Part 15

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oil of anise mixed together and heated to the consistency of sirup, the phosphorus being added after the fire has been withdrawn and the mixture begun to cool.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.