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<p style="text-align:center; margin-top:0em; padding-top:.5em; font-size:2.5em; margin-bottom:0; background-color:#ffffff; color:#000000;"   >U. S. DEPARTMENT OF<br />AGRICULTURE</p>

<p style="font-size:1.5em; margin-bottom:0em; margin-top:0; padding-bottom:.5em; background-color:#ffffff; color:#000000;" class="center bb">
FARMERS' BULLETIN No. 1408</p>

<p style="margin-bottom:0; padding-top:1em; margin-top:0; font-size:2.5em; font-weight:bold; text-align:center;" ><i>The</i><br />
HOUSE FLY AND HOW<br />
TO SUPPRESS IT</p>

<img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-0.gif" style="width:20em; margin-left:7em; margin-right:7em; padding-top: 2em; text-align:center; z-index:1; clear:both;" class="center" alt="cover image" title="cover image" /><br />
<img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-usda.gif" style="width:9em; position:relative; float:left; z-index:2; margin-left:-1em; margin-top:-1em; clear:both;" alt="USDA logo" title="USDA logo" /><br /></div>
<p><br /></p>

<p><span class="pagenum"><a name="Page_1" id="Page_1"> -1- </a></span></p>

<div class="bbox" style="width:30em; padding-left:2em; padding-right:2em;"><p class="dropcap">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.</p>

<p>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.</p>

<p>This bulletin supersedes Farmers' Bulletin 851.</p>

<p class="bt"><br />Washington, D. C. Issued April, 1925; revised November, 1926</p>
</div>

<p><span class="pagenum"><a name="Page_2" id="Page_2"> -2- </a></span></p><h1>
THE HOUSE FLY<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor" style="font-size:.5em;" >[1]</a> AND HOW<br />
TO SUPPRESS IT.</h1>

<p class="center">By <span class="smcap">L. O. Howard</span>, <i>Chief of the Bureau of Entomology</i>, and <span class="smcap">F. C. Bishopp</span>,
<i>Entomologist</i>.</p>



<hr style="width: 65%;" />
<h2>CONTENTS.</h2>

<table class="toc" summary="table of contents">
<tr><td colspan="2" class="right"><span>Page.</span></td></tr>
<tr><td>Kinds of flies found in houses </td><td> &nbsp;<a href="#Page_1">1</a></td></tr>
<tr><td>Where the true house fly lays its eggs </td><td> &nbsp;<a href="#Page_2">2</a></td></tr>
<tr><td>How the house fly passes the winter </td><td> &nbsp;<a href="#Page_6">6</a></td></tr>
<tr><td>Carriage of disease by the house fly </td><td> &nbsp;<a href="#Page_6">6</a></td></tr>
<tr><td>Excluding and capturing flies </td><td> &nbsp;<a href="#Page_7">7</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >The use of screens </span></td><td> &nbsp;<a href="#Page_7">7</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Fly papers and poisons </span></td><td> &nbsp;<a href="#Page_8">8</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Fly sprays </span></td><td> &nbsp;<a href="#Page_8">8</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Flytraps </span></td><td> &nbsp;<a href="#Page_9">9</a></td></tr>
<tr><td>Preventing the breeding of flies </td><td> &nbsp;<a href="#Page_9">9</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Construction and care of stables </span></td><td> &nbsp;<a href="#Page_9">9</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Fly-tight manure pits </span></td><td><a href="#Page_10">10</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Frequency with which manure should be removed in cities and towns </span></td><td><a href="#Page_10">10</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Health office regulations for control of house flies in cities </span></td><td><a href="#Page_10">10</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Disposal of manure in rural and suburban districts </span></td><td><a href="#Page_11">11</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Chemical treatment of manure to destroy fly maggots </span></td><td><a href="#Page_12">12</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Maggot trap for destruction of fly larv&aelig; from horse manure </span></td><td><a href="#Page_13">13</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Compact heaping of manure </span></td><td><a href="#Page_15">15</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Garbage disposal and treatment of miscellaneous breeding places </span></td><td><a href="#Page_15">15</a></td></tr>
<tr><td><span style="margin-left: 2.5em;" >Sewage disposal in relation to the prevention of fly-borne diseases </span></td><td><a href="#Page_15">15</a></td></tr>
<tr><td>What communities can do to eliminate the house fly </td><td><a href="#Page_16">16</a></td></tr>
</table>


<hr style="width: 65%;" />
<h2>KINDS OF FLIES FOUND IN HOUSES.</h2>


<p class="dropcap">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.</p>

<p>One of these is the biting stable fly<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> (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.</p>

<p>Another frequent visitant of houses, particularly in the spring and
fall, is the cluster fly.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a> 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.</p>

<p>Several species of metallic greenish or bluish flies also are found
occasionally in houses. These include a blue-bottle fly,<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a> the black
blowflies,<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a> and the green-bottle (fig. 2) flies.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a> They breed in decaying
animal matter.</p>


<p><span class="pagenum"><a name="Page_3" id="Page_3"> -3- </a></span>There is still another species, smaller than any of those so far mentioned,
which is sometimes called the "lesser house fly."<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a> 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.</p>

<div class="twofly"><div class="figleft" style="clear:left;"><a href="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-1.gif"><img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-t1.jpg" class="smimg" alt="Fig. 1.--The stable fly. Much enlarged."
title="Fig. 1.--The stable fly. Much enlarged." /></a><p class="caption"><span class="smcap">Fig. 1.</span>&mdash; The stable fly. Much enlarged.</p></div>

<div class="figleft"><a href="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-2.gif"><img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-t2.jpg" class="smimg" alt="Fig. 2.--One of the green-bottle flies (Lucilia caesar). Much enlarged."
title="Fig. 2.--One of the green-bottle flies (Lucilia caesar). Much enlarged." /></a>
<p class="caption"><span class="smcap">Fig</span>. 2.&mdash; One of the green-bottle flies<br /> (<i>Lucilia caesar</i>). Much enlarged.</p></div></div>

<p style="clear:left;">In late summer and autumn many specimens of a small fruit fly,
known as the "vinegar fly,"<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a> make their appearance, attracted by the
odor of overripe fruit.</p>

<p>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.</p>


<h2>WHERE THE TRUE HOUSE FLY LAYS ITS EGGS.</h2>

<div class="figleft"><a href="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-3.gif"><img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-t3.jpg" class="smimg" alt="Fig. 3.--The true house fly.
Enlarged." title="Fig. 3.--The true house fly.
Enlarged." /></a><p class="caption"><span class="smcap">Fig. </span>3.&mdash; The true house fly.<br /> Enlarged.</p></div>
<p>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.</p>

<p>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
<span class="pagenum"><a name="Page_4" id="Page_4"> -4- </a></span>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.</p>

<div class="center caption"><a href="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-4.jpg"><img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-t4.jpg" class="bimg" alt="Fig. 4.--Eggs of the house fly.
About natural size. (Newstead.)" title="Fig. 4.--Eggs of the house fly. About natural size. (Newstead.)" /></a><br />
<span class="smcap">Fig</span>. 4.&mdash; Eggs of the house fly. About natural size. (Newstead.)</div>

<p>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.</p>

<div class="figleft"><a href="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-5.jpg"><img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-t5.jpg" class="smimg" alt="Fig. 5.--Eggs of the house fly. Highly
magnified. (Newstead.)" title="Fig. 5.--Eggs of the house fly. Highly
magnified. (Newstead.)" /></a><p class="caption"><span class="smcap">Fig.</span> 5.&mdash; Eggs of the house fly. <br />Highly
magnified. (Newstead.)</p></div>

<p>The house fly begins laying eggs
in from 2&#189; 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
<span class="pagenum"><a name="Page_5" id="Page_5"> -5- </a></span>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 larv&aelig; (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.</p>

<div class="caption center"><a href="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-6.jpg"><img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-t6.jpg" class="bimg" alt="Fig. 6.--Larv&aelig; , or maggots, of the house fly.
 About natural size. (Newstead.)" title="Fig. 6.--Larv&aelig; , or maggots, of the house fly. About natural size. (Newstead.)" /></a><br />
<span class="smcap">Fig</span>. 6.&mdash; Larv&aelig; , or maggots, of the house fly. About natural size. (Newstead.)</div>

<p><span class="pagenum"><a name="Page_6" id="Page_6"> -6- </a></span>The pup&aelig; (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.</p>

<p>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&#189; 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.</p>

<div class="caption center"><a href="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-7.jpg">
<img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-t7.jpg" class="bimg" title="Fig. 7.--Pup&aelig; of the house fly. About natural size. (Newstead.)"
 alt="Fig. 7.--Pup&aelig; of the house fly. About natural size. (Newstead.)" /></a><br />
 <span class="smcap">Fig</span>. 7.&mdash; Pup&aelig; of the house fly. About natural size. (Newstead.)</div>

<p>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.</p>


<p><span class="pagenum"><a name="Page_7" id="Page_7"> -7- </a></span></p>
<h2>HOW THE HOUSE FLY PASSES THE WINTER.</h2>


<p>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 larv&aelig; and pup&aelig; , 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.</p>

<p>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.</p>




<h2>CARRIAGE OF DISEASE BY THE HOUSE FLY.</h2>


<p>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
<span class="pagenum"><a name="Page_8" id="Page_8"> -8- </a></span>or vomit spots, the necessity and importance of house-fly control is
clear.</p>

<p>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.</p>

<p>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.</p>

<p>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.</p>



<h2>EXCLUDING AND CAPTURING FLIES.</h2>


<p>The principal effort to control this dangerous insect must be made
at the source of supply&mdash; 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.</p>

<p>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.</p>


<p class="bcenter"><b>THE USE OF INSECT SCREENS.</b></p>

<p>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.</p>

<p>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 depend<span class="pagenum"><a name="Page_9" id="Page_9"> -9- </a></span>ing
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.</p>

<p>Insect screen cloth made with 16 meshes to the inch is recommended,
for 16-mesh screen cloth will keep out flies and most mosquitoes<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a> and
other small insects which at times are found almost everywhere.</p>


<p class="bcenter"><b>FLY PAPERS AND POISONS.</b></p>

<div class="figleft"><a href="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-8.gif"><img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-t8.jpg" class="smimg" alt="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.)" title="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.)" /></a><br /><p class="caption" style="text-align:left;"><span class="smcap">Fig</span>. 8.&mdash; Conical hoop flytrap side view. <i>A</i>, Hoops forming
frame at bottom. <i>B</i>, Hoops forming frame at top.
<i>C</i>, Top of trap made of barrel head. <i>D</i>, Strips around
door. <i>E</i>, Door frame. <i>F</i>, Screen on door. <i>G</i>, Buttons
holding door. <i>H</i>, Screen on outside of trap. <i>I</i>, Strips
on side of trap between hoops. <i>J</i>, Tips of these strips
projecting to form legs. <i>K</i>, Cone. <i>L</i>, United edges of
screen forming cone. <i>M</i>, Aperture at apex of cone.
(Bishopp.)</p></div>

<p>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.</p>


<p class="bcenter"><b>FLY SPRAYS.</b></p>

<p>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
<span class="pagenum"><a name="Page_10" id="Page_10"> -10- </a></span>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.</p>


<p class="bcenter"><b>FLYTRAPS.</b></p>

<p>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.</p>

<p>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&#189; lineal feet of screening, 24
inches wide. (For greater details see Farmers' Bulletin 734.)</p>

<p>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.</p>




<h2>PREVENTING THE BREEDING OF FLIES.</h2>


<p>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.</p>


<p class="bcenter"><b>CONSTRUCTION AND CARE OF STABLES.</b></p>

<p>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 larv&aelig; . The larv&aelig;
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
<span class="pagenum"><a name="Page_11" id="Page_11"> -11- </a></span>are not entirely satisfactory unless they are perfectly water-tight,
since larv&aelig; 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.</p>


<p class="bcenter"><b>FLY-TIGHT MANURE PITS.</b></p>

<p>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.</p>

<p>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.</p>


<p class="bcenter"><b>FREQUENCY WITH WHICH MANURE SHOULD BE REMOVED IN CITIES AND TOWNS.</b></p>

<p>In deciding the question as to how often manure should be removed
in cities and towns, it should be borne in mind that when the
larv&aelig; have finished feeding they will often leave the manure and
pupate in the ground below or crawl some distance away to pupate
in d&eacute; bris under boards or stones and the like. Hence the manure
should be removed before the larv&aelig; reach the migratory stage; that
is to say, removal is necessary every three days, and certainly not less
frequently than twice a week during the summer months. A series
of orders issued in 1906 by the health department of the District of
Columbia, on the authority of the Commissioners of the District,
covers most of these points, and these orders, which may well serve
as a model to other communities desiring to undertake similar
measures, may be briefly condensed as follows:</p>
<p><span class="pagenum"><a name="Page_12" id="Page_12"> -12- </a></span></p>


<div class="blockquot"><b>HEALTH OFFICE REGULATIONS FOR CONTROL OF HOUSE FLIES IN CITIES.</b><br />
<p style="position:relative; text-indent:1.6em; margin-top:0;" >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 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.</p></div>

<p>Not only must horse stables be cared for, but chicken yards, piggeries,
and garbage receptacles as well. 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.</p>


<p class="bcenter"><b>DISPOSAL OF MANURE IN RURAL AND SUBURBAN DISTRICTS.</b></p>

<p>The control of flies in rural and suburban districts offers a much
more difficult problem. Here it is often out of the question to remove
all manure from the premises twice a week, and the problem is to
find some method of disposal or storage which will conserve the
fertilizing value of the manure and at the same time prevent all
flies from breeding, or destroy such as do breed there.</p>

<p>With this idea in mind, it has been recommended that stable
manure be collected every morning and hauled out at once and spread
rather thinly on the fields. This procedure is advisable from the
point of view of getting the maximum fertilizing value from the
manure. Immediate spreading on the fields is said largely to prevent
the loss of plant food which occurs when manure is allowed to stand
in heaps for a long time. This method will be effective in preventing
the breeding of flies only if the manure is hauled out promptly every
morning and spread thinly so that it will dry, since it is unfavorable
for fly development in desiccated condition. The proper scattering
of the manure on the fields is best and most easily and quickly accomplished
by the use of a manure spreader, and many dairies, and
even farms, are practicing the daily distribution of manure in this
way. Removal every three or four days will not be sufficient. Observations
have shown that if manure becomes flyblown and the
maggots attain a fairly good size before the manure is scattered on
the fields, they can continue their development and will pupate in the
ground.</p>


<p><span class="pagenum"><a name="Page_13" id="Page_13"> -13- </a></span></p>
<p class="bcenter"><b>CHEMICAL TREATMENT OF MANURE TO DESTROY FLY MAGGOTS.</b></p>

<p>During the summer months, when fly breeding is going on most
actively, the farmer is also busy and often can not spare the time to
remove manure regularly. The general practice, therefore, has been
to keep the manure in heaps located, as a rule, very near the stables.
How can fly breeding be prevented in such accumulations? As a
result of recent investigations, it is now possible to point out two
methods which are practical and effective.</p>

<p>The first is the treatment of the manure pile with chemical substances
which will kill the eggs and maggots of the house fly. The
Bureau of Entomology, in cooperation with the Bureau of Chemistry
and the Bureau of Plant Industry, has conducted a series of experiments
in which a large number of chemicals were applied to infested
manure and observations made, not only on their efficiency in killing
the maggots but also as to their effect on the chemical composition and
bacterial flora of the manure. The object was to find some cheap
chemical which would be effective in destroying the fly larv&aelig; and at
the same time would not reduce the fertilizing value of the manure.</p>


<p class="bcenter"><b>TREATMENT WITH HELLEBORE.</b></p>

<p>Of the numerous substances tried, the one which seems best to
fulfill these conditions is powdered hellebore.<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a> For the treatment of
manure a water extract of the hellebore is prepared by adding &#189;
pound of the powder to every 10 gallons of water, and after stirring
it is allowed to stand 24 hours. The mixture thus prepared is
sprinkled over the manure at the rate of 10 gallons to every 8 bushels
(10 cubic feet) of manure. From the result of 12 experiments with
manure piles treated under natural conditions it appears that such
treatment results in the destruction of from 88 to 99 per cent of the
fly larv&aelig; .</p>

<p>Studies of treated manure indicated that its composition and
rotting were not interfered with. Furthermore, several field tests
showed that there was no apparent injury to growing crops when
fertilized with treated manure.</p>

<p>Since the solution is somewhat poisonous it should not be left
exposed where it might be drunk by livestock. It is quite safe to
say that chickens will not be injured by pecking at hellebore-treated
manure. This has been tested carefully. Hellebore can be obtained
both in ground and powdered form, but the powder gives the best
results in the destruction of fly larv&aelig; .</p>


<p class="bcenter"><b>TREATMENT WITH POWDERED BORAX.</b></p>

<p>Another chemical found to be even more effective as a larvicide is
powdered borax. This substance is available in commercial form in
all parts of the country. It has the advantage of being comparatively
nonpoisonous and noninflammable and is easily transported
and handled. The minimum amount necessary to kill fly larv&aelig; was
found to be 0.62 pound per 8 bushels of manure, or about 1 pound per
16 cubic feet. Best results were obtained when the borax was applied
in solution, or when water was sprinkled on after the borax had been
scattered evenly over the pile. Borax is not only effective in killing
the larv&aelig; , but when it comes in contact with the eggs it prevents them
from hatching. When applied at the rate of 1 pound to 16 cubic feet
it was found to kill about 90 per cent of the larv&aelig; , heavier applications
killing from 98 to 99 per cent.</p>

<p><span class="pagenum"><a name="Page_14" id="Page_14"> -14- </a></span>Borax has no injurious effect on the chemical composition or rotting
of the manure. However, when added in large quantities with manure
to the soil it will cause considerable injury to growing plants.
A number of experiments have been conducted to determine the effect
on crops of the use of manure treated with borax as herein recommended.
When applied at the rate of 15 tons per acre it appears
that no injury as a rule will follow. Some crops are more sensitive
to borax than others, and also the tendency to injury appears to vary
on different soils. It is necessary, therefore, to repeat the warning
issued in connection with a previous bulletin<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a> on this subject, that
great care be exercised, in the application of borax, that the manure
does not receive more than 1 pound for every 16 cubic feet, and that
not more than 15 tons of manure so treated are applied to the acre.</p>

<p>In view of the possible injury from the borax treatment as a result
of carelessness in applying it, or from other unforeseen conditions, it
is recommended that horse manure and other farmyard manures
which are to be used as fertilizer be treated with hellebore. Borax,
on the other hand, is such a good larvicide that it call be used with
advantage on the ground of soil-floor stables, in privies, on refuse
piles, and on any accumulations of fermenting organic matter which
are not to be used for fertilizing purposes.</p>


<p class="bcenter"><b>TREATMENT WITH CALCIUM CYANAMID AND ACID PHOSPHATE.</b></p>

<p>Many experiments with mixtures of commercial fertilizers were
tried to determine whether fly larv&aelig; would be killed by any substance
the addition of which would increase the fertilizing value of
the manure. A mixture of calcium cyanamid and acid phosphate
was found to possess considerable larvicidal action. Several experiments
showed that &#189; pound of calcium cyanamid plus &#189; pound of
acid phosphate to each bushel of manure give an apparent larvicidal
action of 98 per cent. The mixture in the form of a powder was
scattered evenly over the surface and then wet down with water.
The use of this mixture adds to the manure two important elements,
nitrogen and phosphorus.</p>


<p class="bcenter"><b>MAGGOT TRAP FOR DESTRUCTION OF FLY LARV&AElig; FROM HORSE MANURE.</b></p>

<p>The second method of handling manure is one which does not require
the application of chemicals. It is based on the fact, mentioned
on page 4, that the larv&aelig; of the house fly, a few hours before they
are ready to pupate, show a strong tendency to migrate. This migration
takes place mostly at night, and the larv&aelig; sometimes crawl considerable
distances from the manure pile. Now it is possible by
means of a very simple arrangement called a maggot trap to destroy
fully 99 per cent of all maggots breeding in a given lot of manure.
A successful maggot trap which the Maryland Agricultural College
constructed at the college barn is shown in Figure 9. The trap was
designed by R. H. Hutchison and constructed under his supervision.
The manure, instead of being thrown on the ground, is heaped carefully
on a slatted platform, which stands about 1 foot high. This
<span class="pagenum"><a name="Page_15" id="Page_15"> -15- </a></span>particular platform measures 10 by 20 feet. There are six 2 by 4
pieces running lengthwise 2 feet apart. Across these are nailed
1-inch strips with &#189; to 1 inch spaces between them. The wooden
platform stands on a concrete floor, and a rim or wall of concrete
4 inches high surrounds the floor. The floor slopes a little toward
one corner from which a pipe leads to a small cistern near by. This
pipe is plugged with a stopper of soft wood, and the concrete floor
is filled with water to a depth of 1 inch in the shallowest part. Flies
will lay their eggs on the manure as usual, but the maggots, when
they have finished feeding and begin to migrate, crawl out of the
manure, drop into the water below, and are drowned. Each week
the plug is removed from the pipe, and all the maggots are washed
into the cistern. The floor is then cleaned of any solid particles by
means of a long-handled stable broom or by a strong stream of water
from a hose. The pipe being again plugged, the floor is again partly
filled with water and the trap is ready for another week's catch. A
platform of this size will hold the manure accumulating from four
horses during the period of four months, or about 20 days' accumulation
from 25 horses, if the heap is well built and made at least 5 feet
high.</p>


<div class="caption center"><a href="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-9.jpg"><img src="https://brian.carnell.com/wiki/_media/etext:l:lo-howard-the-house-fly-t9.jpg" class="bimg"
alt="Fig. 9.--A maggot trap for house-fly control. View showing the concrete basin containing
water in which larv&aelig; are drowned, and the wooden platform on which manure is
heaped. (Hutchison.)" title="Fig. 9.--A maggot trap for house-fly control. View showing the concrete basin containing
water in which larv&aelig; are drowned, and the wooden platform on which manure is
heaped. (Hutchison.)" /></a><br /><span class="smcap">Fig</span>. 9.
A maggot trap for house-fly control. View showing the concrete basin containing
water in which larv&aelig; are drowned, and the wooden platform on which manure is
heaped. (Hutchison.)</div>

<p>Experience with this maggot trap clearly indicates that best results
can be secured if the manure is compactly heaped on the platform
and kept thoroughly moistened. It is best to apply a small amount
of water each morning after the stable cleanings have been added
to the pile.
<span class="pagenum"><a name="Page_16" id="Page_16"> -16- </a></span>It should be borne in mind that in order to make this trap a success
the platform beneath the pile must be kept comparatively free
of accumulations of manure, and moisture applied regularly to drive
the maggots out.</p>


<p class="bcenter"><b>COMPACT HEAPING OF MANURE.</b></p>

<p>Another method of disposing of manure has been recommended
by English writers. The manure is built up in a compact rectangular
heap, the sides of which are beaten hard with shovels. The
ground around the edges of the heap is made smooth and hard and
loose straw is placed in small windrows around the manure pile
about 1 foot from the edge. The exclusion of the air, together
with the high temperature and gases formed by fermentation, tends
to make the heap unfavorable for the development of fly larv&aelig; .
Those which do happen to develop in the surface layers will migrate
and pupate in the ring of straw around the heap, where they are
destroyed by burning.</p>


<p class="bcenter"><b>GARBAGE DISPOSAL AND TREATMENT OF MISCELLANEOUS BREEDING PLACES.</b></p>

<p>It is just as true under farm conditions as in cities that breeding
places other than horse manure must be attended to. Garbage must
be disposed of, hog and poultry manure must be cared for, and especially
on dairy farms it is extremely important that every precaution
be taken to prevent the contamination of milk by flies.</p>

<p>It is very desirable that all refuse possible, accumulated from
cities and towns, be burned. Incineration has been practiced successfully
by a number of towns and cities with populations of from
10,000 to 15,000 and over. In larger cities provision should be
made for burning carcasses as well as garbage and other refuse. If
city and town garbage is sold to hog feeders the municipal authorities
should have control of the sanitary conditions about the feeding
yards, as there is great danger from fly breeding in such places if
not kept clean.</p>


<p class="bcenter"><b>SEWAGE DISPOSAL IN RELATION TO THE PREVENTION OF FLY-BORNE DISEASES.</b></p>

<p>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 in 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. For modern methods of sewage disposal adapted for
farm use one should consult Department of Agriculture Department
Bulletin No. 57. In the absence of modern methods of sewage disposal,
absolutely sanitary privies are prime necessities, whether in
towns or on farms. Directions for building and caring for such
privies will be found in Farmers' Bulletin 463 and in Yearbook
Separate 712, "Sewage Disposal on the Farm." The box privy is
<span class="pagenum"><a name="Page_17" id="Page_17"> -17- </a></span>always a nuisance from many points of view, and is undoubtedly
dangerous as a breeder of flies which may carry the germs of intestinal
diseases. The dry-earth treatment of privies is unsatisfactory.
No box privy should be permitted to exist unless it is thoroughly
and regularly treated with some effective larvicide. Since
the fecal matter in such privies is seldom used for fertilizing purposes
it may well be treated liberally with borax. The powdered
borax may be scattered two or three times a week over the exposed
surface so as to whiten it.</p>




<h2>WHAT COMMUNITIES CAN DO TO ELIMINATE THE HOUSE FLY.</h2>


<p>Antifly crusades have been very numerous in recent years, and
some have been noteworthy both in methods and in results. However,
it will not be amiss here to emphasize the importance of concerted,
organized effort on the part of whole communities, not only
cities, but suburban and rural neighborhoods as well. By the most
painstaking care one may prevent all fly breeding on his premises,
but it will avail him little if his neighbors are not equally careful.
Some sort of cooperation is necessary. One of the first and most
important elements in any antifly crusade is a vigorous and continued
educational campaign. It has been the experience of those
who have undertaken such crusades that people generally regard
the fly as a somewhat harmless nuisance and that the first work of
the campaign was to bring the people to a realization of the dangers
from flies and the possibility of getting rid of them. In the educational
campaign every possible means of publicity can be employed,
including newspapers, lectures, moving pictures, posters, handbills,
cartoons, instruction in schools, etc.</p>

<p>The antifly crusade is a matter of public interest and should be
supported by the community as a whole and engineered by the health
officers. But health officers can do little toward the necessary work
of inspection and elimination without funds, and therefore the support
of the campaign must manifest itself in increased appropriations
for public-health work. Very often it is lack of funds which
prevents the health officers from taking the initiative in the antifly
crusades, and there must necessarily be much agitation and education
before they can profitably take up the work. Right here lies
a field for civic associations, women's clubs, boards of trade, etc.,
to exercise their best energy, initiative, and leadership.</p>



<p><span class="pagenum"><a name="Page_18" id="Page_18"> -18- </a></span></p>
<h2>ORGANIZATION OF THE UNITED STATES DEPARTMENT OF AGRICULTURE WHEN THIS PUBLICATION WAS LAST PRINTED</h2>

<table summary="ORGANIZATION OF THE UNITED STATES DEPARTMENT OF AGRICULTURE WHEN THIS PUBLICATION WAS LAST PRINTED">
<tr><td class="roles">Secretary of Agriculture</td><td> <span class="smcap">Arthur M. Hyde.</span></td></tr>
<tr><td>Assistant Secretary</td><td> <span class="smcap">R. W. Dunlap.</span></td></tr>
<tr><td>Director of Scientific Work</td><td> <span class="smcap">A. F. Woods.</span></td></tr>
<tr><td>Director of Regulatory Work</td><td> <span class="smcap">Walter G. Campbell.</span></td></tr>
<tr><td>Director of Extension Work</td><td> <span class="smcap">C. W. Warburton.</span></td></tr>
<tr><td>Director of Personnel and Business Administration</td><td> <span class="smcap">W. W. Stockberger.</span></td></tr>
<tr><td>Director of Information</td><td> <span class="smcap">M. S. Eisenhower.</span></td></tr>
<tr><td>Solicitor</td><td> <span class="smcap">E. L. Marshall.</span></td></tr>
<tr><td>Bureau of Agricultural Economics</td><td> <span class="smcap">Nils A. Olsen</span>, <i>Chief</i>.</td></tr>
<tr><td>Bureau of Agricultural Engineering</td><td> <span class="smcap">S. H. McCrory</span>, <i>Chief</i>.</td></tr>
<tr><td>Bureau of Animal Industry</td><td> <span class="smcap">John R. Mohler</span>, <i>Chief</i>.</td></tr>
<tr><td>Bureau of Biological Survey</td><td> <span class="smcap">Paul G. Redington</span>, <i>Chief</i>.</td></tr>
<tr><td>Bureau of Chemistry and Soils</td><td> <span class="smcap">H. G. Knight</span>, <i>Chief</i>.</td></tr>
<tr><td>Office of Cooperative Extension Work</td><td> <span class="smcap">C. B. Smith</span>, <i>Chief</i>.</td></tr>
<tr><td>Bureau of Dairy Industry</td><td> <span class="smcap">O. E. Reed</span>, <i>Chief</i>.</td></tr>
<tr><td>Bureau of Entomology</td><td> <span class="smcap">C. L. Marlatt</span>, <i>Chief</i>.</td></tr>
<tr><td>Office of Experiment Stations</td><td> <span class="smcap">James T. Jardine</span>, <i>Chief</i>.</td></tr>
<tr><td>Food and Drug Administration</td><td> <span class="smcap">Walter G. Campbell</span>, <i>Director of Regulatory Work, in Charge.</i></td></tr>
<tr><td>Forest Service</td><td> <span class="smcap">R. Y. Stuart</span>, <i>Chief</i>.</td></tr>
<tr><td>Grain Futures Administration</td><td> <span class="smcap">J. W. T. Duvel</span>, <i>Chief</i>.</td></tr>
<tr><td>Bureau of Home Economics</td><td> <span class="smcap">Louise Stanley</span>, <i>Chief</i>.</td></tr>
<tr><td>Library</td><td> <span class="smcap">Claribel R. Barnett</span>, <i>Librarian</i>.</td></tr>
<tr><td>Bureau of Plant Industry</td><td> <span class="smcap">William A. Taylor</span>, <i>Chief</i>.</td></tr>
<tr><td>Bureau of Plant Quarantine</td><td> <span class="smcap">Lee A. Strong</span>, <i>Chief</i>.</td></tr>
<tr><td>Bureau of Public Roads</td><td> <span class="smcap">Thomas H. MacDonald</span>, <i>Chief</i>.</td></tr>
<tr><td>Weather Bureau</td><td> <span class="smcap">Charles F. Marvin</span>, <i>Chief</i>.</td></tr>
</table>

<p class="center">U. S. GOVERNMENT PRINTING OFFICE: 1938<br />
For sale by the Superintendent of Documents, Washington, D. C. Price 5 cents</p>
<hr />

<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1] </span></a> <i>Musca domestica</i> L.</p></div>
<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2] </span></a> <i>Stomoxys calcitrans</i> L.</p></div>
<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3] </span></a> <i>Pollenia rudis</i> Fab.</p></div>
<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4] </span></a> <i>Calliphora erythrocephala</i> Meig.</p></div>
<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5] </span></a> <i>Phormia regina</i> Meig. and <i>P. terrae-novae</i> Desv.</p></div>
<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6] </span></a> <i>Lucilia caesar</i> L., <i>L. sericata</i> Meig., and other species of the genus.</p></div>
<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7] </span></a> <i>Fannia canicularis</i> L.</p></div>
<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8] </span></a> <i>Drosophila ampelophila</i> Loew.</p></div>
<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9] </span></a> 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.</p></div>
<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10] </span></a> <i>Veratrum viride</i> or <i>V. aloum.</i></p></div>
<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11] </span></a> Department Bulletin 118, U. S. Department of Agriculture, p. 25.</p></div>
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