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.