HOUSE RATS AND MICE

DAVID E. LANTZ

Assistant Biologist

FARMERS’ BULLETIN 896

UNITED STATES DEPARTMENT OF AGRICULTURE

Contribution from the Bureau of Biological Survey

E. W. NELSON, Chief

Washington, D. C. October, 1917

Show this bulletin to a neighbor. Additional copies may be
obtained free from the Division of Publications, United States
Department of Agriculture

WASHINGTON: GOVERNMENT PRINTING OFFICE: 1917

The rat is the worst animal pest in the world.

From its home among filth it visits dwellings and
storerooms to pollute and destroy human food.

It carries bubonic plague and many other diseases
fatal to man and has been responsible for more untimely
deaths among human beings than all the wars
of history.

In the United States rats and mice each year destroy
crops and other property valued at over $200,000,000.

This destruction is equivalent to the gross earnings
of an army of over 200,000 men.

On many a farm, if the grain eaten and wasted by
rats and mice could be sold, the proceeds would more
than pay all the farmer's taxes.

The common brown rat breeds 6 to 10 times a
year and produces an average of 10 young at a litter.
Young females breed when only three or four months
old.

At this rate a pair of rats, breeding uninterruptedly
and without deaths, would at the end of three years
(18 generations) be increased to 359,709,482 individuals.

For centuries the world has been fighting rats
without organization and at the same time has been
feeding them and building for them fortresses for
concealment. If we are to fight them on equal terms
we must deny them food and hiding places. We must
organize and unite to rid communities of these pests.
The time to begin is now.

HOUSE RATS AND MICE.

CONTENTS.

•  Page.


• Destructive habits
  3


• Protection of food and other stores
  5
  
  
  
  • Rat-proof building
    5
  
  
  • Keeping food from rats and mice
    9
  
  


• Destroying rats and mice
  11
  
  
  
  • Traps
    11
  
  
  • Poisons
    15
  
  
  • Domestic animals
    18
  
  
  • Fumigation
    18
  
  
  • Rat viruses
    19
  
  
  • Natural enemies
    20
  
  


• Organized efforts to destroy rats
  20
  
  
  
  • Community efforts
    21
  
  
  • State and national aid
    21
  
  


• Important repressive measures
  23

DESTRUCTIVE HABITS OF HOUSE RATS AND MICE.

Losses from depredations of house rats amount to many millions
of dollars yearly—to more, in fact, than those from all other
injurious mammals combined. The common house mouse[1] and the
brown rat[2] (fig. 1), too familiar to need description, are pests in
nearly all parts of the country; while two other kinds of house rats,
known as the black rat[3] and the roof rat,[4] are found within our
borders.

Fig. 1.—Brown rat.

Of these four introduced species—for none is native to America—the
brown rat is the most destructive, and, except the mouse, the most
numerous and most widely distributed. Brought to America just[Pg 4]
before the Revolution, it has supplanted and nearly exterminated
its less robust relative the black rat; and in spite of the constant warfare
of man has extended its range and steadily increased in numbers.
Its dominance is due to its great fecundity and its ability to adapt
itself to all sorts of surroundings. It breeds (in the middle part of
the United States) six or more times a year and produces from 6 to
20 young (average 10) in a litter. Females breed when only 3 or 4
months old. Thus a pair, breeding uninterruptedly and without
deaths, could in three years (18 generations) produce a posterity of
359,709,480 individuals. Mice and the black and roof rats produce
smaller litters, but the period of gestation, about 21 days, and the
number of litters are the same for all.

Rats and mice are practically omnivorous, feeding upon all kinds
of animal and vegetable matter. The brown rat makes its home in
the open field, the hedge row, and the river bank, as well as in stone
walls, piers, and all kinds of buildings. It destroys grains when
newly planted, while growing, and in the shock, stack, mow, crib,
granary, mill, elevator, or ship's hold, and also in the bin and feed
trough. It invades store and warehouse and destroys furs, laces,
silks, carpets, leather goods, and groceries. It attacks fruits, vegetables,
and meats in the markets, and destroys by pollution ten times
as much as it actually eats. It destroys eggs and young poultry, and
eats the eggs and young of song and game birds. It carries disease
germs from house to house and bubonic plague from city to city.
It causes disastrous conflagrations; floods houses by gnawing lead
water pipes; ruins artificial ponds and embankments by burrowing;
and damages foundations, floors, doors, and furnishings of dwellings.

Unlike the brown rat the black rat rarely migrates to the fields.
It has disappeared from most parts of the Northern States, but is
occasionally found in remote villages or farms. At our seaports it
frequently arrives on ships from abroad, but seldom becomes very
numerous. The roof rat is common in many parts of the South,
where it is a persistent pest in cane and rice fields. It maintains
itself against the brown rat partly because of its habit of living in
trees. The common house mouse by no means confines its activities
to the inside of buildings, but is often found in open fields, where its
depredations in shock and stack are well known.

Not only are mice and rats, especially the brown rat, a cause of
destruction and damage to property, but they are also a constant
menace to the health of man. It has been proved that they are the
chief means of perpetuating and transmitting bubonic plague and
that they play important rôles in conveying other diseases to human
beings. They are parasites, without redeeming characteristics, and
should everywhere be routed and destroyed.

PROTECTION OF FOOD AND OTHER STORES FROM RATS AND MICE.

Past attempts to exterminate rats and mice have failed, not so much
because of lack of effective means as because of the neglect of necessary
precautions and the absence of concerted endeavors. We have
rendered our work abortive by continuing to provide subsistence and
hiding places for the animals. If these advantages are denied, persistent
and general use of the usual methods of destruction will prove
far more successful.

RAT-PROOF BUILDING.

First in importance, as a measure of rat repression, is the exclusion
of the animals from places where they find food and safe retreats for
rearing their young.

The best way to keep rats from buildings, whether in city or in
country, is to use cement in construction. As the advantages of this
material are coming to be generally understood, its use is rapidly extending
to all kinds of buildings. The processes of mixing and laying
this material require little skill or special knowledge, and
workmen of ordinary intelligence can successfully follow the plain
directions contained in handbooks of cement construction.[5]

Many modern public buildings are so constructed that rats can
find no lodgment in the walls or foundations, and yet in a few years,
through negligence, such buildings often become infested with the
pests. Sometimes drain pipes are left uncovered for hours at a time.
Often outer doors, especially those opening on alleys, are left ajar.
A common mistake is failure to screen basement windows which must
be opened for ventilation. However the intruders are admitted, when
once inside they intrench themselves behind furniture or stores, and
are difficult to dislodge. The addition of inner doors to vestibules is
an important precaution against rats. The lower edge of outer doors
to public buildings, especially markets, should be reinforced with
light metal plates to prevent the animals from gnawing through.
Any opening left around water, steam, or gas pipes, where they go
through walls, should be closed carefully with concrete to the full
depth of the wall.

Dwellings.—In constructing dwelling houses the additional cost of
making the foundations rat-proof is slight compared with the advantages.
The cellar walls should have concrete footings, and the
walls themselves should be laid in cement mortar. The cellar floor
should be of medium rather than lean concrete. Even old cellars
may be made rat-proof at comparatively small expense. Rat holes
may be permanently closed with a mixture of cement, sand, and
broken glass, or sharp bits of crockery or stone.

[Pg 6]
On a foundation like the one described above, the walls of a wooden
dwelling also may be made rat-proof. The space between the sheathing
and lath, to the height of about a foot, should be filled with concrete.
Rats can not then gain access to the walls, and can enter the
dwelling only through doors or windows. Screening all basement
and cellar windows with wire netting is a most necessary precaution.

Old buildings in cities.—Aside from old dwellings, the chief refuges
for rats in cities are sewers, wharves, stables, and outbuildings.
Modern sewers are used by the animals merely as highways and not as
abodes, but old-fashioned brick sewers often afford nesting crannies.

Fig. 2.—Rat-proofing a frame dwelling
by concrete side wall (United States Public Health Service, New Orleans,
La., 1914).

Wharves, stables, and outbuildings in cities should be so built as to
exclude rats. Cement is the chief means to this end. Old tumble-down
buildings and wharves should not be tolerated in any city.
(See fig. 2.)

In both city and country, wooden floors of sidewalks, areas, and
porches are commonly laid upon timbers resting on the ground.
Under such floors rats have a safe retreat from nearly all enemies.
The conditions can be remedied in towns by municipal action requiring
that these floors be replaced by others made of cement. Areas or
walks made of brick are often undermined by rats and may become
as objectionable as those of wood. Wooden floors of porches should
always be well above the ground.

[Pg 7]
Farm buildings.—Granaries, corncribs, and poultry houses may be
made rat-proof by a liberal use of cement in the foundations and
floors; or the floors may be of wood resting upon concrete. Objection
has been urged against concrete floors for horses, cattle, and poultry,
because the material is too good a conductor of heat, and the health
of the animals suffers from contact with these floors. In poultry
houses, dry soil or sand may be used as a covering for the cement
floor, and in stables a wooden floor resting on concrete is just as satisfactory
so far as the exclusion of rats is concerned.

The common practice of setting corncribs on posts with inverted
pans at the top often fails to exclude rats, because the posts are not
high enough to place the lower cracks of the structure beyond reach
of the animals. As rats are excellent jumpers, the posts should be
tall enough to prevent the animals from obtaining a foothold at any
place within 3 feet of the ground. A crib built in this way, however,
is not very satisfactory.

For a rat-proof crib a well-drained site should be chosen. The
outer walls, laid in cement, should be sunk about 20 inches into the
ground. The space within the walls should be grouted thoroughly
with cement and broken stone and finished with rich concrete for a
floor. Upon this the structure may be built. Even the walls of the
crib may be of concrete. Corn will not mold in contact with them,
provided there is good ventilation and the roof is water-tight.

However, there are cheaper ways of excluding rats from either
new or old corncribs. Rats, mice, and sparrows may be kept out
effectually by the use of either an inner or an outer covering of galvanized-wire
netting of half-inch mesh and heavy enough to resist
the teeth of the rats. The netting in common use in screening cellar
windows is suitable for covering or lining cribs. As rats can climb
the netting, the entire structure must be screened, or, if sparrows are
not to be excluded, the wire netting may be carried up about 3
feet from the ground, and above this a belt of sheet metal about a
foot in width may be tacked to the outside of the building.

Complete working drawings for the practical rat-proof corncrib
shown in figures 3 and 4 may be obtained from the Office of Public
Roads and Rural Engineering of the department.

Buildings for storing foodstuffs.—Whenever possible, stores of food
for man or beast should be placed only in buildings of rat-proof
construction, guarded against rodents by having all windows near
the ground and all other possible means of entrance screened with
netting made of No. 18 or No. 20 wire and of ¼-inch mesh. Entrance
doors should fit closely, should have the lower edges protected by
wide strips of metal, and should have springs attached, to insure that
they shall not be left open. Before being used for housing stores,
the building should be inspected as to the manner in which water,
[Pg 8]
steam, or gas pipes go through the walls, and any openings found
around such pipes should be closed with concrete.

Fig. 3.—Perspective of rat-proof
corncrib, showing concrete foundation by dotted lines; also
belt of metal.

If rat-proof buildings are not available, it is possible, by the use
of concrete in basements and the other precautions just mentioned, to
make an ordinary building practically safe for food storage.

When it is necessary to erect temporary wooden structures to hold
forage, grain, or food supplies for army camps, the floors of such
buildings should not be in contact with the ground, but elevated, the
sills having a foot or more of clear space below them. Smooth posts
rising 2 or 3 feet above the ground may be used for foundations,
and the floor itself may be protected below by wire netting or sheet
metal at all places where rats could gain a foothold. Care should be
taken to have the floors as tight as possible, for it is chiefly scattered
grain and fragments of food about a camp that attract rats.

Rat-proofing by elevation.—The United States Public Health Service
reports that in its campaigns against bubonic plague in San
Francisco (1907) and New Orleans (1914) many plague rats were
found under the floors of wooden houses resting on the ground.
These buildings were made rat-proof by elevation, and no case of
either human or rodent plague occurred in any house after the
change. Placing them on smooth posts 18 inches above the ground,
with the space beneath the floor entirely open, left no hiding place
for rats.

This plan is adapted to small dwellings throughout the South, and
to small summer homes, temporary structures, and small farm buildings
everywhere. Wherever rats might obtain a foothold on the
top of the post they may be prevented from gnawing the adjacent
wood by tacking metal plates or pieces of wire netting to floor or sill.

KEEPING FOOD FROM RATS AND MICE.

The effect of an abundance of food on the breeding of rodents
should be kept in mind. Well-fed rats mature quickly, breed often,
and have large litters. Poorly fed rats, on the contrary, reproduce
less frequently and have smaller litters. In addition, scarcity of food
makes measures for destroying the animals far more effective.

Merchandise in stores.—In all parts of the country there is a serious
economic drain in the destruction by rats and mice of merchandise
held for sale by dealers. Not only foodstuffs and forage, but textiles,
clothing, and leather goods are often ruined. This loss is due mainly
to the faulty buildings in which the stores are kept. Often it would
be a measure of economy to tear down the old structures and replace
them by new ones. However, even the old buildings may often be
repaired so as to make them practically rat-proof; and foodstuffs, as
flour, seeds, and meats, may always be protected in wire cages at
slight expense. The public should be protected from insanitary
stores by a system of rigid inspection.

Fig. 4.—Floor
plan of rat-proof corncrib shown in figure 3.

Household supplies.—Similar care should be exercised in the home to
protect household supplies from mice and rats. Little progress in
ridding the premises of these animals can be made so long as they
have access to supplies of food. Cellars, kitchens, and pantries often
furnish subsistence not only to rats that inhabit the dwelling, but to
many that come from outside. Food supplies may always be kept
from rats and mice if placed in inexpensive rat-proof containers
covered with wire netting. Sometimes all that is needed to prevent
[Pg 10]
serious waste is the application of concrete to holes in the basement
wall or the slight repair of a defective part of the building.

Produce in transit.—Much loss of fruits, vegetables, and other produce
occurs in transit by rail and on ships. Most of the damage is
done at wharves and in railway stations, but there is also considerable
in ships' holds, especially to perishable produce brought from warm
latitudes. Much of this may be prevented by the use of rat-proof
cages at the docks, by the careful fumigation of seagoing vessels at
the end of each voyage, and by the frequent fumigation of vessels in
coastwise trade; but still more by replacing old and decrepit wharves
and station platforms with modern ones built of concrete.

Where cargoes are being loaded or unloaded at wharves or depots,
food liable to attack by rats may be temporarily safeguarded by being
placed in rat-proof cages, or pounds, constructed of wire netting.
Wooden boxes containing reserve food held in depots for a considerable
time or intended for shipment by sea may be made rat-proof by
light coverings of metal along the angles. This plan has long been in
use to protect naval stores on ships and in warehouses. It is based
on the fact that rats do not gnaw the plane surfaces of hard materials,
but attack doors, furniture, and boxes at the angles only.

Packing houses.—Packing houses and abattoirs are often sources
from which rats secure subsistence, especially where meats are prepared
for market in old buildings. In old-style cooling rooms with
double walls of wood and sawdust insulation, always a source of
annoyance because of rat infestation, the utmost vigilance is required
to prevent serious loss of meat products. On the other hand, packing
houses with modern construction and sanitary devices have no trouble
from rats or mice.

Garbage and waste.—Since much of the food of rats consists of
garbage and other waste materials, it is not enough to bar the animals
from markets, granaries, warehouses, and private food stores. Garbage
and offal of all kinds must be so disposed of that rats can not
obtain them.

In cities and towns an efficient system of garbage collection and
disposal should be established by ordinances. Waste from markets,
hotels, cafés and households should be collected in covered metal
receptacles and frequently emptied. Garbage should never be
dumped in or near towns, but should be utilized or promptly destroyed
by fire.

Rats find abundant food in country slaughterhouses; reform in the
management of these is badly needed. Such places are centers of rat
propagation. It is a common practice to leave offal of slaughtered
animals to be eaten by rats and swine, and this is the chief means of
perpetuating trichinæ in pork. The law should require that offal be
promptly cremated or otherwise disposed of. Country
slaughter[Pg 11]houses
should be as cleanly and as constantly inspected as abattoirs.

Another important source of rat food is found in remnants of lunches left
by employees in factories, stores, and public buildings. This food, which
alone is sufficient to attract and sustain a small army of rats, is commonly left
in waste baskets or other open receptacles. Strictly enforced rules requiring
all remnants of food to be deposited in covered metal vessels would make trapping
far more effective.

Military training camps, unless subjected to rigid
discipline in the matter of disposal of garbage and waste, soon
become centers of rat infestation. Waste from camps, deposited in
covered metal cans and collected daily, should be removed far from
the camp itself and either burned or utilized in approved modern
ways.

DESTROYING RATS AND MICE.

The Biological Survey has made numerous laboratory and field
experiments with various agencies for destroying rats and mice.
The results form the chief basis for the following recommendations:

TRAPS.

Owing to their cunning, it is not always easy to clear rats from
premises by trapping; if food is abundant, it is impossible. A few
adults refuse to enter the most innocent-looking trap. And yet trapping,
if persistently followed, is one of the most effective ways of
destroying the animals.

Fig. 5.—Guillotine
trap made entirely of metal.

Guillotine trap.—For general use the improved modern traps with a
wire fall released by a baited trigger and driven by a coiled spring
have marked advantages over the old forms, and many of them may
be used at the same time. These traps, sometimes called "guillotine"
traps, are of many designs, but the more simply constructed are preferable.
Probably those made entirely of metal are the best, as they
[Pg 12]
are more durable. Traps with tin or sheet-metal bases are not recommended.

Guillotine traps of the type shown in figure 5 should be baited
with small pieces of Vienna sausage (Wienerwurst) or fried bacon.
A small section of an ear of corn is an excellent bait if other grain
is not present. The trigger wire should be bent inward to bring
the bait into proper position for the fall to strike the rat in the neck,
as shown in figure 6.

Other excellent baits for rats and mice are oatmeal, toasted cheese,
toasted bread (buttered), fish, fish offal, fresh liver, raw meat, pine
nuts, apples, carrots, and corn, and sunflower, squash, or pumpkin
seeds. Broken fresh eggs are good bait at all seasons, and ripe
tomatoes, green cucumbers, and other fresh vegetables are very
tempting to the animals in winter. When seed, grain, or meal is
used with a guillotine trap, it is put on the trigger plate, or the trigger
wire may be bent outward and the bait placed directly under it.

Oatmeal (rolled oats) is recommended as a bait for guillotine traps
made with wooden base and trigger plate (fig. 7). These traps are
especially convenient to use on ledges or other narrow rat runs or
at the openings of rat burrows. They are often used without bait.

Fig. 6.—Method
of baiting guillotine trap.

A common mistake in trapping for rats and mice is to use only
one or two traps when dozens are needed. For a large establishment
hundreds of traps may be used to advantage, and a dozen is none too
many for an ordinary barn or dwelling infested with rats. House
mice are less suspicious than rats and are much more easily trapped.
[Pg 13]
Small guillotine traps baited with oatmeal will soon rid
an ordinary dwelling of the smaller pests.

Fig. 7.—Guillotine
trap with wooden base and trigger plate.

Cage trap.—When rats are abundant, the large French
wire cage traps may be used to advantage. They should be made
of stiff wire, well reinforced. Many of those sold in stores are useless,
because a full-grown rat can bend the light wires apart and so escape.

Cage traps may be baited and left open for several nights until the
rats are accustomed to enter them to obtain food. They should then
be closed and freshly baited, when a larger catch may be expected,
especially of young rats (fig. 8). As many as 25, and even more,
partly grown rats have been taken at a time in one of these traps.
It is better to cover the trap than to leave it exposed. A short board
should be laid on the trap and an old cloth or bag or a bunch of hay
or straw thrown carelessly over the top. Often the trap may be
placed with the entrance opposite a rat hole and fitting it so closely
that rats can not pass through without entering the trap. If a single
rat is caught it may be left in the trap as a decoy to others.

Notwithstanding the fact that sometimes a large number of rats
may be taken at a time in cage traps, a few good guillotine traps
intelligently used will prove more effective in the long run.

Fig. 8.—Cage
trap with catch of rats.

Figure-4 trigger trap.—The old-fashioned box trap set with a figure-4
trigger is sometimes useful to secure a wise old rat that refuses
to be enticed into a modern trap. Better still is a simple
deadfall[Pg 14]—a
flat stone or a heavy plank—supported by a figure-4 trigger. An
old rat will go under such a contrivance to feed without fear.

Steel trap.—The ordinary steel trap (No. 0 or 1) may sometimes be
satisfactorily employed to capture a rat. The animal is usually
caught by the foot, and its squealing has a tendency to frighten other
rats. The trap may be set in a shallow pan or box and covered with
bran or oats, care being taken to have the space under the trigger pan free
of grain. This may be done by placing a very little cotton under the trigger
and setting as lightly as possible. In a narrow run or at the mouth of a burrow
a steel trap unbaited and covered with very light cloth or tissue paper is
often effective.

The best bait usually is food of a kind that the rats and mice do not
get in the vicinity. In a meat market, vegetables or grain should
be used; in a feed store, meat. As far as possible food other than
the bait should be inaccessible while trapping is in progress. The
bait should be kept fresh and attractive, and the kind changed when
necessary. Baits and traps should be handled as little as possible.

Fig. 9.—Barrel
trap: 1, With stiff paper cover; 2, with hinged barrel cover;
a, stop; b, baits.

Barrel trap.—About 60 years ago a writer in the Cornhill Magazine
gave details of a trap, by means of which it was claimed
that 3,000 rats were caught in a warehouse in a single night. The
plan involved tolling the rats to the place
and feeding them for several nights on the tops of barrels covered
with coarse brown paper. Afterwards a cross was cut in the paper,
so that the rats fell into the barrel (fig. 9 (1)). Many variations of
the plan, but few improvements upon it, have been suggested by agricultural
writers since that time. Reports are frequently made of large
catches of rats by means of a barrel fitted with a light cover of wood,
hinged on a rod so as to turn with the weight of a rat (fig. 9 (2)).

Fig. 10.—Pit trap.
aa, Rat run; bb, cover; cc, position of weights; dd, rods on which covers
turn.

[Pg 15]
Pit trap.—A modification of the barrel trap is the pit trap (fig. 10).
This consists of a stout narrow box sunk in the ground so that the
top is level with the rat run. It is fixed with a cover of light wood
or metal in two sections, the sections fitting nicely inside the box
and working independently. They turn on rods, to which they are
fastened. They are weighted near the ends of the box and so adjusted
that they swing easily. An animal stepping upon the cover
beyond the rods is precipitated into the box, while the cover immediately
swings back to its place. Besides rats, the trap is well
adapted to capture larger animals, as minks, raccoons, opossums, and
cats. It is especially useful to protect poultry yards, game preserves,
and the like. The trap should be placed along the fence outside the
yard, and behind a shelter of boards or brush that leans against the
fence.

Fence and battue.—In the rice fields of the Far East the natives
build numerous piles of brush and rice straw, and leave them for
several days until many rats have taken shelter in them. A portable
bamboo inclosure several feet in height is then set up around each
pile in succession and the straw and brush are thrown out over the
top, while dogs and men kill the trapped rodents. Large numbers
are destroyed in this way, and the plan with modifications may be
utilized in America with satisfactory results. A wire netting of fine
mesh may be used for the inclosure. The scheme is applicable at the
removal of grain, straw, or haystacks, as well as brush piles.

In a large barn near Washington, a few years ago, piles of unhusked
corn were left in the loft and were soon infested with rats.
A wooden pen was set down surrounding the piles in turn and the
corn thrown out until dogs were able to get at the rats. In this way
several men and dogs killed 500 rats in a single day.

POISONS.

While the use of poison is the best and quickest way to get rid of
rats and mice, the odor from the dead animals makes the method impracticable
in occupied houses. Poisons may be effectively used in
barns, stables, sheds, cribs, and other outbuildings.

Caution.—In the United States there are few laws which prohibit
the laying of poisons on lands owned or controlled by the poisoner.
Hence it is all the more necessary to exercise extreme caution to
prevent accidents. In several States notice of intention to lay poison
must be given to persons living in the neighborhood. Poison for
rats should never be placed in open or unsheltered places. This
applies particularly to strychnin or arsenic on meat. Packages containing
poisons should always bear a warning label and should not
be kept where children might reach them.

[Pg 16]
Among the principal poisons that have been recommended for
killing rats and mice are barium carbonate, strychnin, arsenic, phosphorus,
and squills.

Barium carbonate.—One of the cheapest and most effective poisons
for rats and mice is barium carbonate. This mineral has the advantage
of being without taste or smell. It has a corrosive action on the
mucous lining of the stomach and is dangerous to larger animals if
taken in sufficient quantity. In the small doses fed to rats and mice
it would be harmless to domestic animals. Its action upon rats is
slow, and if exit is possible the animals usually leave the premises in
search of water. For this reason the poison may frequently, though
not always, be used in houses without disagreeable consequences.

Barium carbonate may be fed in the form of dough composed of
four parts of meal or flour and one part of the mineral. A more
convenient bait is ordinary oatmeal with about one-eighth of its bulk
of the mineral, mixed with water into a stiff dough. A third plan is
to spread the barium carbonate upon fish, toasted bread (moistened),
or ordinary bread and butter. The prepared bait should be placed in
rat runs, about a teaspoonful at a place. If a single application of
the poison fails to kill or drive away all rats from the premises, it
should be repeated with a change of bait.

Strychnin.—Strychnin is too rapid in action to make its use for
rats desirable in houses, but elsewhere it may be employed effectively.
Strychnia sulphate is the best form to use. The dry crystals may be
inserted in small pieces of raw meat, Vienna sausage, or toasted
cheese, and these placed in rat runs or burrows; or oatmeal may be
moistened with a strychnin sirup and small quantities laid in the
same way.

Strychnin sirup is prepared as follows: Dissolve a half ounce of
strychnia sulphate in a pint of boiling water; add a pint of thick
sugar sirup and stir thoroughly. A smaller quantity may be prepared
with a proportional quantity of water and sirup. In preparing
the bait it is necessary to moisten all the oatmeal with the sirup.
Wheat and corn are excellent alternative baits. The grain should
be soaked overnight in the strychnin sirup.

Arsenic.—Arsenic is probably the most popular of the rat poisons,
owing to its cheapness, yet our experiments prove that, measured
by the results obtained, arsenic is dearer than strychnin. Besides,
arsenic is extremely variable in its effect upon rats, and if the animals
survive a first dose it is very difficult to induce them to take
another.

Powdered white arsenic (arsenious acid) may be fed to rats in
almost any of the baits mentioned under barium carbonate and
strychnin. It has been used successfully when rubbed into fresh
fish or spread on buttered toast. Another method is to mix twelve
[Pg 17]
parts by weight of corn meal and one part of arsenic with whites of
eggs into a stiff dough.

An old formula for poisoning rats and mice with arsenic is the
following, adapted from an English source:

Take a pound of oatmeal, a pound of coarse brown sugar, and a
spoonful of arsenic. Mix well together and put the composition into
an earthen jar. Put a tablespoonful at a place in runs frequented
by rats.

Phosphorus.—For poisoning rats and mice, phosphorus is used
almost as commonly as arsenic, and undoubtedly it is effective when
given in an attractive bait. The phosphorus paste of the drug
stores is usually dissolved yellow phosphorus, mixed with glucose or
other substances. The proportion of phosphorus varies from one-fourth
of 1 per cent to 4 per cent. The first amount is too small
to be always effective and the last is dangerously inflammable. When
homemade preparations of phosphorus are used there is much danger
of burning the person or of setting fire to crops or buildings.
In the Western States many fires have resulted from putting out
homemade phosphorus poisons for ground squirrels, and entire fields
of ripe grain have been destroyed in this way. Even with commercial
pastes the action of sun and rain changes the phosphorus
and leaches out the glucose until a highly inflammable residue is left.

It is often claimed that phosphorus eaten by rats or mice dries up
or mummifies the body so that no odor results. The statement has
no foundation in fact. No known poison will prevent decomposition
of the body of an animal that died from its effects. Equally misleading
is the statement that rats poisoned with phosphorus do not
die on the premises. Owing to its slower operation, no doubt a
larger portion escape into the open before dying than when strychnin
is used.

The Biological Survey does not recommend the use of phosphorus
as a poison for rodents.

Squills.—The squill, or sea leek,[6] is a favorite rat poison in many
parts of Europe and is well worthy of trial in America. It is rapid
and very deadly in its action, and rats seem to eat it readily. The
poison is used in several ways. Two ounces of dry squills, powdered,
may be thoroughly mixed with eight ounces of toasted cheese or of
butter and meal and put out in runs of rats or mice. Another formula
recommends two parts of squills to three parts of finely
chopped bacon, mixed with meal enough to make it cohere. This is
baked in small cakes.

Poison in poultry houses.—For poisoning rats in buildings and yards
occupied by poultry the following method is recommended: Two
[Pg 18]
wooden boxes should be used, one considerably larger than the other
and each having one or more holes in the sides large enough to
admit rats. The poisoned bait should be placed on the bottom and
near the middle of the smaller box, and the larger box should then
be inverted over it. Rats thus have free access to the bait, but fowls
are excluded.

DOMESTIC ANIMALS.

Among domestic animals employed to kill rats are the dog, the
cat, and the ferret.

Dogs.—The value of dogs as ratters can not be appreciated by persons
who have had no experience with a trained animal. The ordinary
cur and the larger breeds of dogs seldom develop the necessary
qualities for ratters. Small Irish, Scotch, and fox terriers, when
properly trained, are superior to other breeds and under favorable
circumstances may be relied upon to keep the farm premises reasonably
free from rats.

Cats.—However valuable cats may be as mousers, few learn to catch
rats. The ordinary house cat is too well fed and consequently too
lazy to undertake the capture of an animal as formidable as the
brown rat. Birds and mice are much more to its liking. Cats that
are fearless of rats, however, and have learned to hunt and destroy
them are often very useful about stables and warehouses. They
should be lightly fed, chiefly on milk. A little sulphur in the milk at
intervals is a corrective against the bad effects of a constant rat or
mouse diet. Cats often die from eating these rodents.

Ferrets.—Tame ferrets, like weasels, are inveterate foes of rats, and
can follow the rodents into their retreats. Under favorable circumstances
they are useful aids to the rat catcher, but their value is
greatly overestimated. For effective work they require experienced
handling and the additional services of a dog or two. Dogs and
ferrets must be thoroughly accustomed to each other, and the former
must be quiet and steady instead of noisy and excitable. The ferret
is used only to bolt the rats, which are killed by the dogs. If unmuzzled
ferrets are sent into rat retreats, they are apt to make a kill
and then lie up after sucking the blood of their victim. Sometimes
they remain for hours in the burrows or escape by other exits and
are lost. There is danger that these lost ferrets may adapt themselves
to wild conditions and become a pest by preying upon poultry
and birds.

FUMIGATION.

Rats may be destroyed in their burrows in the fields and along
river banks, levees, and dikes by carbon bisulphid.[7] A wad of
cot[Pg 19]ton
or other absorbent material is saturated with the liquid and
then pushed into the burrow, the opening being packed with earth to
prevent the escape of the gas. All animals in the burrow are asphyxiated.
Fumigation in buildings is not so satisfactory, because it is
difficult to confine the gases. Moreover, when effective, the odor
from the dead rats is highly objectionable in occupied buildings.

Chlorin, carbon monoxid, sulphur dioxid, and hydrocyanic acid
are the gases most used for destroying rats and mice in sheds, warehouses,
and stores. Each is effective if the gas can be confined and
made to reach the retreats of the animals. Owing to the great danger
from fire incident to burning charcoal or sulphur in open pans, a
special furnace provided with means for forcing the gas into the compartments
of vessels or buildings is generally employed.

Hydrocyanic-acid gas is effective in destroying all animal life in
buildings. It has been successfully used to free elevators and warehouses
of rats, mice, and insects. However, it is so dangerous to
human life that the novice should not attempt fumigation with it,
except under careful instructions. Directions for preparing and
using the gas may be found in a publication entitled Hydrocyanic-acid
Gas against Household Insects, by Dr. L. O. Howard and
Charles H. Popenoe.[8]

Carbon monoxid is rather dangerous, as its presence in the hold of
a vessel or other compartment is not manifest to the senses, and fatal
accidents have occurred during its employment to fumigate vessels.

Chlorin gas has a strong bleaching action upon textile fabrics, and
for this reason can not be used in many situations.

Sulphur dioxid also has a bleaching effect upon textiles, but less
marked than that of chlorin, and ordinarily it is not noticeable with
the small percentage of the gas it is necessary to use. On the whole,
this gas has many advantages as a fumigator and disinfectant. It is
used also as a fire extinguisher on board vessels. Special furnaces for
generating the gas and forcing it into the compartments of ships and
buildings are on the market, and many steamships and docks are
now fitted with the necessary apparatus.

RAT VIRUSES.

Several microorganisms, or bacteria, found originally in diseased
rats or mice, have been exploited for destroying rats. A number of
these so-called rat viruses are on the American market. The Biological
Survey, the Bureau of Animal Industry, and the United States
Public Health Service have made careful investigations and practical
tests of these viruses, mostly with negative results. The cultures
tested by the Biological Survey have not proved satisfactory.

The chief defects to be overcome before the cultures can be recommended
for general use are:

[Pg 20]
1. The virulence is not great enough to kill a sufficiently high percentage
of rats that eat food containing the microorganisms.

2. The virulence decreases with the age of the cultures. They deteriorate
in warm weather and in bright sunlight.

3. The diseases resulting from the microorganisms are not contagious
and do not spread by contact of diseased with healthy
animals.

4. The comparative cost of the cultures is too great for general use.
Since they have no advantages over the common poisons, except that
they are usually harmless to man and other animals, they should be
equally cheap; but their actual cost is much greater. Moreover, considering
the skill and care necessary in their preparation, it is doubtful
if the cost can be greatly reduced.

The Department of Agriculture, therefore, does not prepare, use,
or recommend the use of rat viruses.

NATURAL ENEMIES OF RATS AND MICE.

Among the natural enemies of rats and mice are the larger hawks
and owls, skunks, foxes, coyotes, weasels, minks, dogs, cats, and
ferrets.

Probably the greatest factor in the increase of rats, mice, and other
destructive rodents in the United States has been the persistent killing
off of the birds and mammals that prey upon them. Animals that
on the whole are decidedly beneficial, since they subsist upon harmful
insects and rodents, are habitually destroyed by some farmers and
sportsmen because they occasionally kill a chicken or a game bird.

The value of carnivorous mammals and the larger birds of prey in
destroying rats and mice should be more fully recognized, especially
by the farmer and the game preserver. Rats actually destroy more
poultry and game, both eggs and young chicks, than all the birds and
wild mammals combined; yet some of their enemies among our most
useful birds of prey and carnivorous mammals are persecuted almost
to the point of extinction. An enlightened public sentiment should
cause the repeal of all bounties on these animals and afford protection
to the majority of them.

ORGANIZED EFFORTS TO DESTROY RATS.

The necessity of cooperation and organization in the work of rat
destruction is of the utmost importance. To destroy all the animals
on the premises of a single farmer in a community has little permanent
value, since they are soon replaced from near-by farms. If,
however, the farmers of an entire township or county unite in efforts
to get rid of rats, much more lasting results may be attained. If continued
from year to year, such organized efforts are very effective.

COMMUNITY EFFORTS.

Cooperative efforts to destroy rats have taken various forms in
different localities. In cities, municipal employees have occasionally
been set at work hunting rats from their retreats, with at least temporary
benefit to the community. Thus, in 1904, at Folkestone, England,
a town of about 25,000 inhabitants, the corporation employees,
helped by dogs, in three days killed 1,645 rats.

Side hunts in which rats are the only animals that count in the
contest have sometimes been organized and successfully carried out.
At New Burlington, Ohio, a rat hunt took place some years ago in
which each of the two sides killed over 8,000 rats, the beaten party
serving a banquet to the winners.

There is danger that organized rat hunts will be followed by long
intervals of indifference and inaction. This may be prevented by
offering prizes covering a definite period of effort. Such prizes
accomplish more than municipal bounties, because they secure a
friendly rivalry which stimulates the contestants to do their utmost
to win.

In England and some of its colonies contests for prizes have been
organized to promote the destruction of the English, or house, sparrow,
but many of the so-called sparrow clubs are really sparrow and
rat clubs, for the destruction of both pests is the avowed object of
the organizations. A sparrow club in Kent, England, accomplished
the destruction of 28,000 sparrows and 16,000 rats in three seasons
by the annual expenditure of but £6 ($29.20) in prize money. Had
ordinary bounties been paid for this destruction, the tax on the community
would have been about £250 (over $1,200).

Many organizations already formed should be interested in destroying
rats. Boards of trade, civic societies, and citizens' associations
in towns and farmers' and women's clubs in rural communities
will find the subject of great importance. Women's municipal
leagues in several large cities already have taken up the matter.
The league in Baltimore recently secured appropriations of funds
for expenditure in fighting mosquitoes, flies, and rats. The league
in Boston during the past year, supported by voluntary contributions
for the purpose, made a highly creditable educational campaign
against rats. Boys' corn clubs, the troops of Boy Scouts, and
similar organizations could do excellent work in rat campaigns.

STATE AND NATIONAL AID.

To secure permanent results any general campaign for the elimination
of rats must aim at building the animals out of shelter and food.
Building reforms depend on municipal ordinances and legislative
[Pg 22]
enactments. The recent plague eradication work of the United
States Public Health Service in San Francisco, Seattle, New Orleans,
and at various places in Hawaii and Porto Rico required such ordinances
and laws as well as financial aid in prosecuting the work.
The campaign of Danish and Swedish organizations for the destruction
of rats had the help of governmental appropriations. The legislatures
of California, Texas, Indiana, and Hawaii have in recent
years passed laws or made appropriations to aid in rat riddance. It is
probable that well-organized efforts of communities would soon win
legislative support everywhere. Communities should not postpone
efforts, however, while waiting for legislative cooperation, but should
at once organize and begin repressive operations. Wherever health
is threatened the Public Health Service of the United States can cooperate,
and where crops and other products are endangered the
Bureau of Biological Survey of the Department of Agriculture is
ready to assist by advice and in demonstration of methods.

IMPORTANT REPRESSIVE MEASURES.

The measures needed for repressing and eliminating rats and mice
include the following:

1. The requirement that all new buildings erected shall be made
rat-proof under competent inspection.

2. That all existing rat-proof buildings shall be closed against rats
and mice by having all openings accessible to the animals, from
foundation to roof, closed or screened by door, window, grating, or
meshed wire netting.

3. That all buildings not of rat-proof construction shall be made so
by remodeling, by the use of materials that may not be pierced by
rats, or by elevation.

4. The protection of our native hawks, owls, and smaller predatory
mammals—the natural enemies of rats.

5. Greater cleanliness about markets, grocery stores, warehouses,
courts, alleys, stables, and vacant lots in cities and villages, and like
care on farms and suburban premises. This includes the storage of
waste and garbage in tightly covered vessels and the prompt disposal
of it each day.

6. Care in the construction of drains and sewers, so as not to provide
entrance and retreat for rats. Old brick sewers in cities should
be replaced by concrete or tile.

7. The early threshing and marketing of grains on farms, so that
stacks and mows shall not furnish harborage and food for rats.

8. Removal of outlying straw stacks and piles of trash or lumber
that harbor rats in fields and vacant lots.

[Pg 23]
9. The keeping of provisions, seed grain, and foodstuffs in rat-proof containers.

10. Keeping effective rat dogs, especially on farms and in city warehouses.

11. The systematic destruction of rats, whenever and wherever
possible, by (a) trapping, (b) poisoning, and (c) organized hunts.

12. The organization of clubs and other societies for systematic
warfare against rats.

PUBLICATIONS OF THE UNITED STATES DEPARTMENT OF AGRICULTURE
RELATING TO NOXIOUS MAMMALS.

AVAILABLE FOR FREE DISTRIBUTION.

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, GOVERNMENT PRINTING
OFFICE, WASHINGTON, D. C.