARMERS' BULLETIN 459.



                             HOUSE FLIES.



                                  BY

                             L. O. HOWARD,
                  _Chief of the Bureau of Entomology_.


                            [Illustration]


                              WASHINGTON:
                      GOVERNMENT PRINTING OFFICE.
                                 1911.




                         LETTER OF TRANSMITTAL


                                U. S. Department of Agriculture,
                                              Bureau of Entomology,
                                      _Washington, D. C, May 23, 1911_.

Sir: I have the honor to transmit for publication a paper dealing with
the subject of the house fly or typhoid fly. Previous publications of
this department concerning this insect have been in circular form, but
it is desired to make this information more widely available through
the medium of a Farmers' Bulletin. With this intention this manuscript
has been prepared, being modified and amplified from Circular No. 71 of
this bureau, and I respectfully recommend its publication as a Farmers'
Bulletin.

        Respectfully,

                                                L. O. Howard,
                                    _Entomologist and Chief of Bureau_.

        Hon. James Wilson,
    _Secretary of Agriculture_.


[A list giving the titles of all Farmers' Bulletins available for
distribution will be sent free upon application to a Member of Congress
or the Secretary of Agriculture.]




CONTENTS.


                                                                 Page.

  Introduction                                                       5

  Life history of the true house fly                                 7

  Carriage of disease                                                9

  Remedies and preventives                                          10

  Natural enemies                                                   15

  What cities and towns can do                                      15




ILLUSTRATIONS.


                                                                 Page.

  1. The common house fly (_Musca domestica_); Puparium,
       adult, larva, and details                                     5

  2. The biting house fly (_Stomoxys calcitrans_): Adult,
       larva, puparium, and details                                  6

  3. A stable fly (_Muscina stabulans_): Adult, larva,
       and details                                                   7

  4. One of the blue-bottle flies (_Phormia terrænovæ_): Adult       8

  5. The green-bottle fly (_Lucilia cæsar_): Adult                   8

  6. The little house fly (_Homalomyia brevis_): Adults and larva    9

  7. The fruit fly (_Drosophila ampelophila_): Adult, larva,
       puparium, and details.                                       10

  8. The dung fly (_Sepsis violacea_): Adult, puparium, and
       details                                                      11

  9. The house centipede (_Scutigera forceps_): Adult               14




HOUSE FLIES.



INTRODUCTION.


There are several species of flies which are commonly found in houses,
although but one of these should be called the house fly proper. This
is the _Musca domestica_ L. (fig. 1 ) and is a medium-sized, grayish
fly, with its mouth parts spread out at the tip for sucking up liquid
substances. It is found in nearly all parts of the world. On account
of the conformation of its mouth parts, the house fly can not bite,
yet no impression is stronger in the minds of most people than that
this insect does occasionally bite. This impression is due to the
frequent occurrence in houses of another fly (_Stomoxys calcitrans_
L.) (fig. 2), which is called the stable fly, and which, while closely
resembling the house fly (so closely, in fact, as to deceive anyone
but an entomologist), differs from it in the important particular
that its mouth parts are formed for piercing the skin. It is perhaps
second in point of abundance to the house fly in most portions of the
Northeastern States. It breeds in horse manure, cow manure, and in warm
decaying vegetation like old straw and grass heaps.

[Illustration: Fig. 1.--The common house fly (_Musca domestica_):
Puparium at left; adult next; larva and enlarged parts at right. All
enlarged. (Author's Illustration.)]

A third species, commonly called the cluster fly (_Pollenia rudis_
Fab.), is a very frequent visitant of houses, particularly in the
spring and fall. This fly is somewhat larger than the house fly, with a
dark-colored, smooth abdomen and a sprinkling of yellowish hairs. It is
not so active as the house fly and, particularly in the fall, is very
sluggish. At such times it may be picked up readily and is very subject
to the attacks of a fungous disease which causes it to die upon window
panes, surrounded by a whitish efflorescence. Occasionally this fly
occurs in houses in such numbers as to cause great annoyance, but such
occurrences are comparatively rare. It is said in its earlier stages to
be parasitic on certain angleworms.

A fourth species is another stable fly, known as _Muscina stabulans_
Fall. (fig. 3), a form which almost exactly resembles the house fly in
general appearance, and which does not bite as does the biting stable
fly. It breeds in decaying vegetable matter and in excrement.

[Illustration: Fig. 2.--The stable fly or biting house fly (_Stomoxys
calcitrans_): Adult, larva, puparium, and details. All enlarged.
(Author's illustration.)]

Several species of metallic greenish or bluish flies are also
occasionally found in houses, the most abundant of which is the
so-called blue-bottle fly (_Calliphora erythrocephala_ Meig.). This
insect is also called the blow-fly or meat-fly and breeds in decaying
animal material. A smaller species, which may be called the small
blue-bottle fly, is _Phormia terrænovæ_ Desv. (fig. 4); and a third,
which is green or blue in color and a trifle smaller than the large
blue-bottle, is _Lucilia cæsar_ L. (fig. 5).

There is still another species, smaller than any of those so far
mentioned, which is known to entomologists as _Homalomyia canicularis_
L., sometimes called the small house fly. A related species, _H.
brevis_ Rond., is shown in figure 6. _H. canicularis_ is distinguished
from the ordinary house fly by its paler and more pointed body and
conical shape. The male, which is much commoner than 'the female, has
large pale patches at the base of the abdomen, which are translucent
when the fly is seen on a window pane. It is this species that is
largely responsible for the prevalent idea that flies grow after
gaining wings. Most people think that these little Homalomyias are
the young of the larger flies, which, of course, is distinctly not
the case. They breed in decaying vegetable material, in the excreta of
animals, and in dead insects.

Still another fly, and this one is still smaller, is a jet-black
species known as the window fly (_Scenopinus fenestralis_ L.), which
in fact has become more abundant of later years. Its larva is a white,
very slender, almost thread-like creature, and is found in cracks of
the floor in buildings, where it feeds on other small insects.

In the autumn, when fruit appears on the sideboard, many specimens of
a small fruit-fly (_Drosophila ampelophila_ Loew) (fig. 7) make their
appearance, attracted by the odor of overripe fruit.

A small, slender fly is not infrequently seen in houses, especially
upon window panes. This is _Sepsis violacea_ Meig., shown enlarged in
figure 8.

[Illustration: Fig. 3.--A stable fly (_Muscina stabulans_): Adult,
larva, and details. All enlarged. (Author's Illustration.)]

All of these species, however, are greatly dwarfed in numbers by the
common house fly. In 1900 the writer made collections of the flies in
dining rooms in different parts of the country, and out of a total of
23,087 flies 22,808 were _Musca domestica_--that is, 98.8 per cent of
the whole number captured. The remainder, consisting of 1.2 per cent of
the whole, comprised various species, including those mentioned above.


LIFE HISTORY OF THE TRUE HOUSE FLY.

_Musca domestica_ commonly lays its eggs upon horse manure. This
substance seems to be its favorite larval food. It will oviposit on
cow manure, but we have not been able to rear it in this substance.
It will also breed in human excrement, and from this habit it becomes
very dangerous to the health of human beings, carrying, as it does,
the germs of intestinal diseases such as typhoid fever and cholera from
excreta to food supplies. It will also lay its eggs upon other decaying
vegetable and animal material, but of the flies that infest dwelling
houses, both in cities and on farms, a vast proportion comes from horse
manure.

[Illustration: Fig. 4.--One of the blue-bottle flies (_Phormia
terrænovæ_): Adult, enlarged. ( Author's Illustration.)]

It often happens, however, that this fly is very abundant in localities
where there is little or no horse manure, and in such cases it will
be found breeding in other manure or in slops or fermenting vegetable
material, such as spent hops, or bran, or ensilage.

At Salem, Mass., Packard states that he reared a generation in 14
days in horse manure. The duration of the egg state was 24 hours, the
larval state from 5 to 7 days, and the pupal state from 5 to 7 days.
At Washington the writer has found in midsummer that each female lays
at one time about 120 eggs, which hatch in 8 hours, the larval period
lasting 5 days and the pupal 5 days, making the total time for the
development of the generation 10 days. This was at the end of June. The
periods of development vary with the climate and with the season, and
the insect hibernates in the puparium condition in manure or at the
surface of the ground under a manure heap. It also hibernates in houses
as adult, hiding in crevices.

The Washington observations indicate that the larvæ molt twice, and
that there are thus three distinct larval stages.

The periods of development were found to be about as follows: Egg
from deposition to hatching, one-third of a day; hatching of larva
to first molt, 1 day; first to second molt, 1 day; second molt to
pupation, 3 days; pupation to issuing of adult, 5 days; total life
round, approximately 10 days. There is thus abundance of time for the
development of 12 or 13 generations in the climate of Washington every
summer.

[Illustration: Fig. 5.--The green-bottle fly (_Lucilia cæsar_): Adult,
enlarged. (Author's Illustration.)]

The number of eggs laid by an individual fly at one time is undoubtedly
large, averaging about 120, and a single female may lay 4 such batches,
so that the enormous numbers in which the insects occur is thus plainly
accounted for, especially when the abundance and universal occurrence
of appropriate larval food is considered. In order to ascertain the
numbers in which house-fly larvæ occur in horse-manure piles, a quarter
of a pound of rather well-infested horse manure was taken on August 9,
and in it were counted 160 larvæ and 146 puparia. This would make about
1,200 house flies to the pound of manure. This, however, can not be
taken as an average, since no larvæ are found in perhaps the greater
part of ordinary horse-manure piles. Neither, however, does it show
the limit of what can be found, since about 200 puparia were found in
less than 1 cubic inch of manure taken from a spot 2 inches below the
surface of the pile where the larvæ had congregated in immense numbers.
The different stages of the insect are well illustrated in figure 1 and
need no description.

[Illustration: Fig. 6.--The little house fly (_Homalomyia brevis_):
Female at left; male next, with enlarged antenna; larva at right. All
enlarged. (Author's Illustration.)]


CARRIAGE OF DISEASE.

In army camps, in mining camps, and in great public works, bringing
together large numbers of men 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 by flies is by no means confined to these
great temporary camps. In farmhouses in small communities and even
in the 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 are carried by flies.
The Asiatic cholera, dysentery, and infantile diarrhea are all so
carried.

Nor are the disease-bearing possibilities of the house fly limited to
intestinal germ diseases. There is strong circumstantial evidence that
tuberculosis, anthrax, yaws, ophthalmia, smallpox, tropical sore, and
parasitic worms may be and are so carried. Actual laboratory proof
exists in the cases of a number of these diseases, and where lacking is
replaced by circumstantial evidence amounting almost to certainty.


REMEDIES AND PREVENTIVES.

A careful screening of windows and doors during the summer months, with
the supplementary use of sticky fly papers, is a preventive measure
against house flies known to everyone, and there seems to be little
hope in the near future of much relief by doing away with the breeding
places. A single stable in which a horse is kept will supply house
flies for an extended neighborhood. People living in agricultural
communities will probably never be rid of the pest, but in cities,
with better methods of disposal of garbage and with the lessening of
the number of horses and horse stables consequent upon electric street
railways, bicycles, and automobiles, the time may come, and before
very long, when window screens may be discarded. The prompt gathering
of horse manure, which may be variously treated or kept in a specially
prepared receptacle, would greatly abate the fly nuisance, and city
ordinances compelling horse owners to follow some such course are
desirable. Absolute cleanliness, even under existing circumstances,
will always result in a diminution of the numbers of the house fly,
and, in fact, most household insects are less attracted to the premises
of what is known as the old-fashioned house-keeper than to those of the
other kind.

[Illustration: Fig. 7.--The fruit fly (_Drosophila ampelophila_): _a_,
Adult; _b_, antenna of same; _c_, base of tibia and first tarsal joint
of same; _d_, puparium, side view; _e_, puparium from above; _f_,
full-grown larva; _g_, anal spiracles of same. All enlarged. (Author's
illustration.)]

Not only must all horse stables be cared for, but chicken yards,
piggeries, and garbage receptacles as well, and absolutely sanitary
privies are prime necessities. Directions for building and caring for
such privies will be found in Farmers' Bulletin No. 463. The dry-earth
treatment of privy vaults is unsatisfactory. Kerosene should be used.

[Illustration: Fig. 8.--The dung fly (_Sepsis violacea_): Adult,
puparium, and details. All enlarged. (Author's illustration.)]

During the summer of 1897 a series of experiments was carried out
with the intention of showing whether it would be possible to treat
a manure pile in such a way as to stop the breeding of flies. The
writer's experience with the use of air-slaked lime on cow manure to
prevent the breeding of the horn fly (_Hæmatobia serrata_ Rob.-Desv.)
suggested experimentation with different lime compounds. It was found
to be perfectly impracticable to use air-slaked lime, land plaster, or
gas lime with good results. Few or no larvæ were killed by a thorough
mixing of the manure with any of these three substances. Chlorid of
lime, however, was found to be an excellent maggot killer. Where 1
pound of chlorid of lime was mixed with 8 quarts of horse manure, 90
per cent of the maggots were killed in less than 24 hours. At the rate
of one-fourth of a pound of chlorid of lime to 8 quarts of manure,
however, the substance was found not to be sufficiently strong. Chlorid
of lime, though cheap in Europe, costs at least 3-1/2 cents a pound in
large quantities in this country, so that the frequent treatment of a
large manure pile with this substance would be out of the question in
actual practice.

Experiments were therefore carried on with kerosene. It was found that
8 quarts of fresh horse manure sprayed with 1 pint of kerosene, which
was afterwards washed down with 1 quart of water, was thoroughly rid
of Irving maggots. Every individual was killed by the treatment. This
experiment and others of a similar nature on a small scale were so
satisfactory that it was considered at the close of the season that
a practical conclusion had been reached, and that it was perfectly
possible to treat any manure pile economically and in such a way as to
prevent the breeding of flies.

Practical work in the summer of 1898, however, demonstrated that this
was simply another case where an experiment on a small scale has failed
to develop points which in practical work would vitiate the results.

The stable of the United States Department of Agriculture, in which
about 12 horses were kept, was situated about 100 yards behind the
main building of the department and about 90 yards from the building
in which the Bureau of Entomology is situated. This stable was always
very carefully kept. The manure was thoroughly swept up every morning,
carried outside of the stable, and deposited in a pile behind the
building. This pile, after accumulating for a week or 10 days, or
sometimes 2 weeks, was carried off by the gardeners and spread upon
distant portions of the grounds. At all times in the summer this manure
pile swarmed with the maggots of the house fly. It is safe to say that
on an average many thousands of perfect flies issued from it every day,
and that at least a large share of the flies which constantly bothered
the employees in the two buildings mentioned came from this source.

On the basis of the experiments of 1897, an attempt was made, beginning
early in April, 1898, to prevent the breeding of house flies about the
department by the treatment of this manure pile with kerosene. The
attempt was begun early in April and was carried on for some weeks.
While undoubtedly hundreds of thousands of flies were destroyed in the
course of this work, it was found by the end of May that it was far
from perfect, since if used at an economical rate the kerosene could
not be made to penetrate throughout the whole pile of manure, even
when copiously washed down with water. A considerable proportion of
house-fly larvæ escaped injury from this treatment, which at the same
time was found, even at an economical cost, to be laborious, and such a
measure, in fact, as almost no one could be induced to adopt.

There remained, however, another measure which had been suggested by
the writer in an article on the house fly published in 1895, namely,
the preparation of an especial receptacle for the manure; and this
was very readily accomplished. A closet 6 by 8 feet had been built
in the corner of the stable nearest the manure pile. It had a door
opening into the stable proper, and also a window. A door was built in
the outside wall of this closet, and the stablemen were directed to
place no more manure outside the building; in other words, to abolish
the outside manure pile, and in the future to throw all of the manure
collected each morning into this closet, the window of which in the
meantime had been furnished with a wire screen. The preparations were
completed by the middle of June, and a barrel of chlorid of lime was
put in the corner of the closet. Since that time every morning the
manure of the stable is thrown into the closet, and a small shovelful
of chlorid of lime is scattered over it. At the expiration of 10 days
or 2 weeks the gardeners open the outside door, shovel the manure into
a cart, and carry if off to be thrown upon the grounds.

Judging from actual examination of the manure pile, the measure is
eminently successful. Very few flies are breeding in the product of
the stable which formerly gave birth to many thousands daily. After
this measure had been carried on for two weeks, employees of the
department who had no knowledge of the work that was going on were
asked whether they had noticed any diminution in the number of flies in
their offices. Persons in all of the offices on the first floor of the
two buildings were asked this question. In every office except one the
answer was that a marked decrease had been noticed, so that the work
must be considered to have been successful.

The account of this remedial work has been given with some detail,
since it shows so plainly that care and cleanliness combined with
such an arrangement as that described will in an individual stable
measurably affect the fly nuisance in neighboring buildings.

With the combined efforts of the persons owning stables in a given
community, much more effective results can undoubtedly be gained.

In the consideration of these measures we have not touched upon the
remedies for house flies breeding in human excrement. On account of
the danger of the carriage of typhoid fever, the dropping of human
excrement in the open in cities or towns, either on vacant lots or
in dark alleyways, should be made a misdemeanor, and the same care
should be taken by the sanitary authorities to remove or cover up such
depositions as is taken in the removal of the bodies of dead animals.
The box privy is always a nuisance from many points of view, and is
undoubtedly dangerous as a breeder of flies which may carry the germs
of intestinal disease. No box privies should be permitted to exist
unless they are conducted on the kerosene principle. With a proper
vault or other receptacle, closed except from above, and a free use of
kerosene and water, the breeding of house flies can be prevented.

[Illustration: Fig. 9.--The house centipede (_Scutigera forceps_) Adult
natural size (After Marlatt.)]

A Parisian journal, the Matin, during the winter of 1905-6, established
a prize of 10,000 francs for the best essay on the destruction of the
house fly. The jury of competent scientific men awarded the prize to
the author of a memoir in which it was proposed to use residuum oil in
the destruction of the eggs and larvæ of the fly. This oil is to be
used in privies and cesspools. Two liters per superficial meter of the
pit is mixed with water, stirred with a stick of wood, and then thrown
into the receptacle. It is said to form a covering of oil which kills
all the larvæ, preventing the entrance of flies into the pit and, at
the same time, the hatching of eggs. It makes a protective covering for
the excrement, and this is said to hasten the development of anærobic
bacteria as in a true septic pit, leading in this way to the rapid
liquefaction of solid matters and rendering them much more unfit for
the development of other bacteria. For manure it is recommended to mix
this residuum oil with earth, with lime, and with phosphates, and to
spread it at different times, in the spring by preference, upon the
manure of farms and stables and so on.

There seems to be a definite period of perhaps 10 days between the
issuing of the adult flies and the laying of eggs. During this period,
and especially in the early spring, it becomes important to trap as
many flies as possible. With this end in view, Prof. C. F Hodge, of
Clark University, Worcester, Mass., has devised certain flytraps which
he attaches to garbage cans and to screened stable windows, and which
he places in the neighborhood of possible fly-breeding places.

So many cheap flytraps are on the market that it is unnecessary and
undesirable to specify any particular kind. Many of them are good.


NATURAL ENEMIES.

The house fly has a number of natural enemies. The common house
centipede (fig. 9) destroys it in considerable numbers, there is a
small reddish mite which frequently covers its body and gradually
destroys it, it is subject to the attacks of hymenopterous parasites in
its larval condition, and it is destroyed by predatory beetles at the
same time.

The most effective enemy, however, is a fungous disease known as
_Empusa muscæ_, which carries off flies in large numbers, particularly
toward the close of the season. The epidemic ceases in December, and
although many thousands are killed by it, the remarkable rapidity of
development in the early summer months soon more than replaces the
thousands thus destroyed.


WHAT CITIES AND TOWNS CAN DO.

It would appear, from what we know of the life history of the common
house fly and from what remedial experimentation has already been
carried on, that it is perfectly feasible for cities and towns
to reduce the numbers of these annoying and dangerous insects so
greatly as to render them of comparatively slight account. The health
departments of most of our cities have the authority to abate nuisances
dangerous to health, and it is easy for the health authorities of any
city to formulate rules concerning the construction and care of stables
and the keeping and disposal of manure which, if enforced, will do away
with the house-fly nuisance. Such a series of rules was formulated in
the spring of 1906 by the Health Department of the city of Asheville,
N. C, and an effort is being made during this summer to see that they
are enforced. On the 3d of May, 1906, the Health Department of the
District of Columbia also issued a series of orders of this nature, on
the authority of the Commissioners of the District, and these orders,
which may well serve as a model to other communities desiring to
undertake similar measures, may be briefly condensed as follows:

All stalls in which animals are kept shall have the surface of the
ground covered with a water-tight floor. Every person occupying a
building where domestic animals are kept shall maintain, in connection
therewith, a bin or pit for the reception of manure, and, pending the
removal from the premises of the manure from the animal or animals,
shall place such manure in said bin or pit. This bin shall be so
constructed as to exclude rain water, and shall in all other respects
be water tight except as it may be connected with the public sewer.
It shall be provided with a suitable cover and constructed so as to
prevent the ingress and egress of flies. No person owning a stable
shall keep any manure or permit any manure to be kept in or upon any
portion of the premises other than the bin or pit described, nor shall
he allow any such bin or pit to be overfilled or needlessly uncovered.
Horse manure may be kept tightly rammed into well-covered barrels for
the purpose of removal in such barrels. Every person keeping manure in
any of the more densely populated parts of the District shall cause all
such manure to be removed from the premises at least twice every week
between June 1 and October 31, and at least once every week between
November 1 and May 31 of the following year. No person shall remove or
transport any manure over any public highway in any of the more densely
populated parts of the District except in a tight vehicle which, if not
inclosed, must be effectually covered with canvas, so as to prevent the
manure from being dropped. No person shall deposit manure removed from
the bins or pits within any of the more densely populated parts of the
District without a permit from the health officer. Any person violating
any of the provisions shall, upon conviction thereof, be punished by a
fine of not more than $40 for each offense.

As with all such measures, the test comes with the enforcement, and
these regulations have not been well enforced, owing to the extremely
small corps of inspectors allowed to the Health Department, and to
other more pressing work. They can be made effective, however, and
it is earnestly hoped that not only Washington but other communities
as well will very soon be brought to a realization of the ease of
house-fly eradication and its very great desirability.


       *       *       *       *       *


=The insect we now call the "house fly" should in the future be termed
the "typhoid fly," in order to call direct attention to the danger of
allowing it to continue to breed unchecked.--L. O. Howard.=


       *       *       *       *       *


Transcriber Notes

All illustrations moved to avoid splitting paragraphs.