RAT-CONTROL METHODS

Mifini Biological laboratory

MAR 3-1949

mm% mil mass.

I Circular 13

UNITED STATES DEPARTMENT OF THE INTERIOR

FISH AND WILDLIFE SERVICE

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RAT- CONTROL METHODS

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mm aioiogical Laboratory MAR 3-1949 WOODS HOLE, MASS.

I Circular 13

UNITED STATES DEPARTMENT OF THE INTERIOR

FISH AND WILDLIFE SERVICE

CIRCULAR 13

Fish and Wildlife Service, Albert M. Day, Director United States Department of the Interior, J. A. Krug, Secretary

UNITED STATES GOVERNMENT PRINTING OFFICE

1 948

For sale by the Superiiilendcnt of Documents, U. S. Governnieut rrintiinf Otiice Wiishiiijiton 25, D. C. - Price 5 cents

RAT- CONTROL METHODS

INTRODUCTION

Modern rat-control methods are less a matter of startling new techniques than thorough appli- cation of all principles involved. Merely destroying a few rats here and there does not begin to solve the problem, for man has been killing rats for centuries without halting the spreading of these ob- noxious pests. Fortunately, we are becoming more and more aware of the deadly effect rats have upon our everyday existence. In thus becoming more rat con- scious, we have an ever-increas-

ing possibility of gaining control of one of the greatest spreaders of disease, death, and destruction the world has ever known (fig. 1) . Permanent control is the only satisfactory solution of the rat problem. Sporadic campaigns to destroy rats, although often ef- fective in reducing the numbers for a short period, must be re- peated again and again, with little likelihood of achieving long-last- ing results. Any program, to be successful, must incorporate these four major phases of control : De-

Figure I. — The house rat — spreader of destruction, disease, and death.

struction of rats, elimination of rat harborages, elimination of food supply for rats, and rat- proofing of buildings. Further- more, such a program should re- ceive attention at all times of the year. Once initial success has been attained, maintenance is es- sential, or conditions will soon revert to their former status. A constant watch must be main- tained to repel new invaders as quickly as they appear. Complete and wholehearted cooperation of all concerned, public and private, is the keystone to a successful program.

USE OF POISONS

The most efficient means of ef- fecting wholesale destruction of rats is the use of poisons, or ro- denticides, as they are called. Poisons that are deadly for one warm-blooded animal, however, are also more or less poisonous to others. Human beings, pets, and domestic animals must be pro- tected against accidental poison- ing. Care must be observed in handling the materials and every precaution taken to avoid contam- inating foodstuffs. The poison that best fits the conditions under which it is to be used should be chosen.

POISONS FOR GENERAL USE

For general use those poisons should be selected that can be used by the average person without difficulty, providing instructions are followed and proper precau- tions taken at all times. These include red squill, ANTU, and zinc phosphide.

Red Squill

Red squill is obtained from the bulb of a lily-like plant that grows in the Mediterranean region. It has the peculiar advantage over

other poisons of containing an emetic agent that causes vomiting in most animals other than rats and thereby the poison is elimi- nated. Furthermore, it has a disagreeable taste, so that many animals will not touch it. ISTever- theless, it is a poison and should be treated as such.

Red squill, as imported, lacks uniform toxicity and often may prove to be an unreliable rat poison unless it has been brought up to uniform strength by an extraction process. Purchasers should insist upon obtaining red squill that has a guaranteed mini- mum toxicity not to exceed 500 mg/kg (500 milligrams of the toxic element to a kilogram of body weight of the rat). The most satisfactory results are ob- tained when the poison is mixed with the bait material in the pro- portion of one to nine ; that is, the resulting mixture should contain 10 percent red squill. When dry cereal is used as the base, the red squill should be added to the dry ingredients and the mixture stirred thoroughly before water is added. When meat or fish is used, a thin paste of red squill and water is> prepared, care being taken to avoid lumping, and this is then blended with the bait material.

ANTU

ANTU is the abbreviated name for the chemical alphanaphthyl- thiourea, which is highly toxic to the common brown, or Norway, rat, but much less so to the black and other forms of climbing rats. For this reason ANTU is not rec- ommended for general use in areas in which the climbing rats predominate, as in the Southern States. ANTU is a grayish- white powder, insoluble in water, chemically stable, and nonirritat- ing to the skin of human beings. It kills rats by causing an accu-

mulatioii of body lluids within the chest cavity, literally drowning the animals.

Dogs and other pets, pigs, and day-old chickens are easily killed by ANTU. Although many other domestic animals are more resist- ant to this poison, all precautions should be taken to prevent chil- dren, pets, domestic animals, or foodstuffs from coming in contact with it.

Most effective results are ob- tained when ANTU is used in food baits in a concentration of ly^ percent. It is essential that a complete coverage be made when baiting with this poison. Rats receiving less than a lethal dose build up a tolerance as well as a strong dislike for the material. Operations with ANTU should not be conducted at intervals of less than 4 to 6 weeks. Hence, in a permanent control program in which ANTU is used, it should be alternated with some other ef- fective rodenticide.

Zinc Phosphide

Zinc phosphide is highly toxic to all forms of animal life, and great care must be exercised in its use. It is a dark gray powder, insoluble in water, and has a strong pungent odor character- istic of phosphorous compounds. Although this poison is well ac- cepted by rats, the odor is, to some extent, unattractive to some ani- mals. Zinc phosphide deterio- rates rather rapidly, hence baits treated with it are relatively non- toxic after being exposed several days to the open air. For longer- lasting effects, the baits should be wrapped in waxed paper. As fats and oils increase the absorp- tion of phosphorus in the body, baits composed of these materials give the best results. A small quantity of bacon fat or mineral oil added to the bait mixture will usually prove satisfactory, as well

as make it easier to blond the mix- ture. A 1-percent concentration of zinc phosphide should be used in the baits.

A number of deaths among hu- man beings have occurred from misuse of phosphorous poisons. In view of the hazards involved, the use of other types of phos- phorous compounds and mixtures of the pure element is not encour- aged.

POISONS FOR SPECIAL USE

Poisons consisting of highly toxic substances that are ex- tremely dangerous to all forms of animal life should be used only by trained professional operators.

Sodium Fiuoroacetate or Compound Ten-Eishty

Sodium fiuoroacetate or com- pound ten-eighty is not sold on the open market. Its use is restricted to insured pest-control operators and to qualified Government tech- nicians. There is no antidote for this poison. It is so toxic that merely one-half ounce is mixed in a gallon of water to make a drink- ing bait, and a single sip of this preparation will kill a rat. Fur- thermore, the poison does not dis- integrate upon being swallowed. A cat or a dog that eats dead or dying rats that have received this poison will also be killed. Be- cause of this danger of secondary poisoning, compound ten-eighty should not be exposed indiscrimi- nately out-of-doors or in places where pets or domestic animals are kept. Use of this material, except by trained individuals, is not recommended.

Thallium Sulphate

Thallium sulphate is another deadly substance not recommend- ed for general use. Although not so toxic as compound ten-eighty, it is tasteless and is readily ac-

cepted by rats. It possesses all the hazards of ten-eighty, and in addition it is cumulative and is capable of being absorbed through the skin. Operators handling 'thallium sulphate should always wear gloves. Its use should be restricted to trained technicians.

PREPARATION OF BAITS

Rats are omnivorous; that is, they will eat almost any kind of food available. Like human be- ings, some individual rats have definite preferences which must be catered to, but, generally speak- ing, bait materials consist of ce- reals, meats, fish, cheese, fruits, and vegetables. Any or all of these may be acceptable at any given time. Often a change in the kind of food ofi'ered will produce the greatest success. If the rats have been eating poultry feed, baits with a meat or a fish base may yield the best results. On the other hand, occasionally rats will refuse to touch a food they are not accustomed to eating. More important than the mate- rials used, however, is the proper preparation of the baits. Too much poison in the mixture is just as harmful as too little, for ac- ceptance will be cut down. If the poison is not thoroughly mixed with the bait material, some parts of the bait will have too strong a concentration of the poison, while others will have too weak a one to produce results.

Bait material in small lots, up to a pound or two, can be mixed readily by hand, with a large spoon or paddle, in a mixing bowl, pail, or similar container. Articles used in mixing poisons should be used for that purpose only and kept separate from all other uten- sils. They should be labeled "POISON." Larger lots of bait material are more easily mixed

mechanically. A table-model elec- tric mixer will mix up to about 10 pounds of bait material at a time, a floor model 50 pounds with ease. Mechanical mixing saves labor and results in a more uniform mix than that produced by the hand method. The ingredients should be weighed carefully to insure the proper proportions. No guess work should be allow^ed. Only enough bait for use on the same day as prepared or within a 24- hour period should be mixed at one time. Baits are most accept- able when fresh. A week's supply should not be made up at one time.

PLACEMENT OF BAITS

Of greater importance than the kind of bait used, is the proper placement of the material (fig. 2) . Rats seek shelter and protection in their movements as far as pos- sible. Baits placed in rat travel- ways and harborages are far more likely to be found and sampled than those exposed in the open. Proper placement is necessary also from the standpoint of safety, if children, pets, and domestic ani- mals are to be protected from ex- posure to the poisons. Baits should be placed under cover whenever possible. An old board or a box can be leaned against a barn wall to cover a runway. A permanent bait station for exposing the poi- soned baits can be made from an inverted box with two 2- by 3- inch holes cut in each end. This has the added attraction of pro- viding harborage when trash piles or other rat shelters are cleaned up. In any event, baits should be placed where rats are and where they are moving, and not merely scattered anywhere at the conven- ience of the person exposing them.

Of equal importance is the dis- tribution of enough bait. It is better to put out more than is deemed strictly necessary. The

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Figure 2. — Place poisoned baits where rats regularly travel.

baits should be made into small balls about the size of a walnut or a marble. Care to prevent the odor of the hands from remaining about the baits or the station need not be taken, as rats are familiar with human scent. Sometimes it may be desirable to wrap the baits in a small piece of tissue or waxed paper. This can be done simply by cutting- the paper into 4-inch squares, then folding one square over each bait and twisting the ends. This will keep some baits fresh over a longer period. It also provides a convenient means of handling dry bait mixtures, and affords greater protection to other animals. The main objection to this method is that the rats will often carry the torpedoes, as they are called, back to their nests but will not eat them. When it is desirable that the poisoned baits

should not be carried away, a dry mixture, as corn meal or a feed mixture, may be used and placed in a shallow tray beneath a bait station.

PREBAITING

The most satisfactory results from poisoning operations are ob- tained when areas to be treated are prebaited. This consists of exposing fresh, unpoisoned bait materials prepared exactly as the poisoned baits will be later except for omission of the poison. Pre- baiting will indicate which foods will be most readily accepted, where baits will best be taken, and how much material will be con- sumed at a feeding. Often it will prove satisfactory in stubborn poisoning operations, or in cases where previous poisonings have

been unsuccessful. It is a simple procedure, and the extra time thus spent is well worthwhile.

All sources of food for rats should be removed, particular at- tention being given to such items as garbage cans, stored foods, grain bins, and exposed crates of fruits and vegetables. Trash, piled materials, or other nonfood items should be left where they are until after the baiting has been completed. Runways or bur- rows should not be blocked, as this might arouse the suspicion of the rats or cause them to move.

It is best to use at least three kinds of food baits so selected as to give the rats a choice of moist or dry foods. The following classes, many of the items of which may be obtained from or- dinary kitchen scraps, are sug- gested: Meat: Ground lean beef, beef

melts, liver, sausage, bacon,

chicken entrails, or canned

meat. Fish: Fresh ground raw fish,

canned fish, or cat food. Cereals: Bread crumbs, rolled

oats, corn meal, or chicken

mash. Vegetables: Sliced tomatoes,

green corn, carrots, or lettuce. Fruits: Cantaloups, watermelons,

bananas, or apples. Miscellaneous : Peanut butter,

sweet chocolate, dried milk, or

raw eggs.

Expose the different kinds of bait to be tested in teaspoonful quantities side by side in all spots where rats may be likely to feed upon them. Place baits late in the afternoon or early in the evening, treating the entire area to be cov- ered. Protect the baits from in- terference by cats, dogs, or per- sons. Observe the results the following morning, noting the most acceptable bait, locations wlier^ the bait was taken, and the

quantity of bait consumed. The exact locations of the most fa- vored baits should be noted care- fully, as it is there that the poi- soned baits should be placed later. Remove all uneaten baits. If no baits should be taken readily, skip two nights and then repeat the operations with other baits until an attractive one is found.

When the most acceptable bait has been determined, continue the prebaiting with this material for two or three nights in succession to accustom all rats to baits and locations before adding the poison. Be sure to place the poisoned baits in the same spots as the accepted prebaits.

USE OF POISONOUS GASES

Control of rats by means of poisonous gases includes the fu- migation of buildings and struc- tures, and the gassing of burrows. The fumigation of buildings re- quires considerable preparation and special techniques. It should be attempted only by persons trained for such work, and in many areas the use of poisonous gases is controlled by local regu- lations. In view of the many haz- ards and complications involved, its use in rat control, except by professionals, is not generally recommended.

The gassing of rat burrows out- of-doors is an excellent means of control (fig. 3). Many rats are destroyed under ground, so there is no problem of the disposal of the carcasses. Gas has the advan- tage over poisons of destroying the flea and mite parasites as well, a factor of considerable impor- tance in controlling the spread of some diseases.

The gas most commonly used in rat control is calcium cyanide, in a dust or finely powdered form. It is easily exposed by means of a foot, or stirrup, pump, designed

particularly for the purpose. The nozzle of the hose is inserted in the burrow, the rest of the open- ing sealed with earth, and five or six strokes of the pump handle provide the initial distribution. If gas is seen escaping from other

holes, these, too, should be sealed, or the rats will escape. The valve on the bottom of the pump is then switched over to "air," and the gas is forced through the entire burrow system. Burrows that have been gassed should always

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Figure 3.— Calcium cyanide is forced into rot burrows outside of buildings with a special stirrup pump, OS one means of killing rats.

be broken up with a pick or a shovel the next day and the earth tamped down tightly. The re- maining rats will reopen the bur- rows, and these can thus be de- tected and re-treated until all ac- tivity ceases. This method should not be employed to treat burrows in dirt-floored basements or along- side foundation walls where en- trance to houses is gained.

Calcium cyanide is a deadly poi- son and should be used out-of- doors where it is quickly dissi- pated in the open air. Avoid breathing the fumes. Always pump air through the hose before storing it. The use of calcium cyanide should be curtailed dur- ing freezing or rainy weather.

Carbon monoxide, introduced into rat burrows by means of a hose attached to the exhaust of a gasoline motor, has also been used with a fair degree of success. About 5 minutes running time to a burrow will usually suffice. As carbon monoxide is not so swift acting as calcium cyanide, it re- quires more gas and longer time to take effect.

Carbon dioxide, in the form of dry ice, has been found useful in fumigating refrigerated ware- houses where low temperatures must be maintained to prevent food spoilage. The ice is crushed and distributed through the room. An electric fan will speed up the dispersal of the gas. Carbon di- oxide is used in about a 15-percent concentration, or 30 pounds to 1,000 cubic feet of space, for 24- hour exposure. It has the advan- tage of being much safer to han- dle than are the highly toxic forms of gas.

Other types of poisonous gases are not recommended for general use in rat control.

USE OF TRAPS

In trapping rats the proper placement of the trap is far more important than the selection of a bait. Rats follow natural run- ways whenever possible, running along walls and stacked materials, rather than crossing a room in the open. Their instinct for stealth and desire for protection cause them to pass behind anything that is placed or is leaning against a wall. The best baited trap will rarely entice a rat into the middle of a room, but, on the other hand, a rat will frequently pass over a trap placed along a wall rather than detour wide into the open.

Despite its reputation, cheese is not an infallible bait. Bacon strips, a piece of fresh fish, or bacon-scented oatmeal is better. Such baits should be tied firmly to the trigger of the trap to pre- vent their being taken without springing the trap. Dead rats sliould not be left to decay in the trap. If this should happen, how- ever, the trap should be scalded with boiling water before reusing, but care need not be taken to pre- vent human or rat odors from remaining about the trap. A freshly killed rat in a trap will not frighten other rats away, fre- quently they will even feed upon it. Nor is it necessary to throw a trap away once a rat has been caught in it. If blood or entrails adhere to the trap, they should be scraped off before using it again. The longer a trap is in use, the more likely it is that a rat will approach it.

It is not always necessary to use baited traps. The trigger surface of an ordinary snap trap may be enlarged by using a square of cardboard or a piece of tin, the entire trigger half of the trap be- ing thus made a treadle (fig. 4). A square of corrugated paper.

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\k\ Cardboard trigger
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faco, a thin layer of straw or shredded paper can be used to mask it. By using a hose clamp, with a long bolt projection, a trap can be fitted to a pipe by drilling a hole through the trail and fitting it over the pi-ojecting bolt (fig. 8) . Traps also may be nailed to verti- cal walls where rats climb to holes or runways (figs. 9 and 10).

Figure 4. — Triggers of rat traps should be en- larged with cardboard or hardware cloth.

with the trigger forced between the two layers of paper, will also serve. If desirable, a smear of bait can be rubbed on the surface. Traps with the enlarged trigger surfaces should be placed in such manner as to force the rats to cross over them, as by blocking a runway behind a box or along a beam or a ledge (figs. 5, 6, and 7) . When the trap lies flat on a sur-

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Figure

5. — Traps should

naturally run.

Rat hole Figure 6. — Boxes or boards often may be placed so as to force rats to cross a trap trigger.

11

X

Smcors caused by rots swinging otound roHct

Trop noilcd to side of

im

Dirty smeai couscd by rof .imbing

Trap noiled to studding ocross poth of rot

Figure 7. — Traps should be nailed to walls where rats run or climb.

a

Cr==ZIiri < Tfop no, led to

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Trop let on pipe by means of hose clomp

""^ " Figure 9. — A trap nailed vertically next to a

Figure 8. — A simple device for attaching a runway will often catch rats that avoid traps

trap to a pipe. under foot.

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Figure 10. — Rat traps often may be nailed to the wall where rot runways ore on or near walls. Trigger surfaces should always be enlarged, as shown.

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To insure successful trapping operations, plenty of traps should be used. As with bait, consider- ably more ti'aps should be put out than would seem necessary.

OTHER METHODS

Many other methods and tech- niques for killing rats have been advocated, but the three general methods previously discussed give the most satisfactory results. For the most part, other means of destruction are rarely as efficient, or must be relegated to the role of superstition and folklore. Shooting rats, while sometimes an amusing sport, will not achieve control of an entire population. Small terrier dogs and, rarely, cats will kill occasional rats that they find, but cannot rid the prem- ises of the pests. Ferrets, also, have been used to kill rats, but they are too unreliable and de- stroy too few rats to be a prac- ticable control factor. Such nat- ural enemies as hawks, owls, and snakes should be encouraged to remain about the premises rather than destroyed, but they cannot be relied upon for comiolete con- trol. Repellents of many kinds have been suggested, but, as they dissipate rapidly, their use is lim- ited to small confined spaces, and even there they must be replen- ished constantly. Furthermore, they bring about no decrease in the population. Glue boards, based on the same principle as fly- paper, have been prepared, but they are very messy, and besides, rats soon learn to avoid them.

Virus diseases, supposedly ca- Dable of starting an epidemic among rat populations, have at- tracted some interest, chiefly be- cause of the spectacular nature of the method. Those tried, how- ever, have rarely proved effective.

Rats killed by eating the infected food had to be eaten l^y another rat in order for the disease to he passed on. Furthermore, the bac- teria used belong to the same group as the food-poisoning ba- cilli and have caused some deaths among human beings. Some lo- calities have prohil^ited the sale or use of the so-called rat viruses. For these reasons, they are not recommended.

There are many other methods that are popularly supposed to be eflfective in killing rats, but all have proved ineffective. Ever since the dissemination of the legend of the Pied Piper, man has been searching for some easy way to get rid of rats. The sooner it is realized that downright hard work is the only solution, the sooner adequate control will be attained.

REMOVAL OF RAT HARBORAGES

Unless the places in which rats are living are destroyed and po- tential habitations broken up, con- trol methods are rarely success- ful. Rats can always find enough food available to sustain life. As long as a place to hide and rear young exists, they will continue to survive. Studies have shown that after a poisoning campaign the rat population will regain its for- mer numbers within about 9 months or less if no other control measures are undertaken.

The common brown rat lives underground, beneath stored ma- terials, behind double walls, and in other similar enclosed spaces. After a thorough poisoning pro- gram, these harborages must be eliminated as far as possible. All burrows should be broken up. Stored materials should be placed on racks 12 to 18 inches off the ground (fig. 11). If the woodpile

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Figure

I. — Food and supplies subject to rat damage should be stored on racks high enough to eliminate harborage and permit easy cleaning.

is already stacked for the winter, however, racks for keeping new supphes off the ground should be built. Piles of rubbish and dis- carded material should never be allowed to accumulate. If mate- rials are stored in a dirt-floored shed, they should be kept neatly on shelves or racks, not piled on

the floor. If they are worth keep- ing, they are worth proper storage care. Double walls, made of wall- board or other insulating mate- rial, are favorite harbors for rats. They should be eliminated. If insulation is needed, insulating board can be nailed directly to the wall between the studding. Re-

-Hardware cloth

useful in excluding rats from openings that cannot be closed with brick or mortar.

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moval of these breeding spots not only deprives any remaining rats of a place to live, but renders the place unattractive to any new rats that may stray in.

RATPROOFING

Once the bulk of the rat popula- tion has been destroyed and the harbors eliminated, it becomes necessary to make the buildings as ratproof as possible in order to prevent reinfestation (fig. 12). Cement, hardware cloth of 14-inch or i/^-inch mesh, and sheet metal of 26 gage or heavier are all good ratproofing materials. The exte-

rior of the building should be carefully examined. All openings larger than 1/0 inch must be closed if rats are to be kept out. Wooden sills and doors at ground level should be sheathed in sheet metal to prevent their being gnawed (fig. 13).

Windows less thaji 4 feet off the ground in places where brown rats are present, and at any height from the ground where the climb- ing rats are prevalent, must be screened with hardware cloth. Foundation walls, particularly where utility lines enter the build- ing, should be checked for open- ings and pointed up with cement.

13. — tdgcs of doors or other openings

+h metal

sheaihing.

15

If rats burrow beneath a founda- tion to enter a building, it would be well to install a curtain wall in the shape of an "L" 2 feet deep and 1 foot across the footing. Rats will tunnel down 3 or even 4 feet, but rarely will they cut around the footing. Almost any structure can be made ratproof with a little ingenuity, and usually any measures so taken will at the same time result in useful and worthwhile repairs to the building itself. In the case of open build- ings, as barns and sheds, it is largely a matter of making certain that no harbor is present, so that if a rat does run through the place, it will have no place to hide.

GENERAL SANITATION SUGGESTIONS

Food and shelter are the two most important factors in a rat's existence. It hunts for a food sup- ply and for a convenient harbor- age nearby. Eliminate these two attractants and the premises lose their appeal to rats. Ignore them and new invaders will appear as fast as the old ones are killed off, particularly if nearby areas are also undergoing a control pro- gram. Open garbage and trash heaps should not be permitted. Care should be taken not to spill food on the ground and leave it for rats to get. If birds are being fed,

a rat-proof feeding tray placed on a generous ledge to prevent spill- ing should be provided. In cities, particularly, often more food goes to rats than to the birds. Un- sightly dumps should be eliminat- ed. If complete burning is not pos- sible, the debris should be buried at least 3 feet deep and the earth compacted around it. Every week should be a "clean-up week."

MOUSE CONTROL

In general, the control of mice is based on the same techniques as those used in the control of rats. Trapping, unless the infestation is heavy, will often be sufficient. Of the poisons mentioned, ANTU and red squill give poor results. Zinc phosphide and strychnine alkaloid are more satisfactory. Again, it must be emphasized that care must be observed in the proper handling of the materials, that a sufficient quantity of the mate- rials be used to insure satisfactory results, and that sanitary meas- ures be taken to eliminate condi- tions that permit the pests to exist. Detailed information on the control of mice can be found in United States Department of the Interior Conservation Bulletin 36, Control of Destructive Mice, which can be obtained from the Fish and Wildlife Service, Wash- ington 25, D. C.

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