THE RAT AS AN ECONOMIC FACTOR.

By David E. Lantz,

Assistant Biologist, United States Department of Agriculture.

INTRODUCTION.

The world has rightly learned to dread rats as disseminators of disease, and recent efforts to rid cities of the pests have resulted chiefly from sanitary considerations. Yet the material losses due to depredations of rats are now, and always have been, a sufficient argument for their destruction. The requirements of sanitation and public health are slowly bringing to pass what economic interests failed to accomplish, namely, a general recognition of the fact that the rat is a standing menace to prosperity. To point out some of the many ways in which rats inflict injury and the extent to which they drain the resources of the people is the object of the present chapter.

UTILITY OF THE RAT.

Do rats serve any useful purpose? With very slight reservation, the question may be answered in the negative. There have been times and places in which the rat’s work as a scavenger accomplished good, but modern methods of garbage disposal are superseding the feeding it to rats.

It was Robert Southey, the poet, who, nearly a century ago, humorously suggested as the first three steps to eradicate rats—first, introducing them as a table delicacy; second, utilizing the skins; and third, inoculating them with a contagious disease.^[BY] The last of these plans is now receiving considerable attention from bacteriologists, but the others, for obvious reasons, have been neglected.

It is true that under exceptional circumstances the rat has been a source of human food. The principal instances on record were during the siege of Paris in 1870, and during the siege of the French garrison at Malta, 1798–1800, when food was so scarce that rat carcasses brought high prices. Another was on board the ship Advance during an 216arctic winter, when Doctor Kane attributed his entire immunity from scurvy to his diet of fresh rats, of which none of the other members of the party would partake.^[BZ]

The statement is often made in newspapers, and even in encyclopedias, that in Europe, and especially in France, rat skins are extensively used in the manufacture of gloves. The late Frank T. Buckland, about a half century ago, made diligent inquiry in London, and through friends in Paris and other places on the Continent, but found no confirmation of such statement. He concluded that either rat skins were not used for making gloves or the manufacturers were unwilling to acknowledge such a use.^[CA] Personally, the writer has been unable to learn of any demand or market for rat skins at the present time. They are not strong, and the fur is of inferior quality. The occasional finding of one or more rat skins in the fur lining of coats is probably to be explained by the fact that they are sometimes included in lots of small muskrat skins (“kitts”) and overlooked by the buyer.

DESTRUCTIVENESS OF THE RAT.

Rats inflict injury in a surprising number of ways, and before an attempt is made to consider the magnitude of the losses due to these animals a statement of the nature of their depredations should be made.

DAMAGE TO GRAINS.

Cultivated grains are the favorite food of rats. The animals begin their depredations by digging up the newly-sown seed. They eat the tender sprouts when they first appear, and continue destroying the plants until the crop matures. They then attack the grain itself, and after harvest take toll from shock, stack, mow, crib, granary, elevator, mill, and warehouse. When rats are abundant their depredations amount to an appreciable percentage of the entire yield of grain, and in exceptional cases whole crops have been ruined.

INDIAN CORN.

Probably this crop suffers greater injury from rats than any other in the United States. To some extent the animals dig up newly planted corn, but their injury to the maturing grain is far greater. They are especially fond of corn in the milk stage, and often climb the upright stalks and strip the cobs bare. In this way sometimes whole fields are destroyed.

Corn in the shock is often attacked by rats, especially in parts of fields adjacent to hedges, drains, or embankments that afford shelter 217for the animals. A pair of rats often make a corn shock their home, and soon destroy both grain and fodder.

Corn in cribs is often damaged by rats. Many cribs are built close to the ground, and rats take up their abode under the floor. They soon gnaw through the wooden barrier and have free access to the grain. They shell the corn and eat the soft part of the kernels, wasting much more than they eat. They carry the grain into underground burrows and bring up moist soil from below, which in contact with the grain makes it moldy and unfit for market or for feeding to stock. A number of farmers have reported the loss by rat depredations of from a fifth to a half of the contents of a large corn crib during a single winter.

An Iowa farmer, writing to an agricultural journal, relates the following experience:

We had about 2,000 bushels of corn in three cribs to which rats ran, and they ate and destroyed about one-fourth of the corn. Much of it was too dirty to put through the grinder until it had been cleaned an ear at a time. All the time we were poisoning and trapping the rats. We killed as high as 300 rats in two days and could hardly miss them. They destroyed more than enough corn to pay taxes on 400 acres of land.^[CB]

Throughout the United States, but especially in the West and South, corn is often stored for months in rail or other open pens, to which rats have free access. Often the loss in a single season would pay for the construction of rat-proof cribs, or at least for wire netting, that would fully protect the crop.

SMALL GRAINS.

Much has been written about the rat as a house and barn pest, but its depredations in the fields have usually been overlooked. In some localities the common rat, as well as the house mouse, swarms in the fields, especially in summer, and subsists entirely upon the farmers’ crops.

Stacked grain is peculiarly exposed to rat depredations. In the United States, although the cost of protection is small, rats are seldom fenced away from stacks, and, if threshing is delayed, serious loss results. Often, at the removal of a stack, large numbers of rats are discovered, which have been living at the expense of the farmer. As early as 1832 a farmer in Frederick County, Md., with the help of men and dogs, killed 217 large brown rats from one stack of rye.^[CC] In England instances are on record of the killing of over a thousand rats from one stack of wheat.

The destruction of feed by rats is a serious loss not only on the farm but also in city and village. The feed bin or barrel is often left uncovered and rats swarm to the banquet thus exposed. Small 218feeders suffer greater proportional losses, for managers of larger barns recognize the enormous drain and usually provide rat-proof bins, if not rat-proof stables. When rats have access to a stable they take a good share of the feed directly from the mangers, but the loss is seldom noticed.

Rats are exceedingly fond of malt, and in malt houses and breweries constant watchfulness is needed to prevent losses. Mills, elevators, and warehouses in which grain and feed stuffs are stored are subject to constant invasion by rats and mice.

A full-grown rat consumes about 2 ounces of grain daily. A half-grown rat eats nearly as much as an adult. Fed on grain, therefore, a rat eats from 45 to 50 pounds a year. The cost depends somewhat on the kind of grain. If wheat, the value is 60 to 75 cents; if oatmeal, about $1.80 to $2. Several feeders of horses in Washington, D. C., estimated the cost of keeping each rat on their premises at $1 a year. Even though half the grain eaten is waste, the direct loss from this source to feeders is enormous.

MERCHANDISE IN STORES AND WAREHOUSES.

The loss from depredations of rats on miscellaneous merchandise in stores, markets, and warehouses, is second only to the losses on grains. Not only are food materials of every kind subject to attack, but the destruction of dry goods, clothing, books, leather goods, and so on is equally serious. Merchandise other than foodstuffs is usually destroyed for making nests, but books and pamphlets, especially the newly bound, and some other articles, furnish food in the glue, paste, oils, or paraffin used in their manufacture. Some kinds of leather have a peculiar attraction for rats, while others are never touched. Shoes are seldom gnawed unless they have cloth uppers or are made of kid. New harnesses are not often attacked, except collars, which contain straw, and cruppers, which are stuffed with flaxseed. Old harness leather is salty from the perspiration of horses, and rats and mice gnaw it for this reason. Kid gloves and other articles made of similar leather are often destroyed by rats.

Lace curtains, silk handkerchiefs, linens, carpets, mattings, and other dry goods in stores are often attacked by rats. Some of the stuffs contain starch, which serves as food, but most of them furnish nesting materials only. A slight injury makes these articles unsalable; this is especially true of white goods, which are easily ruined by soiling. Nearly all large dry goods and department stores suffer heavy losses from rats. Grocers, druggists, confectioners, and other merchants also have similar experiences, and to the direct losses must be added the sums expended in fighting the pests.

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MERCHANDISE IN TRANSIT.

Merchandise billed for shipment often lies for days in stations and warehouses or on wharves, where depredations of rats and mice cause heavy losses to shippers and consignees. Similar losses occur on boats carrying merchandise from port to port.

Fruits and vegetables in transit on steamboats are often destroyed or damaged by rats. Tomatoes, cucumbers, sweet potatoes, bananas, oranges, grape fruit, peanuts, and similar produce shipped by water from the South, especially in winter, reach northern markets with a large percentage of loss.

In view of the practicability of destroying rats on ships by fumigation, and the ease with which rat-proof compartments for stowing produce can be constructed, it would seem that losses of this nature should be entirely prevented.

POULTRY AND EGGS.

Aside from disease, the greatest enemy of poultry is the rat. The loss from rats varies with their abundance and the care taken to exclude them from the poultry yard. The magnitude of the damage is not generally known, because much of it is blamed on other animals, particularly minks, skunks, and weasels. Much of the injury occurs at night, and the actual culprit is seldom detected. Farmers have heard that minks, skunks, and weasels prey upon poultry. What more natural than to conclude that one of these animals is doing the mischief, especially if one has been seen about the premises?

Rats often prey upon small chicks, capturing them in the nests at night or even about the coops in the daytime. The writer has known rats to take nearly all the chicks on a large poultry ranch, and over a large section of country to destroy nearly half of a season’s hatching. Young ducks, turkeys, and pigeons are equally liable to attack, and when rats are numerous, are safe only in rat-proof yards.

A writer in a western agricultural journal states that in 1904 rats robbed him of an entire summer’s hatching of three or four hundred chicks.^[CD] A correspondent of another newspaper says, “Rats destroyed enough grain and poultry on this place in one season to pay our taxes for three years.”^[CE] When it is remembered that the poultry and eggs marketed each year in the United States have a farm value of over $600,000,000, it will be seen that a small percentage of loss represents an enormous sum.

The destruction of eggs by rats is great, not only on the farms where they are produced, but also in the markets. Commission men and grocers complain of depredations upon packed eggs. The 220animals break and eat a few eggs at the top of a case and the broken yolks run down and soil the eggs below. Then, too, rats carry away unbroken eggs, displaying much ingenuity in getting them over obstacles, as up or down a stairway.

A commission merchant in Washington, D. C., states that he once stored 100 dozen eggs in a wooden tub in his warehouse and left them for nearly two weeks. He then found that rats had gnawed a hole through the tub, just under the cover, and had carried away 71½ dozen, leaving neither pieces of shell nor stains to show that any had been broken.

Besides their destruction of eggs and young fowls, rats eat much of the food put out for poultry. They are destructive also to tame pigeons and their eggs, but particularly to young squabs. They climb the wire netting and gain entrance to the cages through the same openings by which the pigeons come and go. Fanciers are often put to great trouble to protect their pigeons from rats, and because of these pests some of them have abandoned the business.

GAME AND WILD BIRDS.

The rat is the most serious pest in European game preserves. A writer in Chambers’s Journal says:

In a closely preserved country at the end of an average year the game suffers more from the outlying rats of the lordship than from the foxes and mustelines together. The solitary rats, whether males or females, are the curse of a game country. They are most difficult to detect, for in a majority of cases their special work is supposed to be done by hedgehog, weasels, or stoat.^[CF]

The propagation of game birds is becoming a promising industry in the United States. The difficulties of the business are not yet fully known, but the rat is an enemy with which the raiser of game will have to contend. The animal has already proved itself a foe in American pheasantries.

Our wild native game birds are less subject to rat depredations than birds kept in confinement. The nests of ruffed grouse are in woodlands; those of the prairie hen and related species are on plains remote from the haunts of rats. The quail, however, often makes its nest within the summer range of rats, which destroy many of its eggs.

Rats are said often to destroy the nests of wild ducks, woodcock, and other marsh birds. Terns have been entirely driven from their nesting grounds in this way. In England the common tern was extirpated from the Thames marshes; and on Loggerhead Key, Tortugas Islands, off the Florida coast, rats recently nearly exterminated a colony of least terns by destroying the eggs.

221The nests of many ground-nesting and other song birds are robbed by rats. Crows, jays, snakes, and skunks are blamed for most of the destruction and the actual offender seldom suspected. While the other animals named do part of the mischief, the rat is a more serious foe of song and game birds than any of these.

FRUITS AND VEGETABLES.

A well-known form of damage by rats is the destruction of fruits and vegetables in cellars and pits. Apparently no garden vegetable or common fruit is exempt from attack. But the rat does not confine its depredations to stored fruits and vegetables. It attacks ripe tomatoes, melons, cantaloupes, squashes, pumpkins, sweet corn, and many other vegetables in the field; and often the depredations are attributed to rabbits or other animals, which may or may not be concerned in the mischief.

Rats are fond of the small fruits, eating not only the fallen but climbing vines and canes to obtain the ripe grapes or berries. They eat also apples, pears, cherries, and other fruits. The brown rat, while not so expert as the black or the roof rat, readily climbs trees and obtains fruit even at the extremities of the branches.

Among tropical fruits injured by rats are oranges, bananas, figs, dates, cocoanuts, and especially the pods of cacao (Theobroma cacao), from which chocolate is manufactured. H. N. Riddey, writing of his experiences on the island of Fernando do Noronha, South America, mentions the destructiveness of rats in this penal colony. They climb the cocoanut palms and papaw trees to devour the fruit, and do mischief in melon patches. To lessen the evil, each convict was required to bring in a certain number of dead rats, and battues were held monthly to satisfy the requirement. Sometimes the number killed in a single hunt reached 20,000.^[CG]

Fruits and vegetables grown under glass are subject to injury by rats. The animals usually find entrance to greenhouses by way of openings for pipes or drains.

FLOWERS AND BULBS.

Rats attack seeds, bulbs, and the leaves, stems, and flowers of growing plants, whether in the greenhouse, propagating pits, or elsewhere. Of flowering bulbs, the tulip suffers most from rats. Hyacinths also are eaten; but, probably because they are slightly poisonous, narcissus and daffodil bulbs escape injury. Rats eat pinks, carnations, and roses, cutting the stems off clean. They denude geraniums of both flowers and leaves. They attack the choicest blooms of chrysanthemums and carnations in markets, stores, and exhibition rooms, causing heavy losses.

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FIRES.

Rats and mice cause many fires. Several specific instances have been reported by the fire department of the city of Washington within the past two or three years. It is likely that some of these fires are caused by rats gnawing matches. The animals are fond of paraffin, which is often used to protect match heads. They carry the matches to their nests, which are composed of paper and other combustible materials, and the conditions for a conflagration are ready. Since the heads of matches contain from 14 to 17 per cent of phosphorus, actual gnawing is not required to ignite them, but heat or friction from any cause may suffice.

Fires in mills or warehouses have sometimes been traced to the spontaneous ignition of oily or fatty rags and waste carried under floors by rats. Cotton and woolen mills are said to be peculiarly subject to fires of this kind.

Sometimes rats cause fires by gnawing through the lead pipes leading to the gas meter. Workmen or others, searching for the leak, accidentally ignite the gas. Phillips’s warehouse, London, was twice badly damaged by fires originating in this way, and in several instances the sleeping inmates of houses have been in danger of asphyxiation by gas freed in this manner.

The most common way in which rats and mice cause fires is by the destruction of the covering of electric light wires under floors or in partition walls. A considerable percentage of the enormous fire losses in the United States is caused by defective insulation of wires. After wires are once in position rats are the chief agents in impairing the insulation. These animals do much mischief also by gnawing off the coverings of telephone wires. In the case of electric light wires the covering is probably used by the rats for nesting material, but frequently the paraffin in the insulation is the object of attack.

BUILDINGS AND FURNITURE.

Rats seem to be able to gnaw through almost any common material except stone, hard brick, cement, glass, and iron; neither wood nor mortar suffice to keep them out of bins or rooms. They sometimes gnaw through walls or doors in a single night. In the same way they enter chests, wardrobes, bookcases, closets, barrels, and boxes. Almost every old dwelling bears evidence of its present or former occupancy by rats. Often the depreciation of houses and furniture is largely due to marks left upon them by rats—marks that paint and varnish can not hide.

Damage to dwellings by rats is a large item. The decay of sills and floors is hastened by contact with moist soil brought up from rat burrows. Ceilings, wall decorations, and floor coverings are flooded 223by leaks in lead pipes or wooden tanks gnawed by rats. Bricked areas and even foundations are undermined and ruined by rats. All this is real waste and a constant drain on the resources of the country.

MISCELLANEOUS.

A few instances of miscellaneous damage by rats may be mentioned to show the great variety of mischief chargeable to the animals.

A Washington, D. C., merchant reported that at one time rats in his store destroyed 50 dozen brooms worth $2.50 a dozen. In another store, in a single night, they broke $500 worth of fine chinaware on shelves and tables. A dealer in harness reported the loss of $400 worth of collars in one season. The manager of a restaurant complained of an average loss of $30 a month in table linen ruined by rats and mice. A hotel reported the destruction of $75 worth of linen in a month.

At Mobile, Ala., in March, 1908, lost jewelry worth $400 was recovered from a rat’s nest in the home of Señor Viada.

In London rats at one time killed all but 11 out of an aviary of 366 birds.

At Hamburg, Germany, Carl Hagenbeck once had to kill three young African elephants because rats had gnawed their feet, inflicting incurable wounds.

Rats often gnaw the hoofs of horses until they bleed. They kill young lambs and pigs, and have been known to gnaw holes in the bodies of very fat swine, causing death.

Like the muskrat, the brown rat often burrows into embankments and dams, causing serious breaks.

The rat is one of the greatest enemies with which the sugar planter has to contend, destroying acres of growing cane.

In rice plantations rats not only break down and destroy the growing crops, but burrow into the dikes and flood the fields at the wrong season.

On the London docks and on shipboard ivory is often badly damaged by rats. They select for attack the greenest tusks, which are the more valuable.

Mail sacks and other kinds of bagging are greatly injured by rats. The consequent loss and necessary outlay for repairs are a large item in post-office expenditures and in mills and other places where bagging is used.

About the year 1616 rats caused a two years’ famine in the Bermudas. In the southern Deccan and Mahratta districts of India rats ate a large part of the scant crops of 1878 and 1879, and were regarded as in a great measure responsible for the severe famine which followed.^[CH] A writer in Chambers’s Journal stated that the Dutch 224abandoned the Isle of France (Mauritius) in 1610 because of the great abundance of rats.^[CI]

AMOUNT OF LOSSES CAUSED BY RATS.

The damage done by a single rat varies greatly with the circumstances. We have already stated that the cost of feeding a rat on grain varies from 60 cents to $2 a year. Assuming that much of the rat’s food is waste, each rat on a farm will cause a loss of over 50 cents a year. In cities the damage by a single rat probably averages more than in the country. Hotel managers and restaurant keepers state that $5 a year is a low estimate of the loss inflicted by a rat. In making an estimate it should be remembered that the rat is to be charged not only with the food it actually consumes but also with what it destroys or pollutes and renders unfit for use.

If an accurate census of the rats in the United States were possible, and if the minimum average loss caused by a rat were known, an estimate of the total annual losses from their depredations could be made. It was on such a minimum basis that the Incorporated Society for the Destruction of Vermin arrived at their total estimate of £15,000,000 ($73,000,000) as the yearly losses from rats in Great Britain and Ireland. Three propositions were assumed: first, that in cities and villages the number of rats equals the population; second, that in the country there is at least one rat for every acre of cultivated land; third, that each rat in the kingdom inflicts a damage of at least a farthing per day. Circulars asking whether these assumptions are excessive were distributed throughout the country. From 90 to 99 per cent of the replies fully indorsed each of the assumptions.

It can readily be seen that the English basis of estimate would not apply to farm conditions in the United States, where the area in the twelve leading crops alone is over 250,000,000 acres. On a basis of a rat per acre and damage of a farthing per day the annual loss on this area would be $450,000,000, a sum much too great for serious consideration. However, in the more thickly populated parts of the country an estimate of one rat per acre would not be excessive; and it is probable that in most of our cities there are quite as many rats as people. Yet it would be unsafe, owing to our vast territory and varying conditions, to make these assumptions the basis for conclusions.

Over a year ago the writer made an attempt to investigate actual conditions, and thus arrive at an estimate of the total damage by rats in the cities of Washington and Baltimore. From the data obtained the direct annual damage in the two cities was calculated at $400,000 and $700,000, respectively. The Census Bureau in 1906 estimated 225the population of these cities at 308,000 and 554,000, respectively. If the estimates of damage were correct, the average loss for each person is $1.27 a year; and, on the same basis, the 28,000,000 of urban population in the United States (census of 1900) sustains an annual direct injury of $35,000,000 from rats. This is considerably lower than on the English assumption, which would make the losses in our cities over $50,000,000.

Denmark (population 2,500,000) has an estimated rat bill of about $3,000,000 a year, or $1.20 a person. Germany (population 56,000,000) is said to sustain a loss from rats of 200,000,000 marks ($47,640,000) a year, or about 85 cents for each person. The per capita estimate for the United Kingdom is about double that made for Germany. In France the loss from rats and mice for a single year (1904) was placed at $38,500,000, or a little over a dollar for each of its 38,000,000 inhabitants. These estimates are supposed to include only direct losses, but they vary enough to show that no common basis can be assumed for all countries. With present information, therefore, any attempt to state the amount of loss from rats in the United States would be largely guesswork. Considering the population and wealth of the country, however, and the vast area over which rats are abundant, it is not unreasonable to conclude that in the United States the losses from rats amount to much more than in any of the other countries named.

INDIRECT LOSSES.

To the direct losses caused by rats must be added the cost of fighting the animals and of protecting property from them. In our larger cities a number of so-called expert rat catchers are to be found, who operate with dogs, ferrets, traps, poisons, or other means, and who have an extensive clientage among merchants, hotel managers, and others. These pay the rat catcher a yearly or monthly stipend to keep their premises free of rats and mice. Some of the large establishments pay $200 to $600 yearly for such service. While the agreements are seldom kept in full, the clients are usually satisfied that results warrant the expense. Even when no contractor is employed, merchants are at expense for traps, poisons, the keep of cats or dogs, and other means of fighting rats. The same is true in less degree of nearly every householder.

The cost of protecting property from rats is no small item. It increases the expense of nearly all building, but it greatly reduces direct losses from the animals. The economy of rat-proof construction is everywhere manifest, in city or country, and the necessity for it can not be too strongly emphasized.

226Depreciation of property and loss of rents and custom are items not generally thought of in connection with rat damage. A few years ago the writer knew of almost an entire block of city houses that remained untenanted for several months, because infested by rats. As the houses were otherwise desirable, the loss of rent to the owners was probably nearly $2,000. The presence of rats in markets, hotels, and restaurants inevitably results in loss of custom, besides the direct damage by the rodents.

From every point of view the keeping of rats is exceedingly expensive, and the sooner our population can be made to realize the enormous drain upon our resources caused by these rodents the sooner can concerted measures for their destruction be made effective.

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