Chapter VII: Part 7

The large 19-inch French cage trap gives good results where rats are
plentiful. It should be made of stiff, heavy wire and well reenforced,
as a large, strong rat will force his head between the wires in a weak
trap and thus escape. Before setting, the lever on the trap should be
tested to see that it works properly. The trap should be placed on a
hard surface, with the rear end a little higher than the entrance, so
that the trap will close promptly. When setting the trap in the open
it should be fastened to a board on which about an inch of soft dirt
has been spread. Place the trap where the rat usually goes for food or
in a runway and disturb the surroundings as little as possible. It is
sometimes well to place the trap near where there is dripping water,
as the rats come there to drink. If the trap is set in hay or straw or
wood it should be covered (with the exception of the entrance) with
this material. When this is not possible it should be covered with a
piece of sacking or placed in a dark corner or beneath the floors.
When setting the traps in the sewer a dry place should be chosen.

The rat is more or less of an epicure, therefore the bait should be
changed at frequent intervals. Also he should be given food which he
is not in the habit of getting. For example: In a meat market
vegetables are the best bait, while in a location where vegetables are
plentiful fresh liver and fish heads, or a little grain, are best. The
following may be suggested as good bait to be used: Fish, fish heads,
raw meat, cheese, smoked fish, fresh liver, cooked corn beef, fried
bacon, pine nuts, apples, carrots, and corn. When trapping in chicken
yards a small chick or duckling is remarkably good. When a large
number of rats are caught in one trap, search for the female and leave
her alive in the trap, as she may call in the young or the males. The
bait should be fastened to the inner side of the top of the trap with
a piece of fine wire so that the first rat in can not force the bait
underneath the pan and thus prevent the entrance of other rats. A few
grains of barley should be scattered near the entrance of the trap and
a small piece of cheese or meat fastened to the pan with a piece of
wire. It is often well to touch the pan with a feather which has been
dipped in oil of anise or oil of rhodium. Before leaving the trap it
should be smoked with a piece of burning newspaper to kill the smell
of the human hands or the rats which have been in it. Do not handle
the trap after burning it out. When trapping in a neighborhood where
rats are known to exist the traps should not be moved for three or
four days unless they have rats in them, as it is well for the rats to
become accustomed to seeing them and thus careless about entering. It
is not wise to kill rats where they are caught, as the squealing may
frighten the other rats away.

SNAP TRAPS.

Snap or spring traps are best for use in houses and stores, with the
exception of fish and meat markets. Snap traps are best for use in
runways, beams, and shelves. It is sometimes well to disguise the trap
by covering its floor with a little sawdust or dirt. They should be
first tested to see that they work properly and that the staples are
secure. New traps should be smoked or stained to render them an
inconspicuous color.

The bait should consist of some firm material, such as fried bacon or
tough meat, and should be tied on so that the rat will be obliged to
pull on it and thus spring the trap. The trap should be placed in a
corner or close to the wall on a flat, hard surface, so that the rat
can not spring it with his tail or by walking on it.

BARREL TRAPS.

In warehouses and granaries large numbers of rats may frequently be
trapped by using a barrel or garbage can having a metal top which is
carefully balanced. Large pieces of strong cheese are placed in the
middle of the cover and a plank laid from the floor to the edge of the
barrel. The rat runs up the plank onto the smooth metallic lid which
tips and the rat is precipitated into the barrel.

In cities trapping is one of the most effective of the three methods
to slaughter rodents. The rat highways are easily discovered and in
them traps capture great numbers of the unwary. In the country one can
not so readily determine the rat highway. This difficulty diminishes
the effectiveness of trapping. To make up for what is thus lost
shooting has been resorted to with good results. In Honolulu, where a
vigorous campaign against rodents is being waged, a very large
proportion of the captured rats (_Mus rattus_ and _M. alexandrinus_)
have been shot from trees. In Contra Costa County, Cal., where ground
squirrels are being exterminated, it has been found that rodents
possess an instinctive suspicion of traps and that during the summer
months shooting is not only the most practical but also about the only
effective means of attacking them. Shotguns are the weapons to use. A
rifle requires the hunter to be a better shot than is ordinarily
obtainable for such work, and, furthermore, the danger from its longer
range and from ricocheting bullets menaces cattle and farm hands who
may be working in the vicinity. As to the shot and the powder charge
for shells hunters differ. It is a different problem for every
shotgun, depending upon the gun’s caliber and choke. The principle is
to put the greatest number of the largest shot the gun will carry into
the rodent body. Thus in 10 and 12 gauge guns shoot No. 8 shot and in
16-gauge guns shoot No. 9 shot, but this varies with each individual
gun. The use of soft lead or chilled shot seems a matter for personal
preference. The charge must be as much as the gun will carry. In the
country smokeless powder becomes a necessity during summer months
since black powder is liable to ignite the dry grass and stubble.

POISONING.

PLASTER FLOUR.

Plaster flour is prepared by mixing one part dry plaster of Paris with
two parts flour or meal. When this is taken in sufficient quantity by
the rodent it produces death by the formation of enteroliths, death
occurring in from four to eight days. This is a poison of uncertain
value and is recommended chiefly on account of its cheapness and small
danger to children and domestic animals. It can not be used in wet
weather, and judging from the small number of rats found dead with
plaster casts in the alimentary canal it is not believed to be very
efficacious.

PHOSPHORUS PASTE.

Phosphorus paste is prepared by mixing crude phosphorus in the
proportion of one-half to 10 per cent in a suitable base. The latter
may consist of cheese, sugar, and oil of anise mixed together and
heated to the consistency of sirup, the phosphorus being added after
the fire has been withdrawn and the mixture begun to cool. Other bases
are cheese, corn meal, and oil of rhodium; cheese, ground fish, or
meat and oil of valerian, glucose, and a small quantity of flour.
Glucose makes an exceptionally good base, as when properly mixed the
poison thus prepared is noninflammable even when heated. The liability
to spontaneous combustion of phosphorus mixtures eliminates their use
in hay, grain, or other warehouses or places where there is danger of
fire or the invalidation of insurance. It should not be forgotten that
phosphorus deteriorates very rapidly, especially when it is exposed to
the sun.

ARSENIC PASTE.

This consists of arsenious acid combined with a base of cheese, meal,
or macerated fish. It may be placed on raisins or prunes and is to be
recommended on account of its stability, the ease with which it is
handled, and the absence of danger from fire. It should, however, be
distributed with great care, every precaution being used to place it
where it is inaccessible to children and domestic animals.

BARIUM CARBONATE.

This has not proven an effective poison owing to the fact that it is
easily decomposed by the vegetable acids, especially lactic and oleic
acid found in cheese and oil. The poisonous effect is not greatly
altered by this change. A disagreeable metallic taste is produced and
the rats will not take it.

STRYCHNINE.

Strychnine is prepared as a poison by soaking wheat over night in
water and subsequently pouring off the excess fluid and placing the
wheat in a caldron containing hot glucose and strychnia sulphate, the
latter in the proportion of one-tenth of 1 per cent. After carefully
stirring so that each grain is thoroughly coated it is dried in
shallow iron pans over a slow fire with constant agitation of the
grain, or by exposure on sheets or canvas to the rays of the sun. This
mixture may be made much more efficient by the addition of cyanide of
potassium in the proportion one-half of 1 per cent. Poisoned grain has
not been found efficient in the destruction of rats, as its bitter
taste causes them to eat little or none of it. It is, however,
particularly efficient in poisoning squirrels, as it is taken readily
by them. The chief objections to its use are its cost, difficulties of
preparation, and liability to its being taken by chickens.

CARBON BISULPHIDE.

Carbon bisulphide is not a poison so much as an asphyxiant. As the
name indicates, it is a two-to-one mixture of sulphur and carbon. The
resulting liquid preparation should be kept in air-tight cans, since
it evaporates quickly. The principle of its efficacy against rodents
is that the fumes are heavier than air and, sinking into a rat or
squirrel hole, drive out the necessary oxygen. To use bisulphide
saturate a small pad of some absorbent cotton, jute, wool, or flannel
material with the liquid, thrust this into the rodents’ burrow, and
carefully stop all apertures through which the fumes might escape.
Animal life of every sort in that burrow is quickly asphyxiated. In
buildings the use of carbon bisulphide is greatly hampered by the
difficulty to confine the gas by stopping all cracks and other
openings. Also the odors of decomposition in animals so killed stand
against its use anywhere but in the country.

Against rats and squirrels in country places carbon bisulphide has
proved one of the best of all weapons. Where it kills, it kills whole
families at a time, not one by one, as must ever be the case with
other poisons and with traps or shotguns. Not only does it kill the
rodent but it also destroys the rodent’s fleas and vermin, which is
most important. A dead infected rat is still a menace, since its fleas
may inoculate other rats and human beings with the infection. Destroy
the fleas and that greatest danger is removed. The recent campaigns
against rodents in the United States have been waged because rats and
squirrels were infected with bubonic plague; hence the added value of
carbon bisulphide. Unfortunately, though this asphyxiant proved so
effective in the work against squirrels in Contra Costa County, Cal.,
it proved to be well-nigh useless during the summer season when dry
heat checks the adobe and makes the ground generally porous.
Nevertheless, the value of carbon bisulphide, especially for sanitary
purposes, can not be easily overestimated for work in the country
during the fall, winter, and spring seasons.

Fumigants in general are effective. They possess no marked or peculiar
advantages as special weapons against rodents. Their use is limited
chiefly to warehouses, elevators, and ship holds. They are deadly to
rats in the same way that they are fatal to every sort of life. Many
difficulties and some dangers stand in the way of their use. It is
safe to advise that no one unacquainted with their action should ever
employ fumigants.

NATURAL ENEMIES.

The war upon rats carried on in San Francisco has proved the great
value of cats and dogs as natural enemies of the rat. That city now
has a law requiring all structures of 800 or less square feet and
outside certain limits to be raised high enough above the ground to
allow access to cats and dogs. (All other buildings in the city must
be rat proof.) An index to the worth of rodent foes in their
extermination points from what happened during the great London
plague. At that time the disease was supposed to be air carried; any
furry material might hold and spread infection. The magistrates
decreed that all cats and dogs should be killed to prevent plague from
lodging and traveling in their hair. Rats were thus free to live and
breed unmolested, and live and breed they did until the plague killed
them off; then and then only did the disease cease its ravages among
human beings.

DOGS.

Slight training will make excellent ratters of Fox, Irish, or Scotch
terriers. Fox terriers have proved especially valuable as retrievers
when shooting squirrels, which in one case out of five will escape to
their burrows unless sharply retrieved.

CATS.

Cats are little less valuable than dogs against rats, while they are
useless against squirrels. The ordinary cat is too well fed to attack
large rats and goes, almost solely, after mice.

All other animals naturally preying upon rodents class with wild
life—weazels, ferrets, badgers, skunks, and minks. These can be used
only in country places, where, however, their raiding of chicken coops
tends to counterbalance their value as ratters. The skunk alone is an
infrequent slayer of fowl, whereas he harvests innumerable farm pests
from worms to crickets. Yet an insurmountable prejudice against skunks
stands in the way of realizing his full usefulness against rodents. In
addition, various hawks and most owls kill off rats. Since rats come
out chiefly in the nighttime, owls have the better chance to be
serviceable in their destruction. The efficiency of these birds in
rural districts quite equals that of a dog against rats, while besides
dogs we have not as yet found a safe natural foe of ground squirrels.

But all such attacks upon rats fail of absolute eradication. One must
make it impossible for them to find sustenance and must destroy not
only all existing rat houses, but also all chance of their digging or
finding new ones.

CUTTING OFF THE RAT’S FOOD SUPPLY.

This is important not alone for its effect in a campaign upon rodents,
but equally because it necessitates sanitary care and cleanliness in
handling foodstuffs intended for humans and garbage coming therefrom.
Abattoirs and places where cattle and hogs are fattened perhaps
furnish the greatest number of rats. Stables, food-supply stores,
groceries, meat, fish and vegetable markets, restaurants, bakeries,
and the various places where food is prepared for human consumption
are usually infested. In each of the places the barriers vary
according to the nature of the premises. Rat-proof receptacles for the
foodstuffs must be installed wherever practical. In San Francisco an
ordinance requires every stable to have metal lined feed bins. Markets
and places where eatables are constantly being shifted about must be
properly screened against rats. Screening should be of heavy wire and
sufficient fineness, not larger than halfinch mesh. In all places the
food has to be raised such a height above floorings as to be beyond
the rat’s reach. This applies also to corn and grain cribs in the
country. Yet, no matter how carefully the bulk of the food may be kept
from rats, negligence in handling it, in spilling or scattering small
amounts upon floors or the ground, will nullify every precaution.

No less painstaking must be the disposition of garbage. Ordinance now
requires that all premises in San Francisco be provided with “sanitary
garbage cans.” Preferably these should be of zinc or galvanized iron
and fitted with tight covers. Under no circumstances should the cover
be allowed to remain off its can. Garbage is to be placed in a can
without delay and care must prevent the dropping of it upon the
ground. Rats once served communities as scavengers; wherever the
scavenger work is laxly done, rats are welcomed. Finally, garbage must
never be allowed to accumulate and should be removed daily, not less
often than every other day.

Special conditions, closely related to the next topic, are encountered
in large warehouses and grain sheds. Places where large quantities of
food may be stored for a length of time should be constructed of
reenforced concrete to be rat proof. Then, again, where vessels are
changing cargoes, rat-proof compounds should be erected for the
temporary storage of freights. The water fronts of seaports are
invariably rat ridden; and in San Francisco a compound for freight
held in transit was found invaluable. No effort can be spared in
keeping rats from their food if their extermination is to be
accomplished.

With regard to ground squirrels, the use of poisoned wheat very
properly enters here. With the changing season ground squirrels change
their habitat and food. During early spring these rodents come down
from their winter dwellings in the hills and seek burrows in meadow
lands and cultivated spots. Months have passed since the squirrel
tasted wheat; his fickle appetite betrays him. From the first spring
months until harvest time one can kill thousands of ground squirrels
by tempting them with poisoned wheat. But so soon as harvest time
comes, they seek new growing green stuffs to eat and thereafter, on
through winter, poisoned wheat is ineffective.

BUILDING THE RAT OUT OF EXISTENCE.

Most certain of all methods to get rid of rodents is to allow them no
place in which to live. San Francisco effects this result through its
ordinance, which requires small houses outside certain city limits to
be raised so high from the ground that dogs and cats can drive out
rats from under them, and which requires all other buildings in the
city to be rat proofed with cement or concrete. The latter
contemplates foundation walls of concrete or brick sunk at least 1
foot to 18 inches to 2 feet above that surface; the whole ground area
inclosed by their foundation walls must be covered with concrete at
least 1½ inches in thickness. Thus the entrance of burrowing rodents
is prevented. Even where buildings stand upon rock or hardpan, these
requirements should be enforced. Rock may crack, gradual weather decay
may cause crevices to be found in it unseen crannies may be found by
rodents, and once the rat lodges in rock his nest is virtually
unassailable. With hardpan it is even worse, for the rats can burrow
in it, with some difficulty, truly, but when nests are impossible
elsewhere, necessity will drive rats to find shelter in hardpan, which
will protect them quite as well as rock. In the main, these two points
of building rats out of existence, though modified, will apply to any
structure.

Yet any negligence will overthrow these safeguards. The principle is
to allow no opening within which rodents may nest. Plank sidewalks and
back yards will continue the rat nuisance even though buildings are
amply protected. Carelessness in throwing old boxes into basements or
piling old lumber or refuse within reach will supply shelter for rats
despite concreted ground area. The precaution must be constant and
consistent.

Another important phase is to cut off the rodent migrations. Prevent
rats from moving from place to place. Their time-honored highway is
through sewers. Modern sewers afford no protection, inviting rodents
to live in them as formerly. Scarcely less important, access should be
stopped. Catch-basin feeding sewers should be constructed so that rats
can not slip through into the mains, or having once gotten in, they
can not escape, and hence must drown. Farms are frequently protected
against rodent migrations by tin or zinc sheeting sunk into the ground
about a foot and a half and standing about the same height above the
surface along the fence line.

Finally, as the progress of rodents from place to place within
communities must be hindered, so must they be stopped from entering
new communities. Railroads and seagoing vessels carry great numbers of
rats in freight. The rat-proof compounds above described serve well
enough so far as railroads are concerned. With vessels it is a
different matter, and one demanding special attention, since the
rodent is only too likely to import infection from foreign harbors.
All hawsers thrown out to make boats fast should be provided with
traps to catch any rat seeking to land along the hawser. San
Francisco, about to possess a rat-proof water front, is now building
concrete wharves to prevent the landing of rodents. Every port should
be safeguarded by stone, concrete, or iron wharves and piers. As a
further protection, all ships should have permanent devices, as is now
proposed for naval construction. Levy’s system of metal conduits built
into vessels promises much in the present world-wide war upon rodents.
Rodents must be “built out of existence,” and to eradicate rats for
all time we must erect wide systems of municipal fortifications.

NATURAL ENEMIES OF THE RAT.

By DAVID E. LANTZ,

_Assistant Biologist, United States Department of Agriculture_.

INTRODUCTION.

Undoubtedly the great increase of rodent pests throughout North
America is in large part due to a general scarcity of the animals that
habitually prey upon them. Since the early settlement of the country
persistent warfare has been made on birds and mammals of prey on the
plea that they are enemies of poultry, game, and insectivorous birds.
Efforts to destroy the predaceous birds and mammals have been greatly
stimulated by the payment of municipal, county, and state bounties,
and the destruction has gone on until in many sections these animals
have nearly disappeared.

The effect of killing off the natural enemies of rodents has been to
disturb natural conditions. Rodents multiply so rapidly that they
derive an undue advantage in the struggle for existence when their
natural enemies are destroyed. The result is noticeable in the
increased depredations of rats, field mice, rabbits, and other pests.

The destruction of carnivorous wild mammals and birds by the farmer,
hunter, or game preserver is often due to misapprehension. Because one
kind of hawk preys on the farmer’s poultry is not sufficient reason
for exterminating all hawks. Nor does the fact that occasionally an
owl or a skunk destroys a chicken or a game bird justify warfare on
all owls and skunks. It is the occasional individual and not the
species that offends.

ANIMALS THAT DESTROY RATS.

The usefulness of the natural enemies of the rat must not be
overlooked in plans for its repression. Among the more important are
the larger hawks and owls, skunks, foxes, coyotes, weasels, minks, and
a few other wild mammals; as well as cats, dogs, and ferrets among
domestic animals, and snakes and alligators among reptiles.

HAWKS.

Most of the larger hawks destroy rats. Feeding only in the daytime,
they seldom find their quarry near houses and barns, where rats do not
venture out until after sunset. Besides, owing to persecution by
farmers, hawks generally keep away from farm buildings. In the open
fields, however, where rats feed in early morning and late afternoon,
hawks find many of the rodents.

The species of hawks that more commonly feed on rats are the buzzard
hawks, including the red-tailed (_Buteo borealis_ and sub-species),
the red-shouldered (_B. lineatus_), the broad-winged (_B.
platypterus_), and the Swainson (_B. swainsoni_); the rough-legged
hawks (_Archibuteo_), two species; and, to a less extent, the marsh
harrier (_Circus hudsonius_), and a few other species.

The writer has several times found the remains of rats about the nest
of the red-tailed hawk. Of the 562 stomachs of this species examined
by Dr. A. K. Fisher, of the Biological Survey, less than 10 per cent
contained poultry or game, while more than 70 per cent contained
injurious rodents.[AH] Most of the other species of buzzard hawks made
a better showing even than this, especially the Swainson hawk, which
had fed entirely on harmful rodents and insects. The stomachs of
rough-legged hawks examined nearly all contained harmful rodents and
none of them contained remains of birds of any sort.

Footnote AH:

Hawks and Owls of the United States, p. 62, 1893.

A few months ago, while walking on the Potomac flats near Washington,
the writer met some boys who had just shot a red-tailed hawk. Its crop
was greatly distended, and later examination showed that the bird had
recently eaten an enormous brown rat. Although the shooting was
contrary to law, when it was reported to the nearest policeman, his
comment was, “Oh, a hawk! Why, it’s a good thing to shoot a hawk.” The
incident illustrates the general popular prejudice against all hawks.

OWLS.

Because they hunt by twilight and at night, owls are more efficient
than hawks in destroying rats. All American owls, except the more
diminutive species, prey on the common rat. Even the little screech
owl (_Otus asio_) feeds on young rats.

Of all our species, the barn owl (_Aluco pratincola_) is preeminent as
a destroyer of rats. It lives commonly about farm buildings, sometimes
even making its nest and rearing its young in the pigeon loft without
molesting the pigeons. In such surroundings its opportunities for
securing rats are excellent, and no other wild bird is so useful on
the farm. The late Henry Newman once stated that every barn owl is
worth £5 a year to the British nation, and the value of the bird to
the American farmer is not less.

Owls, hawks, and other birds of prey that swallow their quarry whole
or in large pieces do not digest the bones, fur, and feathers. They
eject these indigestible parts in the form of large pellets, in which
the fur or feathers surround the bones. The contents of these casts
are an excellent index of the food of owls. Dr. A. K. Fisher, of the
Biological Survey, has examined 987 pellets of a pair of barn owls
that live in a tower of the Smithsonian building in Washington, and in
them found the skulls of no fewer than 192 rats (_Mus norvegicus_),
together with those of 554 common mice and 1,508 field mice (_Microtus
pennsylvanicus_).

Dr. John I. Northrop found a nest of the barn owl on Andros Island,
Bahamas. It contained two young owls and the remains of a black rat
(_Mus rattus_). The ground about the nest was covered with pellets
which contained remains of the black rat and no other species.[AI]

Footnote AI:

The Auk, vol. 8, p. 75, 1891.

The great horned owl (_Bubo virginianus_) is the largest of our
resident owls. It feeds mainly on rodents, though occasionally it
takes a fowl found roosting in an exposed situation, as on a fence or
in a tree. While it occasionally destroys game birds, the rats it
captures would probably destroy ten times as much game as the owl.
Charles Dury, of Ohio, in 1886 published a letter from O. E. Niles in
which it was stated that he counted 113 dead rats at one time under a
nest of this bird.[AJ]

Footnote AJ:

Jour. Cincinnati Soc. Nat. Hist., vol. 8, p. 63, 1886.

The snowy owl (_Nyctea nyctea_) is a rather rare winter visitor in the
northern United States. It usually arrives when the ground is covered
with snow and ordinary food is scarce. Near barns, outbuildings, and
stacks it finds its chief subsistence in the common rat; and, if
undisturbed, will stay for several weeks in the same locality,
destroying many of the pests. Unfortunately, mounted specimens of this
beautiful owl are so much in demand that the majority of them fall a
prey to the specimen hunter and the taxidermist. The destruction of
this bird should be prohibited under heavy penalties.

The barred owl (_Strix varia_), the long-eared owl (_Asio
wilsonianus_), and the short-eared owl (_Asio flammeus_) all destroy
some rats; but as they do not generally nest or live in the vicinity
of farm buildings, the rodents they capture are taken chiefly from the
fields. Occasionally a short-eared or a long-eared owl makes its
winter home in a group of evergreens near the farm buildings, and does
excellent service in clearing the premises of rats and mice.
Evergreens are desirable about a country place, if for no other reason
than that they attract owls.

The practice of indiscriminately destroying hawks and owls should be
discouraged. Game preservers especially should realize that the birds
of prey they kill would, if allowed to live, destroy rats, which in
the course of a year do many times as much harm to game as the
supposed offenders do. Besides, the birds would destroy also large
numbers of mice and injurious insects.

The farmer and the poultry grower may easily learn to recognize the
few harmful species of hawks, and should confine their warfare to
these. The practice of setting pole traps for hawks and owls is
exceedingly reprehensible, as it results chiefly in the destruction of
our beneficial owls when they come about the premises at night in
search of rats. Furthermore, the beneficial hawks and owls should have
legal protection. The larger hawks, nearly all of which are
beneficial, are slow of wing and much more likely to be shot than the
swifter and more harmful falcons.

NATIVE WILD MAMMALS.

Not many species of wild carnivorous mammals live where the common rat
is abundant. Coyotes, foxes, and a few others occasionally find a rat
in the fields, but for the most part they depend for food on native
wild rodents and other animals. Chief among the mammals that do good
work in destroying rats are skunks, minks, and weasels.

SKUNKS.

Skunks are excellent ratters, and when they take up their abode on the
premises of the farmer, they speedily destroy or drive away all rats
and mice. This statement applies equally to the large skunks
(_Mephitis_) and the little spotted skunks (_Spilogale_).
Unfortunately, skunks are seldom allowed to tenant the premises
without being molested by either dogs or men. When undisturbed, they
are inoffensive, and will stay about the farm buildings or stacks
until rats and mice are no longer to be had for food.

Skunks usually hunt by night, and hence poultry properly housed is
safe from them. The larger skunks do not climb, and can capture only
fowls that roost on the ground. Indeed, so few skunks ever learn to
kill poultry that there is no good reason for warfare on the skunk
family. Besides destroying mice and rats, the animals are invaluable
as consumers of noxious insects, especially cutworms, army worms,
white grubs, May beetles, grasshoppers, crickets, and sphinx moths.

WEASELS.

Weasels are good ratters and mousers. Several of our species come
about buildings, and often perform excellent service in destroying
rats and mice. They are more likely than the skunk to attack poultry,
for they can enter the poultry house through smaller openings. At
times weasels seem to kill for the mere love of killing, and while
occasionally this trait makes them formidable in the poultry house, it
also renders them more efficient as destroyers of rodents. A small
weasel can follow a rat into all its retreats, and will soon clear a
stackyard or shed of all rodents.

Our largest weasel, the black-footed ferret (_Putorius nigripes_),
occasionally deserts its wild haunts on the plains and comes about
buildings in search of rats and mice. In 1905, while the writer was at
Hays, Kans., one of these ferrets took up its quarters under a board
sidewalk in the business part of the village. The squealing of the
rats it killed was often heard.

As regards the destruction of poultry by weasels, the same care
necessary to exclude the rat from a poultry house will keep out the
weasel also. When so excluded, a weasel will do no harm about the
premises, but may be depended upon to drive out or kill all the rats
and mice.

MINKS.

Minks are excellent ratters, but as enemies of poultry are worse than
weasels. They destroy fish also. The great demand for mink fur causes
close trapping of these animals, and in the future they are not likely
to influence greatly the numbers of rodent pests.

DOMESTIC ANIMALS.

Among the enemies of rodents often employed as aids to rat destruction
are the dog, cat, and ferret.

DOGS.

The value of dogs as ratters can not be appreciated by those who have
had no experience with trained animals. The ordinary cur and the
larger breeds of dogs seldom make useful ratters. Small Irish, Scotch,
and fox terriers, when well trained, are superior to most other breeds
as ratters, and under favorable circumstances may be depended on to
keep premises free from rodents. Much, too, may be done by the farmer
or householder to increase the effectiveness of his dogs by removing
obstructions to their work. Corncribs and outbuildings, when of wood,
should not have floors close to the ground, but should have ample room
below to permit dogs to move about freely.

With a little preliminary training, most terriers learn to hunt rats
independently, and they thus become doubly useful on farms and in
warehouses.

CATS.

When the black rat was the dominant species in Europe and America,
cats were the chief dependence of the householder against rats; but
comparatively few cats will venture to capture a full-grown brown rat.
Then, too, the ordinary house cat is too well fed and consequently too
lazy to be an efficient ratter.

Occasionally, however, one meets with rat-killing cats whose work in
destroying the brown rat has decided value. These cats are rarely of
the fine breeds, but generally of the common “tabby” variety, kept in
barns or warehouses, fed on milk, and left to forage for their own
meat. Managed in this way, cats are far less objectionable on sanitary
grounds than when kept in the house as pets. In the country, on the
other hand, barn cats are far more likely than the house-kept ones to
run at large and prey upon birds and young poultry. Aside from the rat
itself, we have no more serious enemy of birds and game than half-wild
cats, many of which have been abandoned in fields and woods by the
thoughtless. All things considered, cats do not rank high as
destroyers of the common brown rat.

FERRETS.

Tame ferrets, like weasels, are inveterate foes of rats, and can
follow them into their retreats. Under favorable circumstances ferrets
are useful aids to the rat catcher, but their value is often greatly
overestimated. They require experienced handling and the additional
services of a well-trained dog or two to do effective work. Dogs and
ferrets must be thoroughly accustomed to each other. A noisy or
excitable dog is useless in ferreting. The ferret should be used only
to drive out the rats, which are then killed by the dogs. If an
unmuzzled ferret is sent into rat retreats under floors, it is apt to
lie up after killing a rat and sucking its blood. Sometimes the ferret
will remain for hours in a rat burrow or escape by unguarded exits and
be lost.

Such experiences often discourage the amateur ferreter. Besides,
ferrets are subject to diseases and require the greatest of care as to
their food. For these reasons the use of ferrets to destroy rats,
except in the hands of the experienced, is generally expensive and
disappointing.

OTHER ANIMALS.

MONGOOSE.

The various species of mongoose (_Herpestes_ and _Mongos_) are
destroyers of rats, and their importation into this country has often
been urged. Many years ago they were introduced into Jamaica and
Hawaii to save the sugar plantations from ravages by rats. The
mongoose has, however, proved very destructive to native birds and
poultry in the islands, and its introduction is now generally
regretted. Its importation into the United States is prohibited by
law.

ALLIGATORS.

In the South the alligator is said to destroy many rats along levees
and banks of streams, and its protection has been urged on this
account.

SNAKES.

Our larger snakes are beneficial in destroying rats, mice, prairie
squirrels, and pocket gophers. As most of the food of snakes is
obtained remote from human abodes, only a small percentage consists of
rats.

BOUNTIES ON PREDATORY ANIMALS.

Whatever may be said in favor of bounties on the larger beasts of
prey, those on hawks, owls, and the smaller fur-bearing animals can
not be justified. Payments of this sort should cease, and laws should
be enacted to protect species which careful investigations have shown
to be mainly beneficial.

A few States still pay bounties for the destruction of foxes, weasels,
skunks, minks, and raccoons. All of these, except the southern
weasels, have valuable fur, and hence should be protected as a source
of wealth. In addition they do far more good by destroying rats, mice,
and other field pests than harm to game and poultry.

The payment of bounties on hawks of any kind is open to the objection
that officials hardly ever discriminate between the harmful and the
useful kinds, even when the statutes do so. Since the beneficial kinds
are the more easily captured, public money is often paid out to reward
what really injures the community. The bounty on owls is still more
reprehensible, since owls are a more decided check to rodent increase.

The natural enemies of the rat exercise a steady, cumulative effect in
restricting the numbers of the pest. That the effect is not greater is
largely our own fault, since instead of protecting the birds and
mammals that prey on the rat, we destroy them, sometimes even offering
bounties on their heads. In future our aim should be to increase their
numbers and to protect them in every way possible.

RAT PROOFING AS AN ANTIPLAGUE MEASURE.

By RICHARD H. CREEL,

_Passed Assistant Surgeon, United States Public Health and
Marine-Hospital Service_.

To appreciate the great importance and absolute necessity of rat
proofing as an antiplague measure, it is only necessary to consider
the results that have followed its use as compared with other measures
that have been relied on in recent years in combating this disease.
These were, briefly, disinfection, evacuation, or destruction of
buildings in infected areas, preventive inoculations, and destruction
of rats either by poison or by trapping.

Plague was formerly believed to be communicable by aerial transmission
and through the agency of fomites. Sanitarians have, therefore, put
great faith in disinfection procedures, but the results have never
been satisfactory, and it is only necessary to consider the method of
transmission of plague to perceive the fatuity of bactericidal
measures. Measures intended for the destruction of fleas are also of
relatively small value. It is well worth while to destroy all fleas
possible, but if those infesting the rat population escape, the
efforts will have had little effect in preventing the spread of
plague. It is only those fleas that infest rats and their habitats
that are of importance in relation to the transmission of disease, and
it is only by rat proofing that their destruction in rat burrows and
runs can be accomplished.

Rat-proofing of individual buildings is of no recent date, but new
emphasis was laid on rat-proofing as a separate and distinct
antiplague measure by Passed Assistant Surgeon Mark J. White in an
article written in the fall of 1907.[AK]

Footnote AK:

Journal American Medical Association October 19, 1907.

Disinfecting procedures must be regarded as of minor importance in
plague prevention, except in pneumonic cases where its use is
imperative. It is not intended to depreciate the value of
disinfection, but rather to estimate its exact value as an antipest
measure. Time and money should not be wasted nor a feeling of false
security engendered by using an ineffective measure when others, as
rat proofing, of much greater value are at hand. As an example of this
might be cited an outbreak of plague in one of the refugee camps
during the recent epidemic of the disease in San Francisco. This camp
covered several blocks and housed between two and three thousand
people. The camp grounds throughout and the houses were disinfected
and disinfected well. At the same time, every effort was made to
poison and trap rats. Notwithstanding these precautions, cases
continued to occur, but when the houses were elevated there followed
an immediate cessation of plague cases in the camp.

Another case of infected premises proved equally refractory to
disinfection. The place was a large two-story frame dwelling located
in the center of the city and in a good neighborhood. The yard was
planked, as was also a part of the basement, the latter being used as
a storeroom. On November 1 there occurred in this dwelling a fatal
case of human plague, and plague rats were found at the same time. The
place was disinfected in the usual manner and thorough measures were
taken to trap and poison rats with apparent subsidence of infection,
but on January 22 a plague rat was trapped, followed by another on
January 31, after which the occupant of the building vacated it in
great alarm. All planking was then removed from the yard and basement
and concrete substituted by the owner, the place thereby being
rendered thoroughly rat proof, and no plague rats were subsequently
taken from that dwelling or in its immediate neighborhood.

In 1902 the plague outbreak was almost wholly confined to the Chinese
colony. Chinatown was made the battle ground, and among other measures
rat proofing was enforced, with the result that after the fire it was
by far the most sanitary district in the city of San Francisco from a
structural point of view. The buildings when erected were made rat
proof from cellar to garret. The Chinese had had their lesson, and to
their credit it must be stated that they responded with a greater show
of intelligence than did some of the residents in surrounding
districts.

Adjacent to the Chinese colony is the Latin quarter. In the rebuilding
of this section, no attention was paid to rat proofing; consequently
many of the buildings consisted of small shacks set on the ground or
abutting some insanitary stable, and were therefore ideal rat harbors.
On account of these conditions the natural results followed.
Chinatown, on the other hand, which had contributed in the previous
epidemic almost the entire number of plague cases during the epidemic
of 1907, did not furnish more than two or three of the plague cases
reported; that is, less than 2 per cent of the total cases reported,
while the Italian colony, including North Beach district, probably
furnished over 50 per cent of the total.

The evacuation or burning of buildings can hardly be called a
successful measure any more than a retreat can be styled a victory;
moreover, there can be no question from an economic standpoint as to
the value of rat proofing over abandonment except in a few isolated
cases of dilapidated insanitary property.

Schemes and plans for demurization, total or partial, have been as
numerous and varied as they have been unsuccessful. Traps and poisons
have been the agencies of destruction, but until some highly
communicable epizootic peculiar to rodents shall have been discovered,
absolute eradication of the rat can be considered as nothing less than
impossible.

A recognized authority on plague, Major Morehead, of the Indian
Medical Service, states that “rat destruction is of doubtful value,”
referring, of course, to trapping and poisoning when those measures
are used solely without auxiliary measures. He agrees with Japanese
authorities in their arguments that as rat populations decrease, the
breeding rate among survivors increases, due, obviously, in part at
least, to increased food supply and harboring facilities. Such a
result is assured where rat proofing is not accomplished at the same
time. This latter procedure, by destroying rat harborages and cutting
off food supplies bring about conditions unfavorable to breeding.

The total eradication of rats in a locality is not absolutely
necessary, however, to the eradication of plague. If the rat
population is kept within fairly low limits, rat centers destroyed,
and such rat population as does exist well scattered and not
congested, it is ventured that rat plague will disappear from a
locality. Plague among rats in San Francisco ceased to appear when the
number of rodents was reduced some 50 per cent, but such reduction was
accomplished only after six months of ceaseless endeavor, which
included also the rat proofing of the bakeries, stables, and markets
in the city.

It is a logical supposition that close contact is just as essential
for the propagation of plague among rats as it is for the spread of
certain communicable diseases among human beings, the increase of
cases being in direct proportion to the density of population and
closeness of contact.

RAT PROOFING OF PRIMARY IMPORTANCE.

Without the general enforcement of rat proofing antiplague measures
are bound to be more or less temporary and decidedly unsatisfactory.
This subject is of immense importance to the public, both from a
sanitary and a commercial standpoint, but the latter aspect of the
question is more apt to prove of interest to most communities.

The measures necessary to render buildings rat proof are the same,
however, whether they be instituted for sanitary or for commercial
reasons. Rat proofing will, therefore, be considered entirely from a
sanitary standpoint; but it can be understood that granaries,
bakeries, butcher shops, packing houses, dwellings, and other places,
if rat proofed for sanitary reasons, are just as much protected from
depredation of the rat as though the work had been performed for
commercial reasons alone.

Rat proofing has a twofold objective. It serves as a protection to the
inmates of a building, and excludes rodents from sources of food
supplies and harboring places. While rat proofing should be enforced
as a general measure in all plague-infected localities, it is
imperatively demanded in premises whereon have occurred cases of human
or rodent plague.

Plague-infected localities or places that contain food must be
rendered impervious to rats in order to insure the success of other
preventive measures. Rats can be trapped or poisoned only when other
food supply is excluded. A rat will enter a trap for food or will eat
poisoned preparations not because of their greater attractiveness, but
because of their greater availability. It therefore follows that rat
proofing of food supplies is a prerequisite to success in rat
eradication. The food depots requiring attention in the order of
importance are stables, meat markets, bakeries, restaurants,
groceries, warehouses, and private dwellings.

It is logical to suppose that the most common mode of infection is by
reason of plague rats dying in the walls, roofs, or floorings of human
habitations. As soon as the rat’s body is cold the fleas abandon it
for another rat, some domestic animal, or human being. The risk to
human inmates in such infected houses, therefore, is evident.

That rat proofing is a valuable measure is shown by the reports of the
British Plague Commission where are mentioned the results following
the use of rat-proof “go-downs” and those not so constructed.
Additional evidence is presented by the fact that appalling epidemics
of plague have ravaged India and the China coast, whereas in the
Philippine Islands but few people die of the disease. It would appear
that the comparatively few cases in the Philippine Islands were due to
the fact that most Philippine dwellings are rat proof by reason of
being elevated from the ground and the fact that the walls are thin
and offer no refuge whatever to rats.

RAT PROOFING IS EXPENSIVE.

The almost insuperable obstacle that will usually confront the
sanitary authorities in such work will be either the financial
inability of the unfortunate community or the sordid unwillingness to
make any expenditure that does not promise personal gain.

When the influence of the mosquito in the transmission of yellow fever
was proven, recourse was had to mosquito proofing of both the sick and
the well as a preventive measure. Rat proofing in plague is just as
rational and necessary, but the financial expenditure contemplated
thereby has been of such proportion as to cause the majority of
sanitary authorities in different parts of the world to dismiss the
idea as impossible.

To properly rat proof a city undeniably requires enormous
expenditures, but no antiplague campaign was ever waged without an
immense outlay of both money and labor. If allowed to progress
unchecked, however, plague, either through ravages of the population
or through commercial interference, is ruinous. To fight plague,
therefore, is the only alternative, and a costly campaign should be
anticipated and prepared for in advance. To merely put out traps and
poisons without the preliminary rat proofing required can be
productive of little good and no permanency. Such a plan of campaign
may be attractive because of its relative cheapness, but any city or
country that relies wholly on such measures is practicing false
economy and deferring the day of reckoning.

It becomes evident, therefore, that rat proofing is of the greatest
value as an antiplague measure, and that practical results to be
expected are much greater than with any other method.

As has already been stated, the individual premises on which plague
either among rodents or human beings has occurred demand first and
immediate attention. The work should be extended as rapidly as
possible from the point of infection so as to include the entire block
and neighboring blocks.

While the chief energies should be centered on plague-infected foci,
similar work should be carried on simultaneously throughout the city.

METHODS OF RAT PROOFING.

If plague occurs in the grounds of dwellings the following course
should be pursued: All planked-over areas, including sidewalks, that
might possibly shelter a rat should be removed, leaving either bare
ground or, at the option of the owner, gravel or concrete used, the
gravel being preferable. Small sheds should be elevated, or their
ground floors concreted. Wood sheds should probably be left without
flooring, wood kindling or other contents being piled on elevated
platforms provided for the purpose. Stables on the premises should be
treated as indicated in a subsequent paragraph relating to these
structures.

The garbage depository must be given most careful attention. It should
be a metal receptacle, preferably a galvanized can, water-tight to
prevent seepage which would attract rats, and there should be a
closely fitting lid. A can 2 feet in height without cover will not be
proof against the incursion of rats.

The rat proofing of chicken yards is a difficult task as most chickens
in private families are fed on table scraps, thereby attracting and
supporting a fair quota of rats. The entire inclosure should be
protected by wire fencing 6 feet high and of a mesh not larger than a
half inch. Ordinary poultry netting is inadequate, the mesh being too
large. The edge of the yard should be of concrete construction, the
concrete extending 1 foot upward and 2 feet inward. If, on any
subsequent inspection, rats have been found to have burrowed into the
inclosure, the entire area should be concreted, sand or earth being
allowed as a top dressing.

It would seem sufficient to confine these specifications to a feeding
pen, but in practice this will not suffice, as a mere pretext of such
a place would be built, and the housewife would continue to throw
scraps into the unprotected yard.

The dwelling house itself should receive the most careful attention.
If it is a small frame structure the cheapest and most effective means
of rendering it free from rats is by elevating it, the minimum height
being 1½ feet, measured from the most dependent joist. At the same
time, all underpinning should be freed of rubbish or other material.
It is not sufficient to raise the structure a few inches so as to
permit the entrance of cats and other enemies of the rat. Such height
and exposure must be secured as to deprive all rodents of cover.

If the house is of more substantial structure, and always if it has a
cellar or basement, concrete or some other rat-proof material should
be adopted. If sound foundation walls of stone or brick exist, then
only the addition of a concrete floor is necessary. The stopping up of
rat holes in any substance pervious to rats is at best a poor
expedient.

The grounds must be rendered rat proof by piling all loose materials
at such an elevation as will preclude rat harborage. All rubbish
should be burned or otherwise destroyed. All basement windows should
be properly protected against the ingress of rats, and if the _Mus
rattus_ be present, even second and third story windows should not be
considered too high to afford them entrance.

All loose materials on the premises should be properly piled, even
though they are in a rat-proof cellar. It is not probable that the
_Mus decumanus_ would remain or breed in any place where it could not
burrow; but no encouragement should be offered to any rodent let in by
carelessly left open doors. There have been cases where the black rat
has lived, increased, and overrun a house which was structurally rat
proof, but in which there was allowed easy access through open windows
and doors, and great piles of loose materials and dunnage furnish
harborage.