RAT-CONTROLMETHODS

Mifini Biological laboratory

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RAT-CONTROLMETHODS

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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-CONTROLMETHODS

INTRODUCTION

Modern rat-control methodsare less a matter of startling newtechniques than thorough appli-

cation of all principles involved.

Merely destroying a few rats hereand there does not begin to solve

the problem, for man has beenkilling rats for centuries withouthalting the spreading of these ob-noxious pests. Fortunately, weare becoming more and moreaware of the deadly effect ratshave upon our everyday existence.In thus becoming more rat con-scious, we have an ever-increas-

ing possibility of gaining controlof one of the greatest spreadersof disease, death, and destructionthe world has ever known (fig. 1)

.

Permanent control is the onlysatisfactory solution of the ratproblem. Sporadic campaigns to

destroy rats, although often ef-

fective in reducing the numbersfor a short period, must be re-

peated again and again, with little

likelihood of achieving long-last-

ing results. Any program, to besuccessful, must incorporate thesefour 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. Aconstant watch must be main-tained to repel new invaders as

quickly as they appear. Completeand 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 onewarm-blooded animal, however,are also more or less poisonous to

others. Human beings, pets, anddomestic animals must be pro-

tected against accidental poison-

ing. Care must be observed in

handling the materials and everyprecaution taken to avoid contam-inating foodstuffs. The poisonthat best fits the conditions underwhich it is to be used should bechosen.

POISONS FOR GENERAL USE

For general use those poisonsshould be selected that can be usedby the average person withoutdifficulty, providing instructionsare followed and proper precau-tions taken at all times. Theseinclude red squill, ANTU, andzinc phosphide.

Red Squill

Red squill is obtained from thebulb of a lily-like plant that growsin the Mediterranean region. It

has the peculiar advantage over

other poisons of containing anemetic agent that causes vomitingin most animals other than rats

and thereby the poison is elimi-

nated. Furthermore, it has adisagreeable taste, so that manyanimals 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 mayprove to be an unreliable rat

poison unless it has been broughtup to uniform strength by anextraction process. Purchasersshould insist upon obtaining redsquill that has a guaranteed mini-mum toxicity not to exceed 500mg/kg (500 milligrams of thetoxic element to a kilogram of

body weight of the rat). Themost satisfactory results are ob-

tained when the poison is mixedwith the bait material in the pro-

portion of one to nine ; that is, theresulting mixture should contain10 percent red squill. When drycereal is used as the base, the redsquill should be added to thedry ingredients and the mixturestirred thoroughly before wateris added. When meat or fish is

used, a thin paste of red squill andwater is> prepared, care beingtaken to avoid lumping, and this

is then blended with the bait

material.

ANTU

ANTU is the abbreviated namefor 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 SouthernStates. 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 thechest cavity, literally drowningthe animals.Dogs and other pets, pigs, and

day-old chickens are easily killed

by ANTU. Although many otherdomestic animals are more resist-

ant to this poison, all precautionsshould be taken to prevent chil-

dren, pets, domestic animals, orfoodstuffs from coming in contactwith it.

Most effective results are ob-tained when ANTU is used in foodbaits in a concentration of ly^

percent. It is essential that acomplete coverage be made whenbaiting with this poison. Ratsreceiving less than a lethal dosebuild up a tolerance as well as astrong dislike for the material.Operations with ANTU shouldnot be conducted at intervals ofless than 4 to 6 weeks. Hence, in

a permanent control program in

which ANTU is used, it shouldbe alternated with some other ef-

fective rodenticide.

Zinc Phosphide

Zinc phosphide is highly toxic

to all forms of animal life, andgreat care must be exercised in its

use. It is a dark gray powder,insoluble in water, and has astrong pungent odor character-istic of phosphorous compounds.Although this poison is well ac-cepted by rats, the odor is, to someextent, unattractive to some ani-mals. Zinc phosphide deterio-

rates rather rapidly, hence baits

treated with it are relatively non-toxic after being exposed severaldays to the open air. For longer-lasting effects, the baits should bewrapped in waxed paper. Asfats and oils increase the absorp-tion of phosphorus in the body,baits composed of these materialsgive the best results. A smallquantity of bacon fat or mineraloil added to the bait mixture willusually prove satisfactory, as well

as make it easier to blond the mix-ture. A 1-percent concentrationof zinc phosphide should be usedin the baits.

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

POISONS FOR SPECIAL USE

Poisons consisting of highlytoxic substances that are ex-tremely dangerous to all forms ofanimal life should be used only bytrained professional operators.

Sodium Fiuoroacetate or

Compound Ten-Eishty

Sodium fiuoroacetate or com-pound ten-eighty is not sold on theopen market. Its use is restricted

to insured pest-control operatorsand to qualified Government tech-nicians. There is no antidote forthis poison. It is so toxic thatmerely 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 ordying rats that have received thispoison will also be killed. Be-cause of this danger of secondarypoisoning, compound ten-eightyshould not be exposed indiscrimi-nately out-of-doors or in placeswhere pets or domestic animalsare kept. Use of this material,except by trained individuals, is

not recommended.

Thallium Sulphate

Thallium sulphate is anotherdeadly substance not recommend-ed for general use. Although notso 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 throughthe skin. Operators handling'thallium sulphate should alwayswear gloves. Its use should berestricted 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 havedefinite preferences which mustbe 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 anygiven time. Often a change in thekind of food ofi'ered will producethe greatest success. If the ratshave been eating poultry feed,

baits with a meat or a fish basemay yield the best results. Onthe other hand, occasionally ratswill refuse to touch a food theyare not accustomed to eating.

More important than the mate-rials used, however, is the properpreparation of the baits. Toomuch poison in the mixture is justas harmful as too little, for ac-ceptance will be cut down. If thepoison is not thoroughly mixedwith the bait material, some partsof the bait will have too strong aconcentration of the poison, whileothers will have too weak a one toproduce results.

Bait material in small lots, upto a pound or two, can be mixedreadily by hand, with a largespoon or paddle, in a mixing bowl,pail, or similar container. Articlesused in mixing poisons should beused for that purpose only andkept separate from all other uten-sils. They should be labeled"POISON." Larger lots of baitmaterial are more easily mixed

mechanically. A table-model elec-

tric mixer will mix up to about 10pounds of bait material at a time,

a floor model 50 pounds with ease.

Mechanical mixing saves laborand results in a more uniform mixthan that produced by the handmethod. The ingredients shouldbe weighed carefully to insure theproper proportions. No guesswork should be allow^ed. Onlyenough bait for use on the sameday as prepared or within a 24-

hour period should be mixed atone time. Baits are most accept-able when fresh. A week's supplyshould not be made up at one time.

PLACEMENT OF BAITS

Of greater importance than thekind of bait used, is the properplacement of the material (fig. 2)

.

Rats seek shelter and protectionin their movements as far as pos-sible. Baits placed in rat travel-

ways and harborages are far morelikely to be found and sampledthan 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 shouldbe placed under cover wheneverpossible. An old board or a boxcan be leaned against a barn wall

to cover a runway. A permanentbait station for exposing the poi-

soned baits can be made from aninverted box with two 2- by 3-

inch holes cut in each end. Thishas the added attraction of pro-

viding harborage when trash piles

or other rat shelters are cleanedup. In any event, baits should beplaced where rats are and wherethey are moving, and not merelyscattered 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

PI I lillllll llfMpPWIilpi I

I III I

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

baits should be made into smallballs about the size of a walnut ora marble. Care to prevent theodor of the hands from remainingabout the baits or the station neednot be taken, as rats are familiarwith human scent. Sometimes it

may be desirable to wrap the baits

in a small piece of tissue or waxedpaper. This can be done simplyby cutting- the paper into 4-inchsquares, then folding one squareover each bait and twisting theends. This will keep some baitsfresh over a longer period. It also

provides a convenient means ofhandling dry bait mixtures, andaffords greater protection to otheranimals. The main objection to

this method is that the rats will

often carry the torpedoes, as theyare called, back to their nests butwill not eat them. When it is

desirable that the poisoned baits

should not be carried away, a drymixture, as corn meal or a feedmixture, may be used and placedin a shallow tray beneath a bait

station.

PREBAITING

The most satisfactory results

from poisoning operations are ob-

tained when areas to be treatedare prebaited. This consists ofexposing fresh, unpoisoned bait

materials prepared exactly as thepoisoned baits will be later exceptfor omission of the poison. Pre-baiting will indicate which foodswill be most readily accepted,

where baits will best be taken, andhow much material will be con-sumed at a feeding. Often it will

prove satisfactory in stubbornpoisoning operations, or in caseswhere previous poisonings have

been unsuccessful. It is a simple

procedure, and the extra time thusspent is well worthwhile.

All sources of food for rats

should be removed, particular at-

tention being given to such itemsas garbage cans, stored foods,

grain bins, and exposed crates

of fruits and vegetables. Trash,

piled materials, or other nonfooditems should be left where theyare until after the baiting hasbeen completed. Runways or bur-rows should not be blocked, as this

might arouse the suspicion of therats or cause them to move.

It is best to use at least threekinds of food baits so selected asto give the rats a choice of moistor dry foods. The followingclasses, many of the items ofwhich may be obtained from or-

dinary kitchen scraps, are sug-gested:

Meat: Ground lean beef, beefmelts, liver, sausage, bacon,chicken entrails, or cannedmeat.

Fish: Fresh ground raw fish,

canned fish, or cat food.

Cereals: Bread crumbs, rolled

oats, corn meal, or chickenmash.

Vegetables: Sliced tomatoes,green corn, carrots, or lettuce.

Fruits: Cantaloups, watermelons,bananas, or apples.

Miscellaneous : Peanut butter,sweet chocolate, dried milk, orraw eggs.

Expose the different kinds ofbait to be tested in teaspoonfulquantities side by side in all spotswhere rats may be likely to feedupon them. Place baits late in theafternoon 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 thefollowing morning, noting themost acceptable bait, locationswlier^ the bait was taken, and the

quantity of bait consumed. Theexact 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 nobaits should be taken readily,skip two nights and then repeatthe operations with other baitsuntil an attractive one is found.When the most acceptable bait

has been determined, continue theprebaiting with this material fortwo or three nights in successionto accustom all rats to baits andlocations before adding the poison.

Be sure to place the poisoned baitsin the same spots as the acceptedprebaits.

USE OF POISONOUS GASES

Control of rats by means ofpoisonous gases includes the fu-

migation of buildings and struc-

tures, and the gassing of burrows.The fumigation of buildings re-

quires considerable preparationand special techniques. It shouldbe attempted only by personstrained for such work, and in

many areas the use of poisonousgases is controlled by local regu-lations. In view of the many haz-ards and complications involved,its use in rat control, except byprofessionals, is not generallyrecommended.The gassing of rat burrows out-

of-doors is an excellent means ofcontrol (fig. 3). Many rats aredestroyed under ground, so thereis no problem of the disposal ofthe carcasses. Gas has the advan-tage over poisons of destroyingthe flea and mite parasites as well,

a factor of considerable impor-tance in controlling the spread ofsome 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 afoot, or stirrup, pump, designed

particularly for the purpose. Thenozzle of the hose is inserted inthe burrow, the rest of the open-ing sealed with earth, and five orsix strokes of the pump handleprovide the initial distribution.If gas is seen escaping from other

holes, these, too, should be sealed,or the rats will escape. The valveon the bottom of the pump is thenswitched over to "air," and thegas is forced through the entireburrow system. Burrows thathave been gassed should always

nr ^

Figure 3.—Calcium cyanide is forced into rot burrows outside of buildings with a special stirruppump, 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 burrowsin 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. Avoidbreathing the fumes. Alwayspump 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 agasoline motor, has also been used

with a fair degree of success.

About 5 minutes running time to

a burrow will usually suffice. Ascarbon 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 temperaturesmust be maintained to prevent

food spoilage. The ice is crushedand distributed through the room.An electric fan will speed up thedispersal of the gas. Carbon di-

oxide is used in about a 15-percentconcentration, 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 gasesare not recommended for generaluse in rat control.

USE OF TRAPS

In trapping rats the properplacement of the trap is far moreimportant than the selection of abait. Rats follow natural run-ways whenever possible, runningalong walls and stacked materials,rather than crossing a room in theopen. Their instinct for stealthand desire for protection causethem to pass behind anythingthat is placed or is leaning againsta wall. The best baited trap will

rarely entice a rat into the middleof a room, but, on the other hand,a rat will frequently pass over atrap placed along a wall ratherthan detour wide into the open.

Despite its reputation, cheeseis not an infallible bait. Baconstrips, a piece of fresh fish, orbacon-scented oatmeal is better.

Such baits should be tied firmly

to the trigger of the trap to pre-

vent their being taken withoutspringing the trap. Dead rats

sliould not be left to decay in thetrap. If this should happen, how-ever, the trap should be scaldedwith boiling water before reusing,

but care need not be taken to pre-

vent human or rat odors fromremaining about the trap. Afreshly killed rat in a trap will notfrighten other rats away, fre-

quently they will even feed uponit. Nor is it necessary to throwa trap away once a rat has beencaught in it. If blood or entrails

adhere to the trap, they should bescraped off before using it again.

The longer a trap is in use, themore 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 squareof 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.

10

**i

XSmcors caused by rots

swinging otound roHctTrop noilcd to side of

imDirty 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.

aCr==ZIiri < Tfop no, led to

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.

^^H

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.

12

To insure successful trappingoperations, plenty of traps shouldbe used. As with bait, consider-ably more ti'aps should be put outthan would seem necessary.

OTHER METHODS

Many other methods and tech-

niques for killing rats have beenadvocated, but the three generalmethods previously discussed givethe most satisfactory results. Forthe most part, other means ofdestruction are rarely as efficient,

or must be relegated to the role

of superstition and folklore.

Shooting rats, while sometimes anamusing sport, will not achievecontrol of an entire population.Small terrier dogs and, rarely,

cats will kill occasional rats thatthey find, but cannot rid the prem-ises of the pests. Ferrets, also,

have been used to kill rats, butthey are too unreliable and de-

stroy too few rats to be a prac-ticable control factor. Such nat-ural enemies as hawks, owls, andsnakes should be encouraged to

remain about the premises ratherthan destroyed, but they cannotbe relied upon for comiolete con-trol. Repellents of many kindshave been suggested, but, as theydissipate rapidly, their use is lim-ited to small confined spaces, andeven 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, butthey are very messy, and besides,

rats soon learn to avoid them.Virus diseases, supposedly ca-

Dable of starting an epidemicamong rat populations, have at-

tracted some interest, chiefly be-

cause of the spectacular nature ofthe method. Those tried, how-ever, have rarely proved effective.

Rats killed by eating the infectedfood had to be eaten l^y anotherrat in order for the disease to hepassed on. Furthermore, the bac-teria used belong to the samegroup as the food-poisoning ba-cilli and have caused some deathsamong human beings. Some lo-

calities have prohil^ited the sale oruse of the so-called rat viruses.For these reasons, they are notrecommended.There are many other methods

that are popularly supposed to beeflfective in killing rats, but all

have proved ineffective. Eversince the dissemination of thelegend of the Pied Piper, man hasbeen searching for some easy wayto get rid of rats. The sooner it

is realized that downright hardwork is the only solution, thesooner adequate control will beattained.

REMOVAL OF RATHARBORAGES

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 enoughfood available to sustain life. Aslong as a place to hide and rearyoung exists, they will continue to

survive. Studies have shown thatafter a poisoning campaign therat population will regain its for-

mer numbers within about 9months or less if no other control

measures are undertaken.The common brown rat lives

underground, beneath stored ma-terials, behind double walls, andin other similar enclosed spaces.

After a thorough poisoning pro-

gram, these harborages must beeliminated as far as possible. All

burrows should be broken up.

Stored materials should be placed

on racks 12 to 18 inches off theground (fig. 11). If the woodpile

13

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I

rFigure 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 newsupphes off the ground should bebuilt. Piles of rubbish and dis-

carded material should never beallowed to accumulate. If mate-rials are stored in a dirt-floored

shed, they should be kept neatlyon shelves or racks, not piled on

the floor. If they are worth keep-ing, they are worth proper storagecare. 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 thewall between the studding. Re-

-Hardware cloth useful in excluding rats from openings that cannot be closed with

brick or mortar.

14

moval of these breeding spots notonly deprives any remaining ratsof a place to live, but renders theplace unattractive to any new ratsthat may stray in.

RATPROOFING

Once the bulk of the rat popula-tion has been destroyed and theharbors eliminated, it becomesnecessary to make the buildingsas ratproof as possible in order to

prevent reinfestation (fig. 12).

Cement, hardware cloth of 14-inch

or i/^-inch mesh, and sheet metalof 26 gage or heavier are all goodratproofing materials. The exte-

rior of the building should becarefully examined. All openingslarger than 1/0 inch must be closedif rats are to be kept out. Woodensills and doors at ground level

should be sheathed in sheet metalto prevent their being gnawed(fig. 13).

Windows less thaji 4 feet off theground in places where brown ratsare present, and at any heightfrom the ground where the climb-ing rats are prevalent, must bescreened with hardware cloth.

Foundation walls, particularlywhere 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 wouldbe well to install a curtain wall in

the shape of an "L" 2 feet deepand 1 foot across the footing.Rats will tunnel down 3 or even 4feet, but rarely will they cutaround the footing. Almost anystructure can be made ratproofwith a little ingenuity, and usuallyany measures so taken will at thesame time result in useful andworthwhile repairs to the buildingitself. In the case of open build-

ings, as barns and sheds, it is

largely a matter of making certainthat no harbor is present, so thatif a rat does run through theplace, it will have no place to hide.

GENERAL SANITATIONSUGGESTIONS

Food and shelter are the twomost important factors in a rat's

existence. It hunts for a food sup-ply and for a convenient harbor-age nearby. Eliminate these twoattractants and the premises lose

their appeal to rats. Ignore themand new invaders will appear asfast as the old ones are killed off,

particularly if nearby areas arealso undergoing a control pro-gram. Open garbage and trashheaps should not be permitted.Care should be taken not to spill

food on the ground and leave it forrats to get. If birds are being fed,

a rat-proof feeding tray placed ona generous ledge to prevent spill-

ing should be provided. In cities,

particularly, often more food goesto rats than to the birds. Un-sightly dumps should be eliminat-ed. If complete burning is not pos-sible, the debris should be buriedat least 3 feet deep and the earthcompacted around it. Every weekshould be a "clean-up week."

MOUSE CONTROL

In general, the control of mice is

based on the same techniques asthose used in the control of rats.

Trapping, unless the infestation is

heavy, will often be sufficient. Ofthe poisons mentioned, ANTU andred squill give poor results. Zincphosphide and strychnine alkaloid

are more satisfactory. Again, it

must be emphasized that caremust be observed in the properhandling of the materials, that asufficient quantity of the mate-rials be used to insure satisfactoryresults, and that sanitary meas-ures be taken to eliminate condi-tions that permit the pests to

exist. Detailed information onthe control of mice can be foundin United States Department ofthe Interior Conservation Bulletin

36, Control of Destructive Mice,which can be obtained from theFish and Wildlife Service, Wash-ington 25, D. C.

5 VVHSE 00077

U. S. GOVERNMENT PRINTING OFFICE