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PRESEN-T ED

BY

The Trustees

OF

THE BRITISH MUSEUM.

BRITISH MUSEUM (NATURAL HISTORY)
Economic SERIES No. 8

RATS AND MICE

AS

HNEMIES OF MANKIND

BY

M. A. C. HINTON

WITH 2 PLATES AND 6 TEXT-FIGURES

LONDON

PRINTED BY ORDER OF THE TRUSTEES OF THE
BRITISH MUSEUM

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PREFACE

——4-

THE issue of a pamphlet dealing with Rats and Mice, and their
depredations, needs no defence, and it may indeed be claimed to
have a very direct bearing on the successful conduct of the war.
Although the extent of the damage done to essential food-supplies
by these small mammals is appreciated by all those who have had
practical experience on a large scale, it is not sufficiently recognized
by the majority of the community how great it is. The account
given by Mr. M. A. C. Hinton in these pages shows how urgent is
the necessity for co-ordinated action in reducing the numbers of
Rats and Mice, which may fitly be described as the Enemies of
Mankind, by reason of the enormous toll they take of his food, and
of their agency in the dispersal of some of the most serious diseases
which affect the human race.

Plates 1 and 2 and Text-figure 1 have been reproduced from
original drawings by Mr. P. Highley, and fig. 2 from drawings by
the author, Mr. Hinton. Figs. 3-6 are taken from Mr.G.§. Miller’s
“Catalogue of the Mammals of Western Europe,” published by
the Trustees in 1912.

The thanks of the Trustees are due to the following persons
for information or the loan of papers :—

Dr. E. P. Mansy and Dr. Hammonp Smitx of the Local
Government Board. |

The Secretary, the Librarian, and Mr. F. A. Fuurorp, of the
Board of Agriculture and Fisheries.

Dr. W. H. Hamer, Medical Officer of Health for the County of
London, and Dr. BrinckeEr, of the Public Health Dept., L.C.C.

Dr. Wi~LoucHBy, Medical Officer of Health to the Port of
London.

The Port of London Authority and its officers.

The Right Hon. J. W. Lowtusr, D.C.L., LL.D., Speaker of the
House of Commons.

Dr. A. E. Suretey, F.R.S8., Master of Christ’s College, Cam-
bridge.

Mr. R. I. Pocock, F.B.S.

Mr. R. E. Parker, of Easton, Norwich.

Mr. A. H. Parterson, of Yarmouth.

SIDNEY F. HARMER,
British Museum (Naturau History), Keeper of Zoology.
CROMWELL Roap, Lonpon, S.W. 7.
July, 1918.

CONTENTS

oe ee Ee
PAGE
PREFACE ; ; : ; : ; ; ; : ill
CONTENTS . : / ; . ; ; ; Vv
List oF ILLUSTRATIONS. ; P $ sae WL
INTRODUCTION ‘ : : ; ‘ : ; : IX
1. Rats.
FEATURES DISTINGUISHING THE Brnack Rat FROM
THE Brown Rat 3 ; 1
Buiack Rat, SUB-SPECIES AND Histone ; 2
Brown Rat, Races anp History . 3 ' : 5
Rats, GENERAL Hapits . : - ; : 6
BrEEpDiING Hapits ; ; : , 10
Economic IMPORTANCE . f ? 13
In RELATION TO DISEASE . F ; : 16
PLAGUE . ; ; ‘ ; : , v7
TRICHINOSIS : : 18
INFLUENZA AND Oven eres oF DoMESTIC
ANIMALS : : ; f > 0
CONTAMINATION OF Foop . : ; 21
THE PossIBILITY OF THE EXTERMINATION OF Rats 21
Rat PREVENTION AND Rat EXTERMINATION ; 28
2. Housr Mice.
DISTINGUISHING FEATURES OF Common MOUSE . Pak ¥
History ; : ; : : : ¢ ; 38
GENERAL Hapsits . , s - 39
BREEDING Hapits . ; : ; ' ; ; 39
Economic IMPORTANCE . ; : : ; 40
RELATION TO Pusuic HEALTH ; ; ; ; 40
Movusk PiLaGues : : : ; ; 40
ConTROL OF THE MOUSE Pornnen ; : . 492,
3. THE BanANcE or NATURE AND THE PROTECTION OF
CARNIVORA ; ; ; 2 ‘ ee:
4. NoTEs oN STRUCTURE AND CLASSIFICATION OF THE
MvRIDAE, WITH A Kry To BritisH SPECIES . 48
5. TABLE SHowinGc AssuMED Rate or INCREASE IN Rat
POPULATION . . : : : : : ; 60

6. LitERATURE ‘ : ‘ ; i : , > 62

ee ial a Et

LIST OF ILLUSTRATIONS

PLATES.

Brack Rat (Rattus rattus) :
To face page 2
Brown Rat (Rattus norvegicus) :

TEXT-FIGURES.

PAGE
House Mouse (Mus musculus) ; : ‘ GREE
Fie~p Voue (Microtus agrestis), SKULL. 4 ois Ae
Upper Inctsors oF Rattus AND Mus. j f ae a
CHEEK-TEETH OF Cricetinae AND Muicrotinae : ci 2a@
CHEEK-TEETH OF Murinae ; : ‘ ‘ ices cere

Sxuuxts oF Muridae : i 3 i ; 58, 59

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INTRODUCTION

Rats and mice, with some of their near relations, constitute a
great zoological family, the Mwridae,* which belongs to the order
Rodentia. This order comprises the mammals characterised by a
propensity for gnawing, a function performed by a pair of ever-
growing chisel-like teeth, or incisors, placed in the forepart of each
jaw. The distinction between a rat and a mouse is mainly one of
size; larger species, such as those with a hind-foot measuring
more than 30 mm.t in length, are “rats’’; smaller species, with
hind-feet less than 30 mm. long, are ‘“ mice.”

Besides some native wild Mwuridae, Great Britain possesses
three species which have been introduced, at different dates, from
abroad; these aliens are the Black Rat (Rattus rattus), the
Common Rat (R. norvegicus), and the House Mouse (Mus
musculus). Possibly these three species are the most highly
organised members of their family; but unquestionably they are
the most successful of mammals. They are clearly of Asiatic
origin; but uninvited, and unfortunately for us, they have linked
their fortunes with those of humanity. Human enterprise, in all
its phases, and human negligence have disturbed the balance of
Nature in favour of these species, have afforded them an unnatural
degree of protection from their many enemies, a large and

* In a strict zoological sense the names “ rat’? and “‘ mouse”’ are only
applied to members of the Muwrinae—one of the many sub-families into which
the Muridae are divided. The three species which are the subjects of this
work belong, of course, to the Murinae.

For the convenience of those who may wish to acquire a slightly more
extensive knowledge of the Mwridae, and would like to be able to distinguish
the species inhabiting Britain, the writer has prepared a short account of the
structure, classification, history and distribution of the principal divisions of
the family. This, together with a “key” to the characters of the British
forms, appears as an appendix (pp. 48).

t 25 millimetres = 1 inch.

x Introduction.

unmerited share of the world’s foodstuffs, together with perfect
travelling facilities. Small wonder then that these creatures have
invaded and colonised all lands, including those, like North and
South America, which possess no native true rats or mice; that
they have developed into serious pests, taking a heavy toll from
human prosperity, and forming a most deadly menace to the
public health.

The objects of this pamphlet are to give a brief account of
these noxious animals, their habits and breeding; to deal with
their economic importance and relations to the public health; and
to suggest measures by which they can be controlled, if not
exterminated. .

I would take this opportunity of thanking Dr. 8. F. Harmer,
F.R.S., and Mr. W. P. Pycraft for much assistance and advice.

foes AN Do MICE

AS

HNEMIES OF MANKIND

Puates 1 and 2 and text-figure 1 (p. 37), will afford a better
idea of the general outward appearance of the species in question
than would be obtained by reading any detailed description.

lL, RATS: Genus RATEUS:

The two species of rat met with in Britain may be distinguished
as follows :—

1. Rattus rattus. The Buack Rat, House Rat, or SuHip
Rat (Plate 1).

Size smaller ; general build elegant and slender; muzzle sharp.

Ears large, almost naked and translucent, reaching or covering
the eyes when pressed forwards.

Tail slender, at least as long as, and often considerably longer
than, the combined length of the head and body.

Pads of soles of feet relatively large.

Fur soft, but usually intermixed in adults with many slender
grooved bristles, which impart a somewhat harsh quality and
bristling appearance to the coat as a whole.

Teats : the females normally have ten mammae, two pairs on the
chest, three pairs towards the groin ; in some races an additional
pair, making twelve in all, is present upon the chest.

Weight of adults rarely more than 8 ounces, usually less.

Measurements of two adults, in millimetres :-—

Head and Hind-foot, Ear,
Body. Tail. without claws. from base,
188 224 38°6 26

214 252 38 25°95

2 Rats and Mice

2. Rattus norvegicus (“decumanus”). The Common
Rat or Brown Rar (Plate 2).

Size larger; general build heavy and rather clumsy; muzzle
blunt.

Ears small, densely clad with fine and short hairs, thick and
opaque in substance, scarcely reaching the eyes when pressed
forwards.

Tail stout, never as long as the combined length of the head
and body.

Pads of soles of feet relatively small.

Fur softer than in R. rattus, the grooved bristles more slender
and in smaller number.

Teats : the females normally with twelve mammae, three pairs
on the chest, three pairs towards the groin.

Weight of adults normally from 14 to 17 ounces ; but specimens
weighing between 20 and 30 ounces have been frequently recorded ;
one mentioned in the Feld (Sept. 20, 1913, p. 666) is said to have
weighed 2 lbs. 12 ozs.

Measurements of two adults, in millimetres :—

Head and Hind-foot, Ear,
Body. Tail. without claws. from base.
254 222 43 20
267 229 45 20

Good characters for the distinction of the two species are also
afforded by their skulls, which are described and figured on p. 59.

It will be observed that nothing is said about colour in the
above comparison. The reason for this deliberate omission is the
fact that the specific determination of any given rat in Britain
must depend upon the characters mentioned above, and not upon
its colour. Inattention to this point has led many observers into
error ; because most ‘‘ Black Rats’ are brown, and many “ Brown
Rats” are black. Colour only becomes important after we have
determined the species, when it is used to distinguish between the
sub-species or races.

SUB-SPECIES AND HISTORY OF THE BLACK RAT,
, tt. RAP,

Three well-marked colour and pelage phases of this species
occur in Kurope; all three may be found living together in the
same colony, or may occur occasionally in the same litter in

Brit. Mus. (Nat. Hist.) PEATE ts
Economic Ser. No. 8.

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PLATE 2.

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as Enentes of Mankind. 3

colonies of mixed origin; nevertheless, since each has a certain
geographical value of its own, and since each may breed true to
its type, it is not only convenient but natural to regard each as a
distinct sub-species. These sub-species may be defined as
follows :—

1. Rattus rattus rattus. The Black Rat.

Back black; belly smoky grey. Fur on back long and rather
harsh; on belly short, sleek, and adpressed. (This, technically the
type of the species, is essentially characteristic of the cold
temperate countries of Europe.)

2. Rattus rattus alecandrinus. The Alexandrine Rat.

Back brownish grey; belly more or less dingy; dorsal and
ventral colours merging insensibly in each other on flanks. Fur
usually rather harsh on back; on belly usually longer and
rougher than in #. 7. rattws. (Essentially characteristic of Asia
Minor and North Africa.)

3. Rattus rattus frugiwvorus (“tectorum”). The Roof Rat or Tree
Rat.

Back yellowish or reddish brown; belly pure white or pale
lemon; dorsal and ventral tints separated on flanks by a sharp
line of demarcation. Fur very soft and full, with few bristles ;
particularly long and dense on belly. (Essentially a wild-living
rat, inhabiting Sicily, Italy, Spain, and the Mediterranean region
generally.)

All these forms have been conveyed by human commerce to
the various ports of the world. Where they have not had to
compete with native races of Ff. rattus, or with the more formidable
fi. norvegicus, and have met with suitable climatic conditions, they
have frequently established a strong foothold and have colonised
large tracts of the interior.

All forms of R. rattws, whatever may be their colour, seem to
have descended from a bright coloured, soft furred stock, closely
resembling Rf. r. frugiwvorus. Such rats, differentiated into many
local sub-species, abound in India and Burma, and there can be
little doubt that these countries were the cradle of the species ;
there, as in the Mediterranean islands, the white-bellied races are
frequently found living a wild, more or less arboreal, life in the
open country, far away from all human habitations.

4 Rats and Mice

The species does not appear to have been known to the ancient
Greeks or Romans, and although a Roman altar (dating from
100-150 a.p.) in Rheims Cathedral is stated to bear the figure of
a rat, there is no clear evidence of the presence of the species in
western Europe before the time of the Crusades. No doubt the
navies of the Crusaders were largely instrumental in bringing
this animal to our shores. Where climatic conditions permitted,
as in Sicily and the Balearic Islands, the species resumed a
natural life in the open, and it has maintained its primitive wild
coloration.

In cooler countries, or in those with a greater range of
temperature, the species was forced to spend a good deal of time
within doors; in such circumstances it has developed a darker
belly and harsher fur, producing by such means the race called
R. x. alexandrinus. <A parallel change may be studied among
some of the Indian races, notably among those of the Central Pro-
vinces and Kathiawar.

In colder countries, like Britain or Germany, the species was
only able to survive with the aid of the shelter provided by man.
In such regions it has entirely lost its primitive bright coloration
and has assumed the dusky garb of &. 7. rattus. This last change
appears to have been brought about rapidly ; for although the rats
imported by the Crusaders cannot have been any darker than is
R.r. alexandrinus, their descendants by 1530 at the latest, judging
from the descriptions given by Georgius Agricola and by Gesner,
had acquired the full black dress.

Once firmly established in the dwellings and stores of Western
Kurope, &. rattws multiplied to an amazing degree; it became and
remained throughout the Middle Ages, to the beginning of the
eighteenth century, a frightful pest, destroying much property and
food; moreover, the terrible outbreaks of plague, by which the
populations of Hurope were so frequently devastated, are un-
doubtedly to be ascribed to this animal and its parasites.

The arrival in temperate Europe of the Brown Rat, R. norvegicus,
from the Hast, in the early eighteenth century, introduced a new
factor ; a much stronger, more formidable and fecund animal, by
nature used to and fitted for a hard life in a cool country, this
rapidly spread over Britain; wherever it came in actual contact
with &. rattus it killed the latter out, and it speedily, within the
space of fifty years, reduced the range of the weaker species to a
series of isolated and ever dwindling colonies. In this country,

as Enemtes of Mankind. 5

save for the waterside colonies,* continually replenished or re-
established by ship rats, f. rattws appears to have become extinct
shortly after the middle of the nineteenth century. No doubt the
rebuilding of much riparian property, and the gradual substitution of
brick and stone buildings for houses of wood, lath, and plaster,
throughout the country, have contributed largely to the extermina-
tion of &. rattws and to the hindering of its incessant efforts to
re-colonize our land.

In warm countries it has less to fear from the competition of
the Brown Rat, and in many, as in India, it remains the dominant
species. At sea its superior climbing powers give it a great
advantage over the Brown Rat; it therefore continues to be the
principal ship rat. The races frugworus and alexandrinus form a
large percentage of the ocean-going rat population.

COLORATION AND HISTORY OF THE BROWN RAT,
RATTUS NORVEGICUS.

The normal colour of &. norvegicus may be described as
follows :—Back greyish, or reddish-brown, heavily “lined” with
black hairs along the spine; belly silvery grey, but in many
specimens washed with a dingy yellowish-brown.

It is of especial interest to note that this species, although first
established in Britain within the last two hundred years, is already
developing a Black race—described originally from Ireland in
1837 as “ Mus hibernicus.” This black race (frequently confused
with Ff. r. rattus) is becoming commoner and is acquiring a wide
distribution. Should it ever become the prevalent form of the
Species in this country, it would then afford a complete parallel
with R. r. rattus, the evolution of which has been described
above.

The tame rats of commerce are apparently all of this species ;

* One of the best known colonies of &. rattws living in Britain is that
discovered at Yarmouth in 1895 by Mr. A. H. Patterson, who has published
several accounts of it from time to time. Between 1905 and 1910 these rats
increased greatly in numbers and made steady progress through parts of
Yarmouth. With reference to this colony, Mr. Patterson, in litt. (April 1918)
to Dr. Harmer, states that the species ‘‘ which is much harassed now is
becoming rarer. . . . The war allows no grain ships here, so that the species
does not now breed ahead of its destruction. I, however, get three or four
dead ones a week.”’

6 Rats and Mice

by ordinary selection and by Mendelian breeding experiments a
very large number of colour and pattern variations have been
produced. |

The home of Ff. norvegicus is in temperate Asia; according to
Kastchenko the typical form inhabits the territory between the
shores of the Caspian Sea and Tobolsk, while another wild form,
R. n. primarws, is found in the region to the west of Lake Baikal.
No wild representative of the species is met with in any other
part of the continent ; this discontinuous distribution points to the
long standing of the species in Asia.

The ancients may have heard something of the Brown Rat; at
any rate, Adlian’s description of the habits of his ““Mwres Caspi”’ fits
this animal quite well. The people of Western Europe, however,
had no knowledge of the species until 1716, when it was introduced
to Copenhagen as the result of a visit by the Russian fleet (Winge).
In the year 1727, a “mouse year’’ in the Caspian region, vast
hordes of these rats, according to Pallas, moved westwards after
an earthquake (but probably in search of food); they swam across
the Volga and swarmed into the houses of Astrakan. Thence they
spread across Russia into Western Europe.

The species came to England, probably by ships trading with
Russia, in 1728 or 1729; but it is not known to have occurred in
Scotland before 1764. It is said to have reached Paris and East
Prussia in 1750; Norway in 1762 (common there in 1776); the
Faerées in 1768; Sweden in 1790; Spain about 1800; and
Switzerland in 1809. It was introduced to the United States
about 1775, and is now common in most of the thickly populated
parts of America; it is also found in many of the remote districts
of both North and South America. In short, it has now spread
with commerce to all countries. It meets with its chief success as
a colonist in those of a temperate character ; in very cold lands it
is entirely dependent upon the shelter given it by man; and in
warm regions it is frequently unable to displace FR. rattus and its
allies.

GENERAL HABITS OF RATS.

The wide differences in the structure of the two species dis-
cussed in this pamphlet are naturally correlated with some
considerable differences in their habits. Certain habits are, however,
common to both. Thus, both are, in the main, nocturnal or
crepuscular, and they spend much of the day sleeping in warm

as Enemies of Mankind. 7

nests of grass, rags, paper, or other soft materials, placed in their
holes or burrows. Into these retreats they habitually carry much
food, so that when circumstances do not permit of foraging
expeditions (¢.g., during bad weather out of doors, or when danger
threatens within) they are able to remain concealed and secure
for a considerable time. They seek to establish their nests as
near to their food-supply as possible, but often undertake quite
considerable journeys to other feeding places. If the latter are
far from home, temporary hiding-places are usually established ;
and if the new food-supply be attractive, such temporary refuges
may be converted into permanent dwellings and the old nest
abandoned. On their journeys they follow definite paths or runs,
from which they rarely deviate voluntarily. In the open, these
runs are readily found, and may be distinguished from those of
rabbits by the continuously smoothened surface and the spindle-
shaped droppings. In buildings, the runs are no less definite, and
they may be found by sprinkling the floor with powdered materials.
In rooms, they usually keep close to the walls, sometimes on the
floor and sometimes along skirtings or pipes. Rats are extremely
wary, and highly suspicious of traps ; but they may be frequently
caught by unbaited traps, if the latter be properly set in their
runs. While grain may be considered their staple food, they
greedily devour everything edible that comes in their way, be it
animal or vegetable. Like all other rodents, rats have to gnaw
hard substances regularly in order to keep their ever-growing
incisors at a proper length; in default of wood for this purpose
rats will attack all sorts of materials—leather, bone, ivory, lead
pipes and sash-weights, brick, and even cement being among such
substitutes.

&. rattus is essentially an arboreal or climbing animal, and it
rarely burrows; hence, where infesting buildings or huts, it is
found usually in the walls, ceilings, or roof, not in cellars or
drains. Although cautious, it does not shun mankind, and it
enters into far closer relations with its unwilling host than does
the Brown Rat. For this reason it is often the species principally
concerned in the transmission of plague. It drinks little, and
seldom, if at all, enters water voluntarily. As already mentioned,
this is the common rat on ships. In most cases it reaches or
leaves the ships by climbing their cables while they are in dock;
sometimes it is introduced with grain and other merchandise. Its
diet is of a most varied description, but, probably in consequence

B

8 Rats and Mice

of its more salubrious station, it is a far cleaner feeder than
Li. norvegicus. ;

R. norvegicus is essentially a water loving and burrowing
animal; although far less agile than Jf. ratius, it is also a good
climber. As compared with the last named species, it is far more
voracious and cunning; its greater size and strength, and its
much greater fecundity, render it, so far as material prosperity is
concerned, a much more formidable enemy of mankind. On the
other hand, although it spreads many serious or fatal diseases, it
usually exhibits a certain shyness of man, so that, in normal
conditions, it is probably slightly less important than FR. rattus as
a carrier of plague.

It possesses a remarkable power of adapting itself to the most
varied surroundings. Thus, although extremes of heat and cold
are unfavourable to its development and continued success, it may
be found living in many hot countries and also in cold storage
stations. At Tammerfors, a little town of wooden buildings in
western Finland, and a very cold place, it has, according to
Zuschlag, invaded the houses and completely replaced the House
Mouse. Here it has become most impudent and bold; it is to be
found even in the beds of the inhabitants. In such conditions it
must constitute a grave menace to the public health. Again, in
South Georgia it is regularly found out of doors in the summer, living
amongst the coarse tussock grass of that wind- and snow-swept
island, and preying upon the eggs and young of the sea-birds.

The only factor indispensable for the success of this species is
the presence of water; it drinks freely and displays great skill as
a swimmer and diver. Naturally, therefore, it abounds along the
banks of all watercourses ; and these play a great part in directing
and facilitating its advance in a new country, as well as its
seasonal movements or “migrations.” Jt infests sewers and
drains, not only for the sake of the water flowing through them,
but because ordure serves it quite well as food. From such
haunts it readily passes into the basements of buildings, and in
those houses which have their tanks in the roofs it often finds its
way aloft. Where a rat has found such a pleasant and safe
drinking and bathing place it will sometimes visit it with the
utmost regularity for a considerable périod; if living out of doors,
the rat will enter such a house, and leave it again after bathing,
night after night, by a regular run, which may include a long
climb through a stack pipe and a tortuous passage through walls,

NER SF ee ee

as Enemtes of Mankind. 9

partitions and ceilings. Again, attracted by the food of the pit
ponies, as well as by the drainage, rats find coal mines quite
comfortable places to live in; and they often find their way from
one mine to another.

Whenever necessary this species digs with great facility. Out-
of-doors its burrows consist normally of winding galleries, drilled
in banks or hedgerows, and furnished with several bolt-holes. The
burrows are frequently established in soft and warm materials,
such as manure heaps and rubbish mounds; wheat stacks, hay
ricks, and thatch also offer special attractions and are often riddled
with rat holes. It shows a good deal of inquisitiveness, and will
dig out bulbs and roots from garden beds, sometimes, apparently,
merely to satisfy its curiosity. Furthermore, every passing rat
will be attracted by the spoor of its predecessor, so that if one
marauder be caught another soon takes its place.

This species carries out a partial migration at different seasons.
In spring many individuals from farm buildings and towns betake
themselves to the open fields, where they establish burrows and
pass the summer. As autumn advances many forsake the fields
and re-enter buildings for the winter. It is said that in years
with a plentiful acorn crop fewer return to houses and more
remain to pass the winter in the open. The breeding rate, how-
ever, depends upon the amount of food available and upon the
competition for it; the rat population in the buildings is quickly
compensated for the extra number left behind in the fields, and in
the following spring the numbers migrating for the open are not
sensibly diminished. During the ensuing summer the outdoor rat
population rises much above the normal. Similar movements are
connected with periodical changes in food-supply; thus, it is said
that large numbers of rats visit our coast during the herring
fishery, and that they pass inland again in October after this
fishery has stopped. In all these movements waterways of all
kinds, as already mentioned, play a large part. Mr. R. EH. Parker
of Norwich, 2 litt. to Dr. Harmer, says: ‘“‘ Lynn. . . is infested
with rats which annually migrate over W. Norfolk—they are
destroyed in hundreds at Sandringham. We find always that
rats in a dry time in spring return to the rivers and in autumn
they come back up the rivers. You may have a farm clear of
rats one week and well stocked the next.”

Although rats attack and devour such of their fellows as are
injured and too weak to defend themselves, they are normally

B 2

IO Rats and Mice

friendly and sociably disposed towards each other. New-comers
are received as comrades, and if more than three be present in a
cage or sack a man may put his hand in among them and handle
them with impunity. In some circumstances, as when impelled
by hunger, they are extremely bold and will attack man and other
large mammals; they have thus been known to attack and kill a
man who descended into a mine which had been shut down for
ten days, to attack sleeping persons, to gnaw the toes off lepers
too weak to resist, and to mutilate corpses in a mortuary; attacks
upon the feet of living elephants, and upon the ears, backs, and
teats of live pigs are also recorded. Some years ago a large
number of rat-infested houses were demolished in London. As
soon as the buildings were deserted and the food supplies ceased,
the rats swarmed into a neighbouring restaurant; here their com-
petition for food became so keen that they would sometimes jump
upon the luncheon tables, seize and bolt away with morsels of
food from the plates of the customers. In another restaurant
hard by, the writer once saw three rats emerge from a chimney
one after another and jump on to the floor across a large and
fiercely glowing fire; but this was towards the end of the day
when all was quiet.

Rats hunt small vertebrates with great zeal, and sometimes
show such ferocity as to suggest a lust for killing. Young rabbits
in warrens, and the eggs and young of game birds, fowls, and
ducks are frequently devoured. The rat frequently shows the
greatest cleverness in stealing eggs, taking them from under a
sitting hen without disturbing her, or from packing cases without
breaking them, and removing them often over a considerable
distance and many obstacles to the burrow. . Rats soon find their
way to the places where domestic animals are fed, and become
regular visitors; thus, they used to swim across the Regent's
Canal every evening to steal a share of the provisions supplied to
the inmates of the Zoological Gardens.

BREEDING HABITS OF RATS.

Rats and mice are, as is well known, very prolific. They
attain sexual maturity long before they have completed their
growth. Thus, the Plague Commission found the minimum weight
for sexually mature individuals to be at least 70 grammes (about
21 oz.) in fi. rattus (at Bombay), and at least 100 grammes (about

ge ot ee

as Enemies of Mankind. II

34 oz.) in Rf. norvegicus; but the average weight of apparently
adult specimens is certainly not less than 140 grammes (about
5 oz.) in A. rattws, and 250 grammes (about 9 oz.) in R. norvegicus.
“Apparently adult rats” are those in which the coat and colour
are similar to those of old animals, in which the hind-foot measure-
ment amounts to less than 25 per cent. of the head and body
length, and in which, being females, the vagina is perforate; such
rats are certainly at least four months old; growth continues until
they are eighteen months old, and perhaps does not cease then.
De l'Isle, experimenting with f. rattws, found it to be sexually
mature when less than three months old; and EF. Buckland records
that a female Ff. norvegicus in captivity bore a litter of eleven
young when only eight weeks old, so that she must have been
impregnated at the age of five weeks.

Although rats ae in every month of the year, pregnant and
nursing females are more common between the months of January
and June than at other times. Full-grown males, in good health
and normal conditions, appear to be capable of pairing at all times.
The females can only pair at certain times; they have a long
sexual season, extending (for any particular female) possibly through
nine months of the year. During this season they experience
desire, or come on “ heat,” in the absence of the male, at intervals
of about ten days, but “heat” lasts for a few hours only; if not
satisfied it subsides, and the female cannot then be impregnated
until her next “heat.” The period of gestation is normally about
twenty-one days; but if the female be already nursing at the time
of impregnation, the development of the embryos may be retarded,
and the period is prolonged by another ten days or so. During
the sexual season some evidence of the regular recurrence of
“heat” is shown even by the pregnant female; and parturition,
in the season, is immediately followed by ‘“ heat,” so that impreg-
nation is renewed within a few hours of the birth of a litter.

Lataste, to whom primarily we owe a very large share of our
knowledge of the breeding habits of Muridae, found that after
effective coitus the vagina is plugged by a stopper, the purpose of
which apparently is to prevent the escape of semen from the
female before impregnation has taken place. This vaginal stopper
is a joint production of the sexes, its larger, central and quickly
coagulating portion being furnished by the male. The stopper re-
mains in place for some hours, and is then expelled from the vagina.

It may be mentioned here as a point of practical importance

12 Rats and Mice

that, as in other Mirdae, the urethra of the female passes through
the prominent clitoris ; in mature does, the vagina is a conspicuous
orifice between the clitoris and the anus; but in immature females
the vagina is sealed and quite invisible externally, and such
specimens can frequently be mistaken for males; distinction by
mere inspection is, however, possible, because the distance
between the clitoris and the anus is less than between the penis
and the anus.

The number of litters per doe per annum and the number of
young per litter are dependent upon many factors, of which the
most important are food supply, the age and condition of the female
pairing, and, in a much lesser degree, climate and temperature.
Lt. rattus probably shows a higher fecundity in warm temperate
countries than in cold temperate lands; &. norvegicus, on the
other hand, is more fecund in cold temperate climates. Increased
nutrition not only leads to larger and more frequent litters, but it
almost certainly results in decreasing the mortality among very
young rats. Although very good and careful mothers, as a rule,
female rats eat their offspring in certain conditions, such as when
overcrowding leads to disturbance or to too keen competition for
supplies. In Newton Miller’s experiments with ft. norvegicus in
captivity 50 per cent. of the young born were thus devoured.

The embryos of the pregnant females among 12,000 rats
trapped at Bombay were counted, with the following results :—

R. rattus. KR. norvegicus.
Average number of young per litter 5°2 8:1
Maximum number of young per litter 9 14

In Europe £&. rattus is described as bearing from four to
eleven young in a litter; probably the normal number per litter
in Britain is between six and eight.

As regards f. norvegicus, twenty-three litters examined iy Mr.
A. H. Cocks, at Great Marlow and Poynetts, Bucks, gave a range
of from six to twelve per litter, the average number being nearly
eight per litter. This may perhaps be taken as a measure of fecundity
in rural conditions.* But much larger litters are frequently observed,
particularly in towns. Litters of seventeen, nineteen, twenty-two,

* Between January 16 and February 14, 1911, Petrie and Macalister
examined 6,071 specimens of R. norvegicus collected in Suffolk and Essex
during the period specified; of these 3,273 were males, 2,724 females, and of
74 the sex was not recorded : 290 or 10°6 per cent. of the females were
pregnant, the average number ‘of foetuses being 9 (7, p. 60).

2.

as Enemies of Mankind. 13

and twenty-three have been recorded; and Lantz thought it safe
to conclude that the average is not less than ten per litter. Newton
Miller’s experiments gave an average of between ten and eleven,
the number per litter ranging between six and nineteen; his
evidence also showed that the females produce five or six litters
annually.

The young are born in a helpless condition, being blind, naked
and pink, with their external ears sealed down. Their eyes open
at about the fourteenth day, and they are weaned in the course of
their fourth week.

THE ECONOMIC IMPORTANCE OF RATS.

We have now to consider rats from an economic standpoint.
In such discussions we usually find two sides to the account—
credit and debit. Unfortunately there is practically nothing that
can be placed to the credit of either Ff. rattus or R. norvegicus.
Their activities as scavengers are no longer of the slightest benefit
to humanity ; the most that can be said for either perhaps is that
they may keep the numbers of House Mice to some extent in check.
On the other hand, the debit account is long and deplorable.

Damage occasioned by rats.—That rats do great damage
to property and materials of all kinds is a fact only too well
known to the public. Therefore, there is no need to review in
detail all the misdeeds of these animals; we may be content with
mentioning some of the chief heads of damage.

Property.—By burrowing under foundations, through walls
and embankments, and by gnawing their way through partitions,
doors, and joists rats cause great damage to property. Such
operations have sometimes led to serious structural collapses and
considerable monetary loss. By gnawing through gas and water
pipes they occasion great inconvenience and sometimes serious
danger; by carrying matches into their combustible nests and
igniting them, and by gnawing away the insulation from electric
lighting wires, they have caused destructive outbreaks of fire and
sometimes the death of the human residents.

Materials and Food.—In docks, warehouses and shops, and
while in transit by rail or sea, large quantities of merchandise, of
the most varied description, are annually destroyed or more or
less seriously damaged by rats. In houses, hospitals, and other
institutions they display a most catholic taste—food, furniture,

1A Rats and Mice

books, linen, pets, and sometimes man (alive and dead) being
attacked.

To agriculture in all its branches the Brown Rat is especially
a most dangerous pest. Grain of all sorts is undoubtedly the
chief and favourite food of the rat. Before the grain is sown, in
every stage of its growth, and after the harvest, wherever it is
stored or in whatever form it is used, it is subject to attack by
this animal. An enormous toll is thus levied upon farmers,
millers, grain merchants, and consumers—-a toll which is difficult
to appraise, but which, in the case of the farmer, must often be
equal to rent and taxes combined. People who keep animals for
profit or for pleasure sometimes feed, regularly if unwittingly,
some hundreds of rats in addition to their stock. Poultry farmers,
breeders of game-birds, pigeon fanciers and others suffer great
losses in this way ; what is worse, their eggs are regularly stolen,
their young and even their old birds are attacked and killed. Pigs
and other large animals are often destroyed, or rendered worthless,
either by reason of deliberate attacks upon them made by rats, or
through coming in contact with or devouring rats or food con-
taminated by the latter. In warrens, large numbers of young
rabbits are destroyed. Great havoc is sometimes wrought among
root-crops, dnd all kinds of fruit and vegetables are greedily
devoured.

In short, every description of food for man or beast, whether in
course of production, store, or use, is subject to the attacks of the

rat. The quantity actually eaten or carried away is very consider- .

able, but far more is ruined than devoured; and when food, rat-
tainted though still wholesome in appearance, is used it sometimes
entails * disastrous consequences to the health of man or that of
his domestic animals.

Such damage is not confined to Britain; it is caused through-
out the world wherever the Brown Rat has gained a footing. In
favourable circumstances rats multiply with amazing rapidity, and
they speedily bring utter ruin and devastation in their train. Two
small instances of this may be quoted. Deget is a small island in
the Cattegat. According to Zuschlag, the rat was quite unknown
there until two boys introduced a pair of tame rats, which they
had purchased in Jutland. These pets escaped. In less than two
years their progeny became a plague infesting the whole island
and succeeded in exterminating the numerous birds, which until
the establishment of the rats in such numbers used to breed there.

tb Aad a? ert NS ‘

as Enemies of Mankind. 15

The second case is that of Lesser Cumbrae, an island of 900 acres
in the Firth of Clyde. According to Boelter (quoting from
Chambers’ Journal) rats had been known on the island for a
number of years, but they seem to have given no particular
trouble. Then a French ship was wrecked and its rats made their
way to the shore; they multiplied at a tremendous rate, and in the
course of four years developed into a serious plague. In 1907 the
keeper lost five tons of turnips; at Christmas the rats attacked,
killed and devoured a 20lb. turkey. The rabbits, rose bushes, wild
duck, mangolds and woodcock inhabiting the island were
threatened with extermination. At last virus was used (this time
with success, be it noted) and the rats succumbed.

Various estimates of the value of the damage caused by rats to
property and materials in Britain and other countries have been
published. Quite apart from the difficulty or impossibility of
obtaining accurate information as to the number of rats inhabiting
any given country, it is most difficult to estimate the loss. On the
one hand, although rats consume and spoil vast quantities of food
and materials, both in course of production and in store, they also
eat much matter which is purely waste. And further, while in
some cases the damage done is promptly detected and recognized
as being due to rats, and the loss occasioned has a definite
measure, in the majority the damage is done unobtrusively and
silently to things which are developing and of which the value has
not been ascertained. The loss is often gradual and not easily
detected (as when food is stolen from the supplies of domestic
animals); but it is continuous and soon totals up to a large sum.

To the actual damage caused by rats we have to add the large
sums which are annually expended by public bodies, companies,
and private individuals on rat-catching operations. According to
Boelter, the capital employed in this country in providing rat-
catching or rat-killing apparatus had grown to £2,000,000 in 1909.

Boelter assumed the rat population of Great Britain to be
40,000,000—.e., about one to each acre cultivated, or one per head
of the human population. He further assumed that each rat on
an average occasioned a daily loss of one farthing; on these
assumptions, the total annual damage done by rats in this country
amounts to £15,000,000. This estimate does not take into account
the damage done by rats on our ships; it relates solely to the rural
and urban activities of these animals. The estimate received the
approval of Sir J. Crichton-Browne, and enquiries made of a very

16 Rats and Mice

arge number of the people who throughout the country are
brought most closely in contact with the rats, elicited the fact
that none thought either of Boelter’s premises excessive, while
many thought them too low. Dr. Shipley, on the basis of a
similar assumption as to the size of the rat population, estimated
the annual damage in Britain at £10,000,000.

On a later page (p. 60) a table dealing with the rat population
of Britain and its expected increase in the current year is given.
On the basis of that table we have endeavoured to estimate the
minimum loss which will be inflicted upon us this year by rats.
In these calculations we have assumed an excessive mortality and
waste among the rats; we allow nothing at all for the mainten-
ance of rats not yet capable of breeding; and we suppose that they
will not breed until they are four months old. The cost of main-
taining the breeding stock is assumed to be no more than one
farthing a day for each rat, but the sum works out to a total of
£9,224,000.

In other countries the annual loss attributable to rats has
been estimated similarly to reach huge totals. In Denmark it is
said to amount to 15,000,000 franes ; in France the loss occasioned
in 1904 was estimated at 200,000,000 francs; the loss in Germany
is officially estimated at 200,000,000 marks; and in America the
Biological Survey estimates that the direct annual loss sustained
by residents in the towns and cities of the United States amounts
to 20,000,000 dollars, while the total annual damage inflicted
throughout the United States is put at 200,000,000 dollars.

RATS IN RELATION TO DISEASE.

However estimated, the financial loss occasioned by rats, in
wasting our food, materials, and property, must appear colossal.
But that loss sinks to insignificance when we consider how grave
is the risk of disease entailed by the presence of these pests in our
midst. The financial loss directly affects, perhaps, only a com-
paratively small number of people, and many of these, ignorant of
its extent, are quite indifferent to its cause. The menace to health
is real, and it affects every member of the community. In spite
of the excellent and unremitting efforts of our Public Health and
Port Sanitary Authorities, that menace will last and will grow
steadily so long as there is a large and increasing rat population in
this country. The list of diseases disseminated by the rat grows

as Enemies of Mankind. 17

as biological and medical studies proceed. In this place we can
discuss only a few of them, but the few will suffice to prove that,
even in these days, humanity possesses no more deadly enemy
than the rat, and that the rat problem is as serious and urgent as
any before the public at present. Whatever the cost in labour or
money may be, the extermination of the rat is a necessary step for
the public safety.

Plague.—The great tragedies wrought by this disease in
Western Europe, from early medizval times down to the begin-
ning of the last century, are familiar to all. Plague is by no
means extinct. During the last twenty years it has killed millions
of people in various parts of Asia; from the Hast it has spread
and is still spreading to all quarters of the globe. It shows every-
where a virulence of type which augurs ill for Europeans should
they fail to keep the disease under control. In almost each of the
last ten years several deaths have occurred in Great Britain.

Plague is a disease of the circulatory and respiratory systems
resulting from an invasion of the body by a minute organism, the
Bacillus pestis. The disease exists in two forms, viz., Bubonic
plague and Pneumonic plague; these differ merely in their mode
of infection and symptomatically. In bubonic plague the blood is
infected ; typically, the bacilli are arrested in the glands, which
swell into buboes and suppurate. In more acute cases the glands
fail to arrest the bacilli, and the battle between the latter and the
phagocytes is fought out in the blood, giving rise to what is called
“septicemic plague.” In pneumonic plague the pulmonary
organs are infected with the bacilli, and the ensuing symptoms
closely resemble those of pneumonia. In either form the disease,
in the majority of cases, terminates fatally.

This dreadful scourge belongs essentially to rats and the
peculiar species of fleas infesting them; it is Nature’s unfailing
method of periodically reducing the rat population to reasonable
proportions. The rat fleas feed on the blood of an infected rat ;
at one meal a single flea can take with this blood as many as
5,000 plague germs into its stomach. Bacillus pestis multiplies
in the stomach of the flea rapidly—so rapidly that an obstruction
is often formed in the alimentary canal of the flea near the
entrance to its stomach. Such a flea grows hungry, in due
course, and endeavours to feed; but although it can still pump
blood from its host, the obstruction in its gullet prevents it from
swallowing, and so the blood is forced back into the wound; the

18 Rats and Mice

mouth of the flea becomes contaminated and infested with plague
germs. In due course the plague-smitten rat dies, and its fleas
have to seek other hosts. If another rat presents itself, the fleas
collect on it. The “hungry fleas” at once attempt to feed; they
bite and pump blood again and again, each time forcing con-
taminated blood back into the system of the new host. The
latter is speedily infected with plague; and so the disease goes on
spreading in an ever-widening circle, and a great mortality ensues
among the rats.

Rat fleas carrying plague germs do not, unfortunately, always
select another rat as the successor of their first host. They often
collect on other rodents, and they have been known to infect
horses, dogs, and pigs. But very often man himself is the new
host, and a single germ is sufficient to infect him with plague.
In man such an infection always takes the form of Bubonic
Plague. This is not contagious; it can only be transmitted to
man by a direct blood infection, as by the bite of rat fleas. Ata
later stage, however, plague becomes more virulent among
humanity; it develops into Pneumonic Plague, which is highly
contagious. Unless checked, it now becomes epidemic and spreads
death on every hand among the unfortunate people attacked.

Often the advent of plague among people is heralded by a
noticeable mortality among the rats; but this is not invariably
the case, for men are sometimes attacked before the disease has
made any visible strides among the rat population. Plague is
quite frequently detected among the rats in British ports; it is
constantly arriving in this country, and every year deaths from
it occur among the human inhabitants. In East Suffolk, between
the Orwell and the Stour, plague seems to be endemic among the
common rats; several human deaths from pneumonic plague have
occurred at various localities there in recent years. These cases
have recurred after intervals of many months, and in spite of the
most active and careful preventive measures known to sanitary
science. They serve to show that plague, once firmly estab-
lished, is most difficult to eradicate, and to warn us of the fact
that we can afford to take no risks in this matter.

Trichinosis.—Rats and mice are the principal agents con-
cerned in disseminating and perpetuating this disease. The cause
of trichinosis is a very remarkable parasitic worm, Trichina spiralis.
Large numbers (often millions) of immature Trzchina are sometimes
found embedded and encysted, in calcareous envelopes, in the

pipe:

as Enemies of Mankind. 19

muscles of mammals and birds. Individuals so infested by the
parasite are said to be trichinous; the common rat, the pig, and
man share the unhappy distinction of being the species most
frequently infested. While encysted the immature Trichina
remain in a state of suspended animation, and are therefore
incapable of further development. This inertia, which may last
for many years, is only overcome if and when another warm-
blooded vertebrate devours a portion of the trichinous flesh. In
the course of digestion the gastric juices dissolve the calcareous
cysts and the young T’richina emerge in the bowel of their new
host. They now grow rapidly and perfect their sexual organs.
The sexes are distinct, the males being smaller than the females.
This development takes three or four days; within a week the
Trichina are fully adult, and pairing takes place. The females
carry enormous numbers of ova (1,000 to 15,000) ; after fertilization
these develop and are hatched within the body of the mother,

the young being eventually brought forth alive. Young Trichina

begin to appear in the intestine at about the eighth day after
infection ; they at once migrate by perforating the walls of the
alimentary canal and the abdominal cavity, and so find their way
into the muscular tissue, where they encyst themselves. The
migration takes about ten days, and the encystment commences
in about fourteen days. Each young Trichina, as a rule, forms
its own cyst; but sometimes cysts containing two, very rarely
even three, of the worms are found.

Such is what may be termed the normal life-history of this
parasite; but of the large numbers sometimes liberated in the
bowel on infection, and of the enormous numbers born subsequently,
a certain proportion usually escape from the alimentary canal of
the new host with the feces. An animal feeding upon such
trichinous excrement will also be infected.

Man is infected by eating trichinous pork, particularly when
raw or only partially cooked. In spite of microscopic examination
of carcases, it is impossible in practice to guarantee that any given
pig is absolutely free from encysted Trichina, and as a matter of
precaution every particle of pork should be thoroughly cooked
before being eaten. No less than 32 per cent. of the German
cases, between 1881 and 1898, were traced to pork officially in-
spected and passed as being free from this parasite. Trichinosis
in man is a very serious malady. Infection is followed by nausea,
loss of appetite, diarrhcea, and fever; later, when the young

20 Rats and Mice

Trichina are born, and their migration commences, there is further
fever, exhausting diarrhoea, and much pain and swelling in the
muscles. The chance of surviving infection depends upon the
vitality of the patient and the extent to which he is infected. If he
survives the migration and encystment of the young Trichina he
will be safe, since the parasites now become inert, but he may feel
bad effects from their presence for many years. Mortality in cases
of trichinosis is high; in one instance a single pig, converted into
sausages, caused 337 cases of trichinosis, and of these 101
terminated fatally.

The pig is infected with Tirichina by devouring the bodies of
dead rats and mice, or food fouled by the excrement of these
animals. The Common Rat is the chief host of the parasite; the
latter is, however, not uncommon in the House Mouse. Rats and
mice devour the bodies of their fallen comrades; they do not
despise food contaminated with their droppings; and rats feed
upon the dung of other animals. Further, in slaughter-houses,
rats often have an opportunity of feeding upon the trimmings from
trichinous flesh ; in Glasgow City Abattoir 3 per cent. of the rats
were found to be trichinous. In these various ways these rodents
ensure the continued existence, abundance, and wide dissemination
of 7. spiralis.

Sokodu, or Rat-bite Fever, results from infection ensuing
upon the bite of a rat. The wound is said to heal rapidly and
apparently normally, but after an incubation period, varying from
a few days to a month, it becomes inflamed and painful. This is
followed by rapid variations in temperature, and symptoms of
serious systemic infection; the kidneys in particular are badly
affected. Death may occur from nephritis, or from exhaustion.
If not immediately fatal, the disease assumes a relapsing form ;
its course may extend over several months. In one case it
developed into a progressive wasting with recurrent fever lasting for
eight years. (or further details and treatment see Longman, p. 26.)

Influenza in an acute form occurs among horses, and it is
conveyed from stable to stable by rats. Where the outbreak of
the disease has led to the closing of a stable, the disease usually
appears promptly in the other stables of the neighbourhood,
because the rats migrate from the closed stable so soon as their
food supply stops. An even more striking illustration is afforded
by the outbreaks of equine influenza among the ponies of adjoining
coal mines.

as Enemies of Mankind. 21

Similarly, foot-and-mouth disease and dysentery are now
known to. be carried by rats.

Finally, the Common Rat makes its way into the store-places
and kitchens of our houses and restaurants. Into these places,
besides contaminating our food with its own germ-laden dejecta
and parasites, it brings a wealth of indescribable filth from its
favourite haunts in the adjoining sewers and drains. At this point
one may leave the reader to his own reflections.

THE POSSIBILITY OF THE EXTERMINATION
OF RATS.

Having thus described some of the evils resulting from the
presence of rats in Britain, we proceed next to consider the size of
the rat population, its natural increase, if any, and the prospect
and means of controlling it successfully in future.

There have been many attempts to calculate the reproductive
potential of rats. For instance, F. von Fischer, in 1872, concluded
that the progeny of a single pair might in ten years amount to no
less than 48,319,698,843,030,344,720 individuals. Rucker, more
recently, has computed the increase of a pair in five years at
940,369,969,152 rats.

Lantz was not so ambitious; for the purposes of his calcula-
tion he assumed the rats to breed only three times a year, and
to have average litters of ten. Breeding at this rate uninterruptedly
for three years, producing sexes in equal numbers, and with no
deaths, the progeny of a single pair at the ninth generation would
be 20,155,392 rats.

Zuschlag assumed a pair to have six litters of eight in a year;
that the young would breed when 31 months old, then with equal
sexes and no deaths the progeny at the end of the first year would
be 880 rats.

Although such calculations are purely theoretical, and although
their results, in ordinary circumstances, will never be approached
in Nature, they are not extravagant, gua the power to reproduce,
but are based upon moderate and conservative estimates. In
proof we may cite Kolazy’s record that two females kept by him
had twenty-six litters in a space of thirteen months, and produced
180 young—almost double the number assumed by Zuschlag. We
can, therefore, readily understand how the progeny of a few
rats introduced to a new country by a ship may, in favourable

22 Rats and Mice

circumstances, succeed in overrunning the whole country in the
space of a very few years, and how these animals speedily develop
into a most serious pest when what may be called the rat resistance
of a country is allowed to sink to a low degree.

In 1909 Boelter, after a long series of enquiries, assumed the
density of the rat population to be not less than one rat to each
acre cultivated, or alternatively one rat per head of the human
population. The minimum number of rats inhabiting Britain was
therefore put by him at 40,000,000. In the opinion of many,
including the present writer, that estimate is a very low one.

Between 1909 and 1916 energetic efforts for the destruction of
rats were made by many public bodies and companies throughout
the country. One metropolitan body, for instance, by trapping
and other means, destroyed in 1911, 9,936; 1912, 10,834; 1913,
13,781; 1914, 12,616; 1915, 11,272; and in 1916, 15,123 rats ;
in addition many others not identified must have been destroyed
by the official cats kept.*

The returns published in respect of rats killed in the City and
Port of Liverpool afford similar reading. Here again—and
numerous other instances could be quoted—the numbers of rats
killed from year to year increase rather than diminish. In purely
rural districts it is similar: thus in Hast Haddington the efforts of
the Hastern District Committee of the Haddingtonshire County
Council resulted in the destruction of rats as follows :—

For the year ending Oct. 25,1913. . 20,798
is is 24,1914 . . 23,625
* is ris Bs AP Baan . 25,636

* Dr. Willoughby has records of the destruction of 931,846 rats between the
years 1901 and 1916; this number includes rats killed during the voyages or
on the fumigation of vessels entering the Thames, as well as those killed in
docks and warehouses. He says (in litt. to the writer) :—‘‘ I am not aware of
increase [in rat population] in any part of the Port Sanitary District, but
suspect it in a few food-store localities which have come into use since the
war... .I suspect that the Brown Rat is found in less numbers than the
Black in certain docks, which I recognize as storage or warehouse docks (as
opposed to transit docks), from the fact that a larger number of Black than
Brown are brought for examination from these docks. Im one dock the
proportion of Brown to Black brought for examination in 1916 was Brown
1,265, Black 90; in another, Brown 249, Black 311. In the one dock the
‘wild’ and ‘transit’ conditions prevail, in the other the ‘warehouse’ and
‘domestic’ conditions. In the one are grass banks (for summer burrowing)
and one-storey sheds; in the other granite and warehouses. In the Blacks of
the above figures I have included rattus and alexandrinus (a fair sprinkling of
the latter are reported).”

as Enemies of Mankind. 23

This last case is especially instructive because the extent of
the means of destruction employed, as well as that of the area of
operations, has remained constant during the three years covered.
If now we may take the number of rats killed as an index of
the number of rats living, then we may conclude from such
returns that the measures adopted for the destruction of rats up
to and including the year 1915 have not resulted in bringing about
any absolute decline in the rat population; in fact, the figures
suggest that destruction has not even been able to keep pace with
the natural increase of that population.

Now, although the war has rightly not been allowed to interfere
with the catching of rats in our chief ports, because of the
paramount importance of protecting the public health, it has most
seriously interrupted and discouraged such work in ordinary
towns and in the rural districts. Military service, the manufacture
of -munitions, and the great rise in wages in the towns have all
contributed to denude the country and the towns of that labour
which was formerly devoted to rat extermination. The need for
enforcing economy in the use of foodstuffs has given rise to a
series of regulations, which in effect prohibit the use of all food for
bait, and for conveying poison or virus to rats. Such regulations
also have therefore played a great part in obstructing or stopping
the indispensable work of the rat-catcher. The result is deplorable.
From all parts of the country come complaints of a great increase
in the numbers of rats present, and of the great damage they are
doing to ordinary agriculture as well as to the produce of the
allotment holder. Such a result was bound to ensue, even if
nothing had been done to assist the rats beyond the temporary
cessation of our efforts to destroy them. But the great national
endeavour to increase the internal sources of food has benefited
rats as well as citizens. The numbers of rats, no less than the
numbers of men, depend entirely upon the food supply; and as
all classes have become or are becoming producers of food, so in
proportion the capability of the country to support rats has grown
and will grow. Every new allotment, new chicken-run or rabbit
hutch, offers a new niche in Nature for the accommodation and
maintenance of the rat. As is shown in the following paragraphs,
the rats not only are able to, but must take advantage of these
new outlets for their numbers, for with them it is a case of colonize
or perish. For our safety it is imperative to find a means of
controlling the rat population.

c

24 Rats and Mice

What is the problem to be faced ? In order to express it in the
most moderate terms possible, let us assume that the rat population
of this country on Jan. 1, 1918, was still no more than 40,000,000—
that is to say that Boelter’s estimate of 1909 still held good at the
date in question in spite of the lapse of nine years and in spite of
the unfortunate events of the last three years. Let us assume
the sexes to be equally distributed. A certain proportion of the
40,000,000 rats will, from one cause or another, have no chance of
breeding, and may be thrown out of our calculations at once. Let
us assume that 50 per cent. have to be so discarded. That leaves
us with 20,000,000 rats, or 10,000,000 pairs, on Jan. 1, 1918, as
our capital stock with a chance of breeding. But even breeding -
rats must die; we will therefore assume that 95 per cent. of our
10,000,000 pairs will die, by equal monthly instalments, in the
course of the year. We have thus assumed a natural mortality and
waste among the rats amounting to a total of 97:5 per cent. per
annum ; and by this assumption we have reduced our initial stock of
40,000,000 rats to 1,000,000 in the space of twelve months. This
waste is repaired by breeding. Let us assume that each pair of
rats, surviving long enough, has six litters per annum, and that
each litter contains on an average eight young. As will be seen
from the account of the breeding habits given above, both these
assumptions are moderate. A certain number of young will die
at birth; we will assume that this accounts for 50 per cent.—a high
proportion. Of the survivors, many will never have a chance of
breeding ; we will assume this to apply to 50 per cent. of them, or
to 25 per cent. of all born. Those that have a chance of breeding
have also to die; and as in the case of their parents, we will
assume that natural mortality accounts for 95 per cent. of these
effective rats, and we will reckon it from the moment of their
birth. Here again we assume a huge waste and mortality
probably much in excess of the natural waste. The young rats
are assumed to breed first when four months old and at the same
rate as their parents; and the assumptions made above are also
made in the case of succeeding generations.

In the accompanying table (p. 60) the results of the calculations
based upon the above assumptions are given, so far as they
concern the effective or breeding stock of rats. From this table it
will be seen that our effective capital stock of 10,000,000 pairs on
Jan. 1 might be replaced on Dec. 31, 1918, by no less than
41,000,000 pairs, and that in the early days of January, 1919, we

as Enemies of Mankind. 25

might expect the birth of 12,000,000 pairs possessing a chance of
breeding. Further, although it would considerably affect the
calculations if they were extended to cover the year 1919, the
assumption of three instead of six litters would make comparatively
little difference to the figures given for 1918; our 10,000,000 pairs
of Jan. 1 might still grow to 32,000,000 by Dec. 31; the cost of
keeping them, estimated at £9,224,500 with six litters, would only
be reduced by £232,500 if we assumed the birth of the first three
litters only.

Such a calculation, although open, it is true, to many objections,
suffices to prove that we are dealing with a very formidable
problem indeed. Such a rate of increase must very soon lead
to disaster if it be not checked; it cannot continue. In normal
conditions Nature would and does step in to check it. The
natural enemies of the rat—carnivorous mammals, such as weasels,
stoats, polecats, martens, cats, and foxes; birds of prey like owls
and kestrels; reptiles such as snakes—these, with their food-
supply so greatly increased, would multiply in proportion. If, in
spite of the havoc wrought by these carnivorous creatures, the
numbers of rats continued to increase unduly, Nature’s other and
more dreadful remedy would assert itself. Food and space are
limited ; underfeeding and overcrowding would sap the vitality of
the rats; the weaker individuals would be attacked by micro-
organisms, Bacillus pestis, and innumerable others ; their stronger
brethren would in turn become infected, either by devouring the
bodies of, or by receiving parasites from those that succumbed.
Pestilence would break out in this way among the rats all over the
country, and it would in a very short time reduce their numbers
to insignificance.

So much for normal conditions. One of the’ penalties of civili-
zation is that we deprive ourselves of the assistance of most of our
carnivorous allies. Polecats and martens have practically gone,
and wild cats with them; domestic cats as a class are not keen
on ratting, though there are exceptions; foxes are too mischievous
to poultry, and their numbers are strictly limited; weasels and stoats,
which do an invaluable service in killing large numbers of young
rats (and it should be recognized that young rats are always more
numerous and potentially more dangerous than adults) are every-
where persecuted ; owls and kestrels are too frequently shot at sight ;
and snakes no longer count. We have, it is true, our domestic dogs
and ferrets. Working with an experienced man, these do a great

Cc 2

26 Rats and Mice

execution among.rats ; but their powers have limitations, and they
form no sort of just equivalent for the wild carnivora we have lost.

Even if we still possessed our full quota of carnivorous creatures,
it is more than doubtful whether that would relieve us from anxiety
in this matter. Our enterprise in engineering and building has
provided the rat with a measure of shelter and security infinitely
greater than the best that could be afforded it by Nature. Against
rats in such strongholds carnivora could do but little.

We cannot, however, deprive Nature of her second weapon:
infectious disease is always present, if latent, among rats as among
men. But we dare not let Nature invoke disease; for should she
do so, that disease will in all probability smite man no less than
the rat. For this reason our public health authorities work hard
to preserve the rats in good health. As soon as they observe
mortality from unknown causes among rats they look for plague ;
if, as often happens, they find plague, they endeavour to protect
the rats of other places by first isolating and then exterminating
the infected colony. Biology has sought and is still seeking a
disease which will kill rats but be harmless to man and his
domestic animals ; that search has not yet been rewarded, although
results of great promise have been obtained. Promise is one thing,
fulfilment another; the disease weapon to our liking may not be
fashioned before we have felt the sting of one of those already
existing in the armoury of Nature.

What then is to be done? Are we so destitute of resource that
we must be content to wait for that punishment inevitably ours if
we do not find a method of redressing the balance of Nature so
light-heartedly disturbed? The answer to the latter question is
simple. Although there is no royal road to such an end, we
possess ample means of exterminating the rat if we have the mind
to do so. These means, however, will not avail until everybody
in this country is convinced of the necessity of using them
whenever and wherever possible. There are six indispensable
co-efficients upon which the success of whatever means we may
adopt will depend; these are organization, co-operation, deter-
mination, time, money, and labour—the way of the transgressor is
hard. Of course, science may shorten the road for us, but not
without further biological research of all kinds. That, however,
again costs time and money; and so many have yet to learn that
all branches of science are valuable and interdependent, that in
reality there are not two kinds of science—one called ‘ applied,”’

as Enemies of Mankind. a7

essential, it extracts gold; the other called “pure,” quite unim-
portant, it extracts nothing but facts.

The need for organization and co-operation in rat destruction
will appear from the following remarks. The table at p. 60,
be its figures right or wrong, fairly illustrates the working of the
principle by which the rat population increases in spite of the
enormous toll occasionally levied upon it by man. Many more
rats are born than can possibly survive; many more survive than
can possibly breed. If A has premises, which cannot be or have
not been rendered absolutely rat-proof, in a rat-infested area, it is
perfectly useless for him to kill rats without the co-operation of
his neighbours B, C, and D; the utmost reward for his trouble
and expense will be a little temporary relief. For in exterminating
his own rats he has created a vacancy for a corresponding portion
of the surplus rat population born on the property of his negligent
neighbours, and accordingly, in a very short time, A will acquire
a new stock of rats. A good instance of this is given us by the
officials of one of the great trading corporations of London. They
say that, in consequence of their unrelenting persecution and
continuous efforts to abolish all shelter for rats, comparatively few
of the animals are able to breed upon their premises ; in some of
their warehouses the numbers of rats caught tend to diminish from
year to year, in others they increase. They ascribe the increased
numbers to the action of certain local authorities, who permit large
rubbish dumps to be formed on lands adjoining the premises in
question. In these dumps rats breed in enormous numbers, and
for the most part they visit the warehouses merely in search of
food. ‘Trapping in these places on a large scale no doubt saves
considerable losses of stores, but as regards the rat population its
only effect is to give a chance of living and breeding to many
individuals who otherwise would not have possessed such a chance.

Further, the County Medical Officer of Health for Hast Suffolk,
reporting upon the steps taken by the county, urban, and rural
district councils in regard to the outbreak of rat-plague, says :—
‘From all parts of the county we hear of the active work under-
taken by private individuals. A large amount of time and money
has been expended by them in the destruction of rats. They
make one complaint, a very pertinent one; it is that their work is
of small permanent avail because of the apathy of their neighbours,
and this indifference is to be found in the close proximity of, and
even within, the areas where the infected animals have been found.

28 Rats and Mice

This want of unanimity of action is much to be deplored, and is
very unfair to those who have willingly expended much.” (7,
p. 84.)

Such facts lead us to conclude that spasmodic, individual, or
purely local attempts at rat extermination can bring no real relief.
The work of destruction, to succeed, must be undertaken simul-
taneously all over the country; it must be systematically done
with the approval and co-operation of all; and it must be
continued so long as a breeding stock of rats remains in this
island. The last point is of essential importance. It may be said
at once that the final stage of such a war on rats will be the most
difficult and, in visible results, the least spectacular of all; but a
premature cessation of our destructive efforts would be followed
by a speedy recurrence of the present evil; our money and labour
would have been expended in vain.

It is, of course, not within the province of the writer to suggest
the means by which a work of such magnitude and importance
can be organized or financed, nor how general co-operation can
be secured; those are questions entirely for the public and Parlia-
ment. The writer has performed his duty by pointing out the
urgent necessity for some such action against the rat population ;

these animals are at once a reproach to civilization and a menace
to humanity.

RAT-PREVENTION AND RAT-EXTERMINATION.

The country owes its rat population in the first place to the
ports. The ports and the towns feed the rural districts with rats ;
waterways form natural high roads for rats; human traffic, water-
borne and land-borne, greatly assists their dispersal. The key to
the problem lies in our towns, for the rural districts can never be
kept permanently free from rats while the towns are infested.

The problem is, however, most difficult of solution in the
towns; because here the rat population attains its maximum
density, and finds food and shelter in abundance. Here also our
choice of means of destruction is limited practically to traps and to
attacks with the help of dogs, ferrets and cats; poison and virus,
because of the danger to health which their use involves, can be but
seldom used in towns. Preventive measures must play the chief
part in towns, active destruction, although most useful when com-
bined with prevention, being quite unable to eradicate urban rats.

The chief Preventive Measures are :—

as Enemies of Mankind. 29

1. Protection of food supplies.

This is of prime importance. All foodstuffs in stores, markets,
and shops should be kept in rat-proof receptacles when not
exposed for sale. Household larders and the mangers of domestic
animals should be carefully protected from rats.

2. Removal and destruction of refuse.

Pending removal, all refuse should be placed in rat-proof
receptacles, such as metal bins with tight-fitting lids. Our care-
lessness in this matter provides nourishment for swarms of rats
in every city.

Refuse should be promptly removed and destroyed. The
formation of rubbish dumps is a most dangerous practice and
should be prohibited ; such dumps always afford good shelter and
much food to rats; and they frequently become the principal
breeding places and strongholds of rats infesting docks, ware-
houses, and railway goods yards.

3. Rat-proofing of buildings.

All new buildings should be made rat-proof by the liberal use
of cement in their cellars and foundations, and by the proper
protection of their doors, basement windows, ventilators, and
drains. Whenever opportunity presents itself similar protection
should be given to existing buildings.

4. Protection of drains.

All drains opening into sewers should be efficiently sealed.
Inlets and outlets of stackpipes, etc., should be guarded with
wire cages.

5. Fumigation of ships, and protection of quays, rail-
ways, etc.

In most ports the Sanitary Authorities now fumigate ships and
take steps to prevent rats from passing from ship to shore and
vice versa.* The importance of such measures cannot be exag-
gerated, and it is to be hoped that everything will be done to
extend or improve their application. Attention should be paid to
lighters, barges, and other craft on our rivers and canals.

Wooden stagings and platforms frequently harbour immense
numbers of rats; they should be replaced whenever possible by
solid structures of brick and concrete.

* All hawsers should be furnished with rat-shields, such as circular discs
of metal not less than 4 feet in diameter.

30 Rats and Mice

With regard to the Destruction of rats in towns :—

Trapping should be done continuously and systematically at
all rat-infested places; and wherever possible they should be
attacked with cats, dogs and ferrets.

In badly infested areas public rat-catchers should be
appointed. The position of these men when appointed should not
depend upon whether rats remain to be caught or not; if the rat-
catcher succeeds in cleansing a badly infested locality his pay
should be increased, and it should remain at the higher level for
so long as he succeeds in keeping the place free from rats.*

In normal times, when many persons are unemployed, the
payment of small premiums for each rat caught has good results.
This method has, of course, been tried on many occasions in this
country from the eighteenth century onwards; its failure here
hitherto is partly to be ascribed to the fact that the premium
offered was often too beggarly to attract, but chiefly to the fact
that such a system was only tried in certain districts and never
throughout the country as a whole at any one time. Zuschlag
was the first to put such a system upon a scientific basis; after
much experiment and agitation his scheme was embodied in the
Danish Rat Law, and it worked with good results in Denmark
and in other Scandinavian countries. The premium to be paid
should be settled independently in each district; its amount must
depend upon the state of the labour market and the scale of wages
for unskilled labour in each locality. If too low the premium
attracts children only; if too high it tempts fraudulent persons to
try their cunning. In ordinary times this system is calculated to
enlist the services of a large amount of nondescript or casual
labour. In Denmark the rats were received at the fire stations ;
the tails of the rats brought in were cut off by the firemen,f and
the latter used them as their vouchers for the money they had
paid out as premiums. In certain German towns the system did
not work so well; the premium offered was too low, and, what
was still worse, the rats were received at the police stations. Those
who might have been attracted even by such small rewards did
not care to run the risk of visiting the police, for as Zuschlag

* Proper supervision of such men is, of course, pre-supposed.

+ In the interests of the public health it is essential that the whole rat
should be surrendered—not merely heads or tails. Without such a stipulation
the carcases may become more dangerous than the living animals.

et

as Enemies of Mankind. 31

says: ‘Quand on est sans pain et sans travail, la conscience n’est
quelquefois pas tranquille.”’

In all towns occupiers of rat-infested property should be
obliged to notify the local authority of the fact that their premises
are infested with rats. For the purposes of certain trades—e.g.,
the catering trade—the use of rat-infested premises should be
forbidden. Some years ago the writer had much personal experi-
ence of two rat-infested eating-houses situated in a main street of
the City of London. These were next door to each other; the
one, more expensive, catering for professional men, was in a
comparatively modern building; the other, a cheaper place, was
in a house dating from the seventeenth century. Rats swarmed
in both of them, doing great havoc to the stores. Hach restaurant
blamed the neighbouring establishment for its rats, and each had
an extensive underground kitchen. Food was frequently con-
taminated ; rat dejecta not unfrequently appeared in portions of
vegetables, jam, or stewed fruit; and rat fleas were by no means
uncommon in cornflour blancmanges and suet puddings. In the
evening hordes of rats came up into the public rooms from below,
as the shops were closing. On one occasion workmen, who had
been painting the walls of one of the establishments during the
night, informed the writer that the rats had been so numerous
upon the floor that the men were afraid to descend from their
trestles. Dogs were kept in both premises, and on ordinary nights
had the run of the shops; these killed many rats each night, and

entrails of their victims were sometimes tossed by the dogs into

the urns on the counter. Despite the rats, the writer, being a
chess player, remained a customer at one of these shops until a
new building was erected across the road; that building was of
the rat-proof type and its ground floor and basement became a
restaurant. It has been so used for some ten or fifteen years
now, and it has remained free from rats, although these pests are
quite common in adjoining and older houses. In our opinion no
refreshment licence should be granted in respect of any premises
not certified to be free from rats and to be rat-proof.

Rats, of course, cannot be attacked with equal success at all
places in towns. Sewers are usually infested, and it is naturally
difficult to cleanse them of rats. In those of Paris a means of
electrocuting them has been introduced; a live wire is supported
at a height of a few inches, and dainties are hung at intervals
above it. When a rat attempts to snatch a morsel it puts its paw

32 Rats and Mice

upon the wire, and its existence is suddenly terminated. Boelter
states that the London sewers in the neighbourhood of Soho
are now free from rats because of the quantities of petrol which
find their way into the drains from the motor works of that
locality.

Besides petrol, the following substances can be introduced .
into burrows and runs to induce rats to exchange secure
quarters for those in which they can be more readily attacked :—
Gas tar, chloride of lime, caustic potash, strong solutions of
ferrous sulphate ; thin whitewash may be poured into burrows ;
and freshly-slaked lime placed dry in the burrows or runs is
effective.

In the Country, preventive measures of the kind suggested
above for towns should be adopted whenever and wherever an
opportunity presents itself. Stacks should always be made rat-
proof where possible; this may be done by building them upon a
platform supported on piles ; the platform should be raised at least
3 feet from the ground, and the piles should be furnished with
metal rat-guards of at least 4 feet in diameter. Efforts should be
made to render farm-buildings, stables, cow-houses, barns,
slaughter-houses, mills, and rural railway stations rat-proof ; and
great attention should always be paid to the necessity of keeping
the food supplies of domestic animals from contact with rats.
Preventive measures are naturally far more difficult in the country
than in the towns; nevertheless, they are important, and where-
ever they can be adopted they will amply repay the expense and
trouble involved.

On the other hand, destruction of rats is comparatively
simple in the rural districts and far less costly; for instance, each
rat taken by one London body costs on an average ls. 8d., while
in Haddingtonshire the average cost was only 3?d.; but as
pointed out above, the destruction must be general and carried
out with the approval and co-operation of all. Well-organised
rat clubs or the payment of well-chosen premiums will no doubt
do great good in securing the services of the younger and the
poorer inhabitants. But every landowner and farmer should
recognize that it is his duty, in his own interests no less than in
those of the community, to kill the rats and destroy their breeding
haunts on his property or holding; that if he fails in this duty
he simply negatives the results obtained by his more enlightened
neighbours.

as Linemies of Mankind. a2

The fullest protection should be accorded to all Stoats,*
Weasels, Owls, and Kestrels. They are most valuable allies
and destroy large numbers of rats. It is not a sound argument
to object, as some do, that a weasel will not attack a full-grown
rat; weasels do a better service than that—they kill large numbers
of young rats, and young rats are far more numerous than old
ones, and potentially far more dangerous. If these beasts and
birds of prey occasionally help themselves to a young game bird
or a rabbit it is not of much consequence; the rats they have
destroyed and will destroy, if unmolested, would have done and
will do, if not destroyed, far more damage of that kind. In fact,
many of the crimes laid at carnivorous doors are crimes committed
by the rat.

Poisoning should be done once or twice a year—in the spring
and in the late autumn. March is said to be the best month for
this, because food is short and the rats will take the poisoned baits
readily. Arsenic is recommended by one very experienced rat-
catcher as the best and safest poison, because in the small doses
necessary to kill rats it entails little risk to domestic animals; if
they find and eat the body of a rat so poisoned the small quantity
of arsenic in the body is said to act upon them merely as a
purgative. On the other hand, the United States Public Health
Service is convinced, according to Lantz, “‘ that arsenic is a very un-
reliable rat poison.’’ Barium carbonate is a very good and probably
the safest poison; it has the merit of being tasteless and odourless
when conveyed in a proper medium. A proprietary article—
“Sanford’s Poison’t—has recently been highly praised by
Mr. Sharpe, in the Field. Strychnine and phosphorus are also
used effectively ; but they are most dangerous, and must be used
with the greatest caution.

Poisoned baits should always be placed well within the burrows
and out of the reach of other animals; by this means also the risk
of a rat carrying a bait off and leaving it in an exposed place is
diminished. Where desirable to poison rats on a feeding ground
away from their burrows, as in a barn, it is necessary to convey

* This recommendation to protect Stoats and Weasels does not, and will
not, meet with the approval of all; in the writer’s opinion it is one of the
most important measures, not only against Rats but against Mice and Voles
(see pp. 43-47).

t Dr. Manby informs us that phosphorus is the poisonous ingredient in
** Sanford.”’

oa. Rats and Mice

the poison in loose materials (like meal) which cannot be carried
away, and also to prevent other animals from gaining access to
the poisoned food. Rats commonly become thirsty after poisoning,
and make their way to water; it is, therefore, very necessary to
safeguard wells, etc., before commencing poisoning operations,
otherwise bodies of rats fall in, and their decomposition may have
serious consequences for the consumers of the water.

Outdoor rats can be poisoned in their burrows by means of
gases—-such as carbon bisulphide, sulphur dioxide, or chlorine.
Carbon bisulphide is the most convenient one to use out of doors,
but being very inflammable it requires great care in handling. A
piece of tow, cotton-wool or other absorbent material is saturated
with the liquid and pushed into the burrow as far as possible; the
mouth of the burrow is then tightly closed with earth. Although
fumigation (preferably with sulphur dioxide) is most useful on
ships, it is not so effective in buildings owing to the difficulty of
confining the gas used; and if effective indoors, the decomposition
of the dead rats in their inaccessible hiding-places is apt to entail
unpleasant consequences. After poisoning or fumigation the
burrows should always be run with gas-tar.

In low-lying districts burrows may sometimes be flooded with
good effect; many full-grown rats perish by drowning, and, what
is more important, many litters of young can be thus destroyed.

Virus of one sort or another is occasionally effective. Such
bacteriological preparations are, however, costly, and they require
considerable skill in their use. Their virulence varies, and dis-
appears more or less rapidly on exposure to light and air. The
disease communicated usually propagates itself from rat to rat
very slowly ; and, what is worse, less than fatal doses render rats
immune. The harmlessness claimed for all towards animals other
than rats and mice is, at least in many cases, open to question.
Although bacteriology may furnish us any day with an efficient
means of destroying rats at will, it cannot be said to have done so
yet. Not one of the many preparations sold can be recommended
as a safe and thoroughly reliable means of destruction.

Trapping should be done at all times continuously and system-
atically, and special attention should always be paid to water-
courses and drains. Steel spring traps are the best for general
use, and when used out of doors they should be set early in the
day; they should be regularly visited at dusk, late at night, and
early in the morning. Various baits may be used. The trap

rs >
4

as Enemies of Mankind. 35
should be handled as little as possible in setting, and the hands
should be well rubbed with earth before touching it. Rats can
often be taken in their runs by means of unbaited traps. It is
often useful to bury the traps under a thin covering of earth, chaff,
or other loose materials lightly sprinkled over them with a sieve.
Many useful hints on trapping may be found in the papers
recently published in the Meld by Mr. Sharpe (January to March,
1918).

In some cases, as where a run passes along a wet ditch, or
where the rats show themselves to be very shy, rats can be readily
caught by traps set and covered by a thin stratum of water; traps
so covered are not betrayed by their odour. Where traps thus set
are baited, as when used indoors, the bait hangs just above the
surface of the water. A method of this sort has been described
by an American writer (10), and more recently (and quite in-
dependently) by Mr. Sharpe in the fveld. Mr. Sharpe supports
the trap on three nails in a gap cut in a wooden platform, which
is placed just under the surface of the water in a tank or ina
hollow dug in the bed of a ditch. When the trap is sprung it is
‘thrown off the supporting nails and sinks with the trapped rat
down into the tank or hollow beneath.

In barns, granaries, and other places large numbers of rats
can be caught alive by box-traps or strong wire cage-traps, if these
are properly baited and concealed. Pitfalls also, such as large
vessels sunk in the ground, or barrels with pivoted lids, are often very
effective when properly baited; in these traps a decoy rat may be
placed with advantage; a female immediately after she has given
birth to a litter makes the best decoy imaginable. A very neat
and inexpensive contrivance, the invention of two poor Swedes, is
described by Zuschlag. A wooden stockade about 3 feet 6 inches
high is erected so as to enclose a triangular space, of which each
side is about 12 feet in length. In one of the sides is a gap
18 inches to 2 feet wide ; this gap is closed at will by means of a
heavy slide held up, when the trap is open, by a cord and pulley.
In the base of the side opposite to the gap is fitted a funnel, of
wide enough bore to admit of the passage of a rat; the funnel
opens into a sack placed behind the stockade. The inner
side of the stockade is smooth, so as to give as little foothold as
possible to rats attempting to climb out; and old iron plates or
tiles are placed so as to overhang the edge of the stockade, inclined
at a suitable angle to prevent the rats from leaping out. The trap

36 — Rats and Mice

is baited with any attractive stuff, such as old bones or a dead dog;
the slide is opened and the rats are allowed to regale themselves
freely for a time. Later the man who is to work the trap secretes
himself; when he judges that enough rats have entered the en-
closure hereleases the cord controlling the sliding door. The operator
and his comrades then hurry to the trap and scare the rats by
beating its sides; the rats, unable to climb or jump out, soon
discover the funnel and pass through it into the sack. When the
sack is full a board is dropped over the mouth of the funnel, and
the men beat the sack with shovels until all the rats within are
killed. With this trap the inventors caught upwards of 5,000 rats
in a very short space of time. In trapping, however, far less
depends upon the trap than upon the trapper ; the good man will
take rats with the most primitive contrivances if put to it; the
unskilful man will be unable to use the best.

Large numbers of rats can be killed by means of men and dogs
towards the close of reaping, mowing, and threshing operations, if
care has been taken to prevent the escape of the rats. In the case
of cornstacks this can easily be done by surrounding them with a
temporary fencing of rat-proof wire-netting placed at a distance,
sufficient to prevent the rats jumping over it from the stack.

Many rats can also be killed in their runs and elsewhere at
night by the flash-light method; thus they frequently come to the
outer surface of ricks at night. If a strong light be suddenly
flashed upon them, the rats are temporarily dazed, and they can be
whipped off to the ground, for dogs to deal with, by a man armed
with a long stick.

Ii a general campaign against rats should be organized
throughout Britain, it should proceed on some such lines as the
following. The country should be divided into districts, each
having as far as possible water for its boundaries. Work in each
district should commence at the boundaries and proceed gradually
towards the centre; the more the work is supplemented by
individual effort the more effective it will be; and the full co-
operation of all landowners and farmers will be essential.
Systematic operations (poisoning, fumigation of burrows, etc.)
should commence immediately after the harvest, and they should
be continued into the spring, the ground being traversed more
than once if possible. Trapping, of course, should be done
throughout the year. With regard to labour, a correspondent
states that it takes one man to every 2,000 acres to conduct

j
A
4
a

as Enemies of Mankind. 37

trapping operations properly ; on this estimate between 20,000 and
30,000 men would be required for such work in Britain. But if
the work were properly organized, and one could count on the co-
operation of all sections of the community, far fewer men should
suffice. Thus, in East Haddingtonshire three rat-killers were
employed throughout the year; each man was allotted a district
of from twenty-five to thirty farms, and lived in the centre; each
worked gradually from the boundary of his district towards his
home. While the best trappers are usually retired gamekeepers,
any man of ordinary intelligence can become proficient with a
little training. It is suggested that rat-catching offers a good field
of employment for many disabled soldiers and sailors.

In a general campaign of the kind suggested, the men engaged
must be paid by settled wages and not by premiums on the
numbers of rats caught. If one pays so much a rat, the rat-
catcher will leave a farm as soon as rats become scarce, and before
he has finished his work, for another which promises a bigger bag.
In a short time the condition on the first farm will be as bad as
before.

2. HOUSE MICE. Genus MUS.

Only one species of this genus inhabits Great Britain :—

Mus musculus. The Common House Mouss (Fig. 1).
Size small ; general form slender—like a Black Rat in miniature.

‘ eo

Fic. 1.—Hovusr Mouse (Mus musculus).
(Natural Size.)

38 Rats and Mice

Ears moderately large, covering the eyes when pressed for-
ward, clothed almost everywhere with short fine hairs.

Tail about as long as the combined length of the head and
body; frequently longer, rarely shorter.

Feet short and broad. In the hind-foot a small supplementary
pad is present on each side near the lateral margins of the pads at
the bases of the innermost and outermost toes.

Fur soft, intermixed with grooved bristles as in the rats, but
these bristles are too slender to affect sensibly the quality of
the coat.

Teats: females with ten mammae, three pairs on the chest,
two pairs towards the groin.

Colour variable.

Indoor specimens are usually dusky grey above, more or less
darkened by slate or black along the middle of the back, and
gradually paling on the sides to the ashy grey of the underparts ;
ears brownish; feet dusky above, not contrasting with back; tail
dull brown, occasionally lighter below than above.

Outdoor specimens have the hair-tips often more or less ex-
tensively bleached to a yellowish brown; so that such specimens
usually appear more or less sandy or tawny in colour.

Albino and melanistic specimens are not uncommon. In
domestication numerous varieties of colour and pattern have been
produced as fancy breeds.

Weight of adults normally about 16 grammes, or slightly over
4 ounce.

Measurements in millimetres :—

Hind-foot,
Head and Body. Tail. without claws. Ear, from base.
70 to 100 70 to 102 17 to 19°4 11 to 16

In its outdoor dress this animal may sometimes be confused
with the Long-tailed Field Mouse; its shorter, broader, and
dusky feet, and smaller and less protruding eyes are diagnostic.
The skull and teeth (Figs. 5 and 6, pp. 57-59) are so peculiar that
they cannot be confused with those of any other British species.

History.—Like the rats, the House Mouse appears to be of
Asiatic origin. Its arrival in Europe dates, however, from a very
remote period. It was well known to the ancient Greek and
Roman writers, and it figures in our own records and literature
for more than one thousand years. On certain islands, such as
St. Kilda and the Faerées, it has existed long enough to develop

as E:nemtes of Mankind. 39

local races, sufficiently different from their parent race to be
regarded by many naturalists as distinct species. Over much of
continental Europe, particularly in the warm Mediterranean
region, a somewhat smaller form is found living a perfectly wild
life far from houses; this outdoor mouse is called M. spicilegus,
and Miller and others regard it as perfectly indigenous.

At various times remains of the House Mouse have been
recorded as fossils from British Pleistocene deposits, but the
writer, well acquainted with this branch of the subject, thinks
that no satisfactory evidence of the presence of this species in
Pleistocene Europe has as yet been found. In his view, the
House Mouse probably came to Europe from Asia with a people
not older than the Neolithic, and then spread all over Europe,
including the islands. While it continued to infest the habitations
of man in all places, individuals found that they could in certain
localities live quite well out of doors; these, therefore, resumed a
wild habitat, and their descendants have developed into the peculiar
local or wild races mentioned above. All mice are plastic animals,
and the House Mouse is no exception to the rule. To-day, in
America, where no Muwrinae are naturally present, the House
Mouse is living in the fields as well as in the houses, and it is
developing local races or sub-species; indeed, in South America
it is tending to lose its posterior molars, and if those teeth were
constantly absent, and we were ignorant of its history, the South
American animal would be classed by many zoologists as belonging
to another genus.

General Habits.—The general habits of the House Mouse
resemble those of the Black Rat. It is a good climber and jumper ;
it swims well, but rarely takes to water voluntarily. Its senses,
with the possible exception of sight, are acute. Like rats, it shows
a propensity for following a beaten track, and of this advantage
can be taken when trapping is being done. Its nest of soft
materials is placed in any convenient recess—in walls, behind
skirtings, under floors or steps, in bookcases or other articles of
furniture, and in many other places.

Its food comprises every description of human food, and even
tobacco; grain of all sorts and seeds of many descriptions are
readily eaten.

Breeding ‘Habits.— House Mice are very prolific; they
attain sexual maturity when three months old. The sexual season
D

40 Rats and Mice

of the females is a very long one. The period of gestation is
normally from nineteen to twenty-one days; it may in certain
circumstances be shortened to twelve or thirteen days. ‘ Heat,”’
not lasting longer than twelve hours, rapidly succeeds parturition.
Many litters are born throughout the year, but fewer in the cold
months. The number of young per litter is between five and six,
but it may be as many as nine or as few as two. The young are
born blind, naked, and pink; they grow rapidly, and are able to
leave the mother in less than three weeks.

Economic Importance and Relation to Public Health.
—Few houses in Britain are permanently free from House Mice.
When the number present is small they do comparatively little
harm, and many people rather welcome the occasional and sudden
appearance of the little beast on their hearths. But when a large
colony is present it is quite a different matter. The mice become
then an intolerable nuisance, eating large quantities of our food,
spoiling far more with their droppings, and tainting every place
and thing with which they come in contact with their strong and
unsavoury odour. Birdcages are robbed of their seed; linen,
clothing of all kinds, and books are attacked, and holes are
gnawed in the woodwork in all directions. Traps and cats are
now brought in to fight the pests; the members of the household
grow more careful in securing the food supplies and in placing
other things beyond the reach of the mice; in a short time, as a
rule, the premises revert to their normal condition. The loss
occasioned by such a visitation is often quite considerable.

In shops, warehouses and granaries, and on farms House Mice
are normally more abundant; in such places they often do great
damage and cause much loss. In the materials stored they find
abundant food and shelter, and accordingly they breed at an
amazing rate.

Most countries are visited periodically by “‘ mouse plagues.”
These plagues usually develop in summers following mild winters
and previous seasons of great plenty. Such favourable conditions
of climate and nutrition favour the mice by decreasing the normal
natural mortality, and by increasing the size and the frequency of
the litters born. Usually all the species of Muridae inhabiting the
district affected contribute to the formation of the ‘‘ mouse plague.”
Thus in Britain what are called ‘vole plagues” are marked not
merely by a great increase in the number of voles present, but

as Enemies of Mankind. Al

great hordes of Field Mice and outdoor-living House Mice are
developed simultaneously. Such a plague brings ruin and devas-
tation to the countryside; the ground is riddled with holes, the
crops and many young trees utterly destroyed. The plague may
yun a course of several months, but sooner or later disease
breaks out among the rodents, they succumb in millions, and in a
short time their numbers are once more normal, or sub-normal,
and the plague is at an end.

Recently South Australia and Victoria have been visited by a
very severe ‘mouse plague,’ the worst ever experienced in
Australia. The principal species involved was the House Mouse,
but it was assisted not only by various native species but by
battalions of rats as well. The plague developed in the bush as
_ well as in the wheatland in 1916 and 1917, after two abnormally
heavy harvests. The wheat grown was sold to the British
Government, and the grain was stacked in bags ready for ship-
ment. Shipping was cut off and the stacks remained unprotected
from a possible attack by the rodents. As cold weather approached
the mice invaded the stacks ; an eye-witness of the result says :—
“The wheat stacks instead of being as orderly as a brick wall are
now evil-smelling heaps of wheat, mice alive, mice dead, and
rotten bags.” The damage done to the wheat is estimated to be
well over £1,000,000; what is worse, much of that which has
been re-bagged is in an indescribably filthy condition. The mice
were in billions. One farmer put down poisoned meat in his house,
and next morning he picked up 28,000 dead on his verandah, and
he added that he only stopped then ‘‘ because he was tired.” At
one wheat-yard 70,000 were killed in an afternoon; these must
have weighed about one ton. Myriads died from a disease, in
appearance somewhat resembling ulcerative syphilis; and the
men trying to cleanse the stacks contracted a kind of ringworm.
Large quantities of hay were also ruined, and horses fed upon the
dirty residue were killed. Of course, much other property was
injured ; thus, in a grocer’s shop at Port Lorne, South Australia,
many packages of lead pencils were devoured—the flavour of the
wood appealing to the mice; and they ate the leaden bullets out
of some hundreds of cartridges. Here also the seaweed on the
beach was swarming with mice.

As regards their general relation to the public health, many of
the remarks made above as to rats will apply to mice equally
well: In certain circumstances they convey plague, and there is

D 2

A2 Rats and Mice

no doubt that they help in perpetuating trichinosis among swine.
Mice, when present in such numbers as in the Australian plague
just discussed, with their parasites and diseases, must constitute
a grave danger. Quite apart from the risk of disease being
conveyed by the living mice, there is a serious peril of water
becoming contaminated by their putrefying bodies. The use of
grain fouled by them, for human food or even for that of domestic
animals, is an extremely risky proceeding—unless, indeed, really
efficient means of cleansing and sterilizing it can be devised.

Control of the Mouse Population.—Should we succeed in
exterminating or greatly reducing the rat population of this
country, we shall in all probability disturb the balance of Nature
still further in favour of the House Mouse and our other small
Muridae. The presence and competition of rats greatly diminish
both the food-supply and the space available for mice ; remove the
rats, and there will be nothing to hinder the steady natural increase
in the numbers of mice until the latter have filled up the vacancy
left by the rats. If, therefore, we fail to adopt appropriate
measures against mice at an early stage in our campaign against
rats, we shall find ourselves confronted, in due and rapid course,
with a mouse plague.

The steps to be taken against mice are similar to those re-
commended against rats. The chief of them are the following :—

1. Protection of food supplies.
All food, whether of man or beast, should be kept, as far as
possible, in mouse-proof receptacles.

Unprotected accumulations of edible refuse should never be
permitted.

2. Diminution of the available shelter for mice.

Rubbish heaps of all sorts should be abolished.

Effective rat-proofing of buildings will render them mouse-
proof to a considerable degree.

Mouse-holes should be stopped wherever possible; for this

purpose many expedients, such as filling with cement and broken
glass, or running with gas-tar, are available.

3. Destruction of mice.

Indoors and about houses this is best accomplished by means

+ 20 or Sait pee ieee AIR

as Enemies of Mankind. 43

of cats and traps. Mice are not, as a rule, suspicious of traps ;
almost any trap and any bait will take a mouse. In places where
there is an abundance of attractive food it is usually well to bait
the traps with a delicacy rare in the locality; for instance, cheese
may be a good bait in a fishmonger’s shop, while fish might be
irresistible to the mice of the cheesemonger.

4. Protection of the natural enemies of mice.

Many birds and beasts prey upon mice. The most important
in this respect are owls, of all species, and weasels; these creatures
should be most carefully protected. It should be recognized by all
interested in agriculture that they have no better and no stronger
friends than these. Everybody on the countryside, from the squire
to the schoolboy, should be taught to look upon the wanton
destruction of an owl or a weasel as one of the blackest crimes
possible amid rural surroundings.

3. THE BALANCE OF NATURE AND THE
PROTECTION OF CARNIVORA.

During the passage of this work through the press, the recom-
mendation that Stoats and Weasels should be fully protected
(p. 33) has met with some adverse criticism. In making that
recommendation the writer is fully acquainted with the views
commonly held by gamekeepers ;* and he is perfectly well aware
that the majority of them will disagree with him.

The recommendation may be supported by an appeal to first
principles, so well known that to many it will seem unnecessary
to recite them here; the necessity to recall them arises from the
fact that apparently they are forgotten sometimes, when dealing
with questions of this kind. Besides, a short statement as to what
is meant by the “ Balance of Nature” may not be unwelcome to
the reader without technical knowledge.

If any organism were allowed to increase at its natural rate of
multiplication unchecked it would speedily fill the whole surface
of the globe to the exclusion of all other beings. Hach species is
kept in check primarily by having to compete for space with all
other species; apart from innumerable other factors, this alone is

* For recent expressions of such views, vide correspondence in The Game-
keeper, December, 1917, February and May, 1918; also GUNTHER, pp. 53
and 63. .

A4 Rats and Mice

sufficient to control the numerical representation and distribution
of plants. All animals derive their sustenance from plants, either
directly or indirectly, or in both ways.

Hach country has its own geological and geographical history,
as well as its own climatic conditions; further, climate and soil
vary with the district. On all these things the nature of the
vegetation depends; they determine chiefly what species of plants
may occur, and which of these will thrive. These things, and the
plant-life they control, determine further what animals may live,
and which of these will prosper in a given locality. All species, be
they animal or vegetable, are doing their utmost to feed, grow, and
reproduce their kind. The result of all these conditions and forces
is that each individual or species reacts, to a greater or lesser
degree, upon all other individuals or species brought directly or
indirectly in relation with it; its existence and activities may
favour, may hinder, or may both favour and hinder the existence
and activities of other organisms. In this way plants and animals,
and the individual species of each kingdom, are everywhere so
closely adjusted to each other that they might be likened to the
cells of the honey-comb of the hive-bee; but whereas in the honey-
comb we find space filled with a number of similar simple
geometrical forms of one magnitude, in the case of organic nature
we must imagine space to be filled with an enormous number of
figures of diverse form and size. No element can be added to or
taken away from such a complex without causing a more or less
far-reaching disturbance of the whole. There may be thousands
of links in the chain of cause and effect necessary to determine
which of two species of mouse, for example, shall predominate in
a given locality; so far as human intelligence is concerned the
complexity of that chain is infinite.

Every district normally contains the full number of small
mammals and birds it is capable of supporting ; what that number
is depends upon what species are present and the relative propor-
tions in which they occur; these factors in turn depend upon the
conditions named above. But many small mammals and small
birds are characterized by a high fecundity; and in each year
each of such species produces far greater numbers of young than
are necessary to maintain the normal stock; if over-population,
with all its attendant evils, is not to ensue, the surplus must be
removed—and in normal conditions it is-removed. The chief
destructive agents are ACCIDENTS, such as misadventure, sickness,

etal

% PAREN UI te ae EER PMN Sittcdtyy ae EY i ee yo act 2

+ ROSY

as Enemies of Mankind. 45

or the attacks of enemies (e.g., carnivora and parasites), the effects
of COMPETITION and overcrowding, and, above all, the WEATHER,
with its great powers of inflicting injury upon any species, either
directly or indirectly (as by curtailing the food-supply). These
Operate, singly or in combination, at all times on individuals of all

ages; accidents and competition press most hardly, perhaps, upon

embryos and young; the weather destroys chiefly in winter and
spring.

The precise mode in which the surplus is removed varies with
the species. Despite the heavy toll levied by accident and com-
petition, free-living creatures, like small birds, usually have a
large surplus at the end of summer; and that surplus must be
removed by the severe weather of the following seasons. On the
other hand, more or less earth-bound animals, like the Muridae,
with their habits of constructing warm nests in dry burrows and
of amassing stores of provisions, are enabled to withstand all but
the most severe weather. In their case the surplus must be
removed chiefly by accidents and competition. Their habits render
small rodents the easiest of prey ; in fact, they form the staple food
of every one of our carnivorous mammals, with the exception of
the Otter. Foremost among rat- and mouse-killing mammals are
the Stoat and the Weasel; working incessantly, they kill far more
than they devour; many mature and healthy rodents fall to them,
but the young just leaving the nest, with such adults as are weak
and sickly, form the great majority of their victims. Among British
birds the Barn Owl, Short-Eared Owl, Long-Hared Owl, Tawny
Owl, Common and Rough-Legged Buzzards, Kestrel, Rook, Carrion
and Hooded Crows, Raven, Magpie, Heron, and some Gulls may
be enumerated as more or less important rat- or mouse-killers ;
indeed, in this respect the importance of the Owls and Kestrel
can hardly be over-estimated. The stronger and more efficient
the carnivora (including in that term all the animals which
habitually or occasionally prey upon rats and mice), the more
completely and automatically will the surplus rodent population
be removed as it arises.

In a well-balanced or natural fauna, carnivora will never
extirpate the species upon which they feed; the prey is secured
only by work; and physiologically it costs more than it is worth
to secure the prey when it becomes scarce. Herein lies the chief
natural check upon the numbers of carnivorous animals; in addition,
carnivorous species prey upon each other when opportunity offers.

46 Rats and Mace

It is true that a Fox, if not prevented, will quickly kill every bird
in a pheasantry or hen-roost to which it gains access; but this
does not affect the principle-—pheasants and hens do not enjoy, in
this country, the natural protection they require; in their own
homes, as wild birds, they are beset with foes, but nevertheless
the stock survives.

The high fecundity of small rodents has been developed
apparently to enable them to survive the many attacks to which
they are exposed; in purely natural conditions and in average
seasons it is probably not excessive for that purpose. The precise
rate of breeding, however, is dependent upon the food-supply and
the meteorological conditions to a very large extent. When both
are favourable to the rodents, they multiply at an amazing rate,
and the carnivora (of all kinds), even when abundant, may be unable
to remove so large a proportion as usual of the surplus produced.
If the ensuing winter and spring be mild, part of the surplus will
remain over to the following breeding season; and should one or
two years of this character succeed each other the inevitable
result will be a ‘“‘Mouse Plague.” The development of such a
plague involves necessarily great monetary loss to the rural
community, and at moments such as these it might lead to
national disaster. The plague cures itself in due course by
starvation and disease among the rodents, but the cure may bring
with it a deadly threat to human health. The risk of Mouse
Plague developing is continuous; by carefully preserving our
carnivora (Mammals and Birds) in due numbers we minimize the
risk and ameliorate the evil whena plague happens. The weather
may be lenient to rodents, the carnivora never.

Enough has now been said, perhaps, to justify the assertion
that carnivora in general, and Stoats and Weasels in particular,
are among the best friends the British farmer and the public at
large possess. But a special word has to be addressed to the
game-preserver pure and simple. He must not forget that a
carnivorous palate is not the exclusive property.of carnivorous
animals properly so called; the development of such tastes is
merely a matter of opportunity and competition; squirrels, for
instance, are carnivorous whenever and wherever they get the
chance. The Brown Rat is on occasion almost as bloodthirsty as
the Stoat ; if Stoats and Weasels were exterminated, the numbers of
this species would increase very rapidly; as a consequence large
numbers of them would be obliged to assume the carnivorous réle

— 9a ora

‘
f
i.

as Enemies of Mankind. 47

of their banished foes; in such a case their high fecundity would
make them most formidable; game and poultry would suffer
immediately, and to a far greater extent than they have ever done
from all our living carnivora combined.

It is open to question whether entire immunity from attack by
carnivora is a good thing, in the long run, for game. Be that as it
may, the preservation of a sufficient stock of carnivora is of vital
importance to the welfare of general agriculture and the national
interest. If the continued existence of predatory animals be really
incompatible with game preservation—so much the worse for the
latter.

With all the foregoing considerations in mind, it may be safely
asserted that not one of our living native species of mammal or
bird should be persecuted to extinction; each has to play its part
in maintaining the balance of nature in this realm ; and the present
state of knowledge does not warrant a belief that any member of
the native fauna may be safely dispensed with. It may be
necessary to check the undue increase of certain species from time
to time, to set bounds to their wanderings, and to protect our
possessions from their ravages; but that is all. The projected
extermination of the Brown Rat, Black Rat, and House Mouse, in
Britain, is justifiable biologically solely upon the ground that these
three species are alien; but just because they are now so well
established here, the extermination of the Rats, without due pre-
cautions, may lead to serious trouble with other species, as
suggested at p. 42. As a parting word to the agriculturist it may
be said that the less he persecutes the wild fauna, the better off he
himself will be in the long run. Everything worth having costs
something, and a wild fauna is no exception to that rule. A reason-
able burden must be borne on account of each species involved ;
if that burden be refused we may have to shoulder a heavier one.

I would take this opportunity of confessing my great in-
debtedness to the little book by the late O. Winge, cited below ;
first published in 1886, a second edition appeared in 1911,
furnished with a preface and notes by the author’s brother Dr.
Herluf Winge, the great naturalist of Copenhagen. If this book
were translated it might be read with profit—though not always
with pleasure—by all interested in the welfare of Rural Britain, and
particularly by those who doubt the value of carnivora, or who think,
for example, that the destruction of such ‘“ vermin” would lead to
a great increase in the numbers of ‘‘ useful” insectivorous birds.

48 Rats and Mice

4. NOTES ON STRUCTURE AND CLASSIFICA-
TION OF THE MURIDAE, WITH A KEY TO
BRITISH SPECIES.

In these islands everybody is familiar with the general appear-
ance of a rat or a mouse; and this familiarity has often resulted
in the names ‘‘rat” and “mouse” being applied, in consequence
of superficial resemblance, to animals which in structure are very
different from true rats and mice. Properly these names can only
be given to mammals of the order Rodentia; and then not to all
rodents, but only to such species—and there are many hundreds
of them—as belong to the family Muridae. We thus learn that
in dealing with the rat-like and mouse-like creatures of the world
it is not sufficient merely to note their differences or agreements
in colour and general external form; in order to determine their
true zoological position we must examine their anatomy in greater
or less detail, paying particular attention to the structure of their
skulls and teeth—since these organs furnish highly important
characters.

In all Muridae the clavicle or collar-bone is well developed,
and the tibia and fibula, the two bones of the lower part of the
leg, are, to a great extent, fused together. In most genera the
thumb is rudimentary. In the skull (Fig. 2) each frontal bone
lacks a postorbital process; each zygomatic arch is formed
chiefly by the zygomatic process of the maxillary and squamosal
bones, the jugal being reduced to a mere splint between the two
and not articulating with the lachrymal bone in front; the lower
root of the maxillary zygomatic process is flattened into a large
more or less vertical plate of bone, which forms the outer wall of
the infraorbital canal and gives attachment to that part of the
great masseter or cheek-muscle, which is chiefly concerned in
pulling the lower jaw forwards in the important work of gnawing.
The infraorbital canal is large and shaped like a comma; its
lower and narrower part transmits the sensory facial nerve and
vessels, while its upper and wider portion lodges a slip of the
masseter muscle. There are never more than sixteen teeth. As
in all other rodents (excluding the hares and their allies), four of
these teeth are incisors and are placed, one on each side above
and below, in the anterior ends of the jaws. These teeth (Fig. 2 D),
as the instruments by which the characteristic gnawing function

as Enemies of Mankind. AQ

is performed, are highly modified. Tach has a thick plate of hard
enamel on its anterior surface, but the relatively soft dentine is
exposed for a greater or less width on the posterior side; conse-

Fig. 2.—Fretp Voue (Microtus agrestis), skull enlarged.

A. Dorsal, B. ventral, C. lateral views; p.m. premaxilla, m. maxilla,
j. jugal, s. squamosal, p. parietal, ¢.7. left temporal ridge ; arrows in A.
and C. pass through infraorbital canal; dotted lines in C. indicate
course of upper incisor. D. right ramus of lower jaw dissected, 7. the
incisor, a. its anterior enamel, p.c. its pulp-cavity, c.t. the rootless molars.

quently with wear the tooth develops and maintains a chisel-like
cutting edge. The shaft of each upper incisor forms a large
segment of a small circle and passes back through the premaxilla
into the maxilla, where it terminates near the anterior molar;

50 Rats and Mice

that of each lower incisor forms a smaller segment of a much
larger circle and proceeds backwards beneath, or beside, the roots
of the cheek-teeth, to terminate in the ascending portion of the
mandibular ramus, behind and to a greater or less extent above
the level of the molars. The base of each incisor is hollow and
open; in life the cavity lodges the dentinal pulp from which the
tooth is developed; growth is continued throughout life and the
tooth is gradually pushed forwards. Under normal conditions, in
adults, the growth and forward movement of the incisors take
place at a rate which exactly compensates the loss by wear
suffered at the working end. Separated from the incisors by a
long toothless interval, or diasteme, are the cheek-teeth; of these
there are never more than three on each side above and below,
and the anterior one in each jaw is always considerably larger
than those behind it. In many forms the posterior tooth is greatly
reduced, and in some it is normally absent. The great relative
size of the front cheek-teeth is probably due to their position in
the jaws, for they are placed just at that point where the com-
bined activities of the temporal and masseter muscles produce the
greatest pressure between the upper and lower tooth-rows.

Now the characters described above, with others too numerous
to discuss here, are shared by all Muridae; any animal showing
such a combination of characters would be entitled to a place in
this family; and it would in ordinary language be described,
according to its size, either as a “rat” or as a ‘‘ mouse.”
Zoologists, however, tend to restrict still further the use of these
names; they have divided the Muridae into several sub-families,
of which the principal are the Microtinae or Voles and Lemmings,
the Cricetinae or Hamsters, and the Mwurinae or true Rats and
Mice. The leading character of each of these sub-families is seen
in the cheek-teeth,* and for our present purpose they may be
sufficiently distinguished as follows :—

Cheek-teeth with tall prismatic crowns, in most genera per-
sistently growing and rootless; their grinding surfaces,
except when quite unworn, flat and displaying a pattern of
more or less alternating triangles (Figs. 2 D and 4 B-D).
MricrorTinak, or Voles and Lemmings.

* To examine the molars or cheek-teeth of Muridae in recently caught
specimens it is only necessary to cut as deeply as possible into the angles of
the mouth with a pair of scissors; the mouth can then be easily opened.

nl ates Pe ae Syren

;
:
i

as Enemies of Mankind. 51

Cheek-teeth with low crowns composed of rounded tubercles,
rooted and of limited growth.
Tubercles of upper cheek-teeth arranged in two primary
longitudinal series (fig. 4A). Cricrtrnar, or Hamsters.
Tubercles of upper cheek-teeth arranged in three
primary longitudinal series (Fig. 5). Murinan, or Rats
and Mice.

The natural distribution of these sub-families is interesting
and suggestive, for, coupled with the evidence of fossil remains, it
seems to indicate that the Muridae originated in the Old World
in early Tertiary times. The Cricetinae are the most ancient
and on the whole the most primitive of the sub-families; they are
now poorly represented in Europe and Asia, absent from Africa,
though represented in Madagascar by certain very lowly forms—
“living fossils’”—which are doubtless the little modified de-
scendants of the parent stock of the whole family. They are
widely distributed throughout the New World, where they have
developed many peculiar generic types. Neither in Madagascar
nor in America has this sub-family, or its allies, had to compete
with the Murinae until the most recent times. The Microtinae
also appear to be fundamentally rather primitive Muridae; they
have withstood the competition of the Muriae only in so far as
they have been able to acquire more earth-bound habits and the
power of living upon a hard diet of roots and coarse herbage ; they
seem to have originated in the temperate regions of Europe and
Asia and to have colonized North America by way of a former
land connection at the Bering Straits; unlike the Cricetinae, they
have not succeeded in entering South America. The Murinae
comprise many genera and are on the whole the most highly
developed and certainly the most successful members of the
family ; they have probably originated in the warmer regions of
the Old World, their range extending all through Africa and also
to Australia. They reached East Africa only after the separation
of Madagascar; and north-eastern Asia, in time to enter Japan,
but too late to cross to America. Neither the Cricetinae nor the
more generalized of the Mzcrotenae have been able to compete
with them successfully.

The living British Muridae belong to the sub-families
Microtinae and Murinae ; the Cricetinae also formerly inhabited
our country, but they became extinct here towards the close of the
Pleistocene period.

52 Rats and Mice

The Microtinae, or Voles and Lemmings, had many species
and genera living in Pleistocene Britain. Most of these forms are
now quite extinct here, although certain of them are still repre-
sented in continental Europe, or by more or less modified
descendants which linger on various small islands around our
coasts, as in the Orkneys and Hebrides. One of the most
astonishing features in the distribution of this sub-family is the
fact that, although remains of Lemmings occur in great abundance
in the Pleistocene cavern deposits of Ireland, there is apparently
no trace at all of either fossil or living Voles in that country.

In Great Britain itself three or four species of Vole are now
living. These may be distinguished as follows :—

A. Cheek-teeth (Fig. 4B) each with two well-developed roots or
fangs in adults. Lower molars with their triangles peculiarly
rounded, and not completely shut off from each other.

Size small (hind-foot 15:4 to 17°4 mm.*; condylo-basal
length of skull 21 to 24mm.). Tail densely haired, half as long
as head and body. Ears conspicuous above the fur.

Bank Voie, Evotomys glareolus. (Distributed through-
out the country.)

B. Cheek-teeth (Fig. 4C and D) persistently growing and never
developing roots. Triangles not rounded off, and from three to
five of them are completely shut off from each other in the
front lower molar. Ears not conspicuously projecting from
the fur.

a. Size small (‘Field Mice”). Tails about one-third the
length of head and body, less densely haired than in Evotomys.
Anterior lower molar with five closed triangles (Fig. 4 D).

1. Size relatively small (hind-foot 17 to 18 mm.). General
colour tawny russet.

SHortT-TAILED Fiexp Voue, Microtus hirtus. (Distributed
throughout England and the Lowlands of Scotland.)

2. Size slightly larger (hind-foot 18 to 19 mm.). General
colour darker and browner.

HigHLAND Fie~p Vous, Microtus agrestis neglectus.
(Distributed in the Highlands of Scotland.)

b. Size large (‘“‘ Water Rats’). Heavily built. Tail about
half the length of the head and body, its hairs nearly con-

* 25 millimetres = 1 inch.

as Enemies of Mankind. 53

cealing the scaly annulations. Anterior lower molar with
only three closed triangles (Fig. 4 C).

1. Size larger (head and body about 200 mm.; tail about
110 mm.; hind-foot usually 32 to 35 mm.). General colour
brown.

Common WATER VOLE, Arvicola amphibius amphibius.
(Distributed throughout England and Lowlands of
Scotland.)

2. Size smaller (hind-foot 30 to 32 mm.). General colour
black.

HiGHLAND WATER VOLE, 4. amphibius reta. (Distributed
in the Highlands of Scotland.)

In general our Voles are distinguished from our true Rats and
Mice by their heavier build, blunter muzzles, smaller eyes, shorter
ears, and comparatively well haired tails; the females of each
species have eight mammae, two pairs on the chest, two pairs in
the groin. The Bank Vole is our most primitive species; its
rooted teeth have been inherited with little change from the more
generalized ancestors of the sub-family; its diet is of a more
omnivorous character than is that of the more highly developed
voles. Our species of Microtus are highly specialized as feeders
upon grass and coarse herbage. The Water Voles are similarly
addicted to a hard diet; and they are, moreover, highly developed
for their aquatic existence.

The Murinae are represented in Britain by four genera;
these and their species may be distinguished as follows :—

A. First and second upper molars with three tubercles on the
inner side when unworn (Fig. 5 A-B).
a. Tail not prehensile, completely haired at the tip; orifice
of ear not closed by a special valve. Mammae in females six,
one pair being on the chest, two pairs towards the groin.

1. Size smaller (head and body about 95 mm.; tail about
90 mm.; hind-foot about 22 mm.; ear 15 to 17 mm.).
Lone-TarteD Fietp Mouse, Apodemus sylvaticus. (Dis-
tributed throughout Great Britain and Ireland.)

2. Size larger (head and body 100 to 115 mm. ; tail 105 to
125 mm.; hind-foot 23 to 27 mm.; ear 17 to 19 mm.).
De Winton’s Fretp Movss, A. flavicollis wintont. (Dis-
tributed through much of England.)

54 Rats and Mice

b. Tail prehensile, naked at the tip above. Orifice of ear
closed by a conspicuous valve. Mammae in females eight,
two pairs on the chest, two pairs in the groin. Size very
small (head and body 55to75 mm. ; tail 51 to 72 mm. ; hind-
foot 13 to 16 mm.; ear 8 to 10 mm.).

Harvest Movusez, Micromys minutus.

B. First and second upper molars with only two tubercles on their
inner sides.

a. Upper incisors (Fig. 3 a) with outer side of cutting edge
entire; front upper molar with five roots, its crown not so
long as the combined length of the succeeding teeth, and its
structure not peculiar (Fig. 5 D and E). Size large (Rats).

1. For external characters see p. 1.

Skull (Fig. 6 D) rather lightly and delicately built ; temporal
ridges not parallel, but strongly curved outwards on the sides
of the braincase; the length of a parietal measured along a
temporal ridge noticeably less than the greatest width between
these ridges ; parietal region with slight but noticeable con-
vexity when viewed in profile; condylo-basal length 38 to
45 mm., rarely more than 43 mm.

Buack Rat, Rattus rattus.

2. For external characters see p. 2.

Skull (Fig. 6F) strongly built; temporal ridges nearly straight
or parallel, never boldly curved outwards on the sides of the
braincase ; length of a parietal measured along a temporal
ridge about equal to the greatest distance between these
ridges ; parietal region flattened, without any conspicuous
convexity when viewed in profile; condylo-basal length 43 to
55 mm., rarely less than 45 mm.

Common Rat, Rattus norvegicus.

b. Upper incisor (Fig. 3 b) with outer side of cutting edge
broken by a conspicuous notch and projection; front upper
molar with three roots, its crown longer than the combined
length of the two succeeding teeth, and of highly peculiar
form (Fig. 5 C@). Size small (Mice). .

1. For external characters see p. 37.

Skull (Fig. 6 E) small and delicate; temporal ridges very
faintly indicated ; a strongly marked peg-like process of bone
on the lower surface of the maxilla immediately below the
anterior end of the infraorbital canal; the anterior palatal

as Enemies of Mankind. 55

foramina are very long, narrowing behind, and terminate

opposite the middles of the front molars (in all other British

species these foramina terminate in advance of the molars).
House Moussz, Mus musculus.

a. T.

Fic. 5.—Uprrer Incisors or Rattus (a) and Mus (b).
Much enlarged.

Of the four genera of Murinae dealt with above, two, Apodemus
and Micromys, are indigenous to Britain; the former, at all events,
was established in this country by the end of the Pliocene period.
As compared with the alien genera Rattus and Mus, they appear
to be less highly developed in many ways; in particular they have
retained a comparatively complex dentition. The Harvest Mouse,
nevertheless, is very highly specialized for its peculiar life among
the corn-stalks. This specialization is visible in the diminutive
size of the animal, and it is also betrayed in many of its organs,
e.g. in its foot-pads, which are modified for special use as
‘climbing irons.”

56 Rats and Mice

;
z

Gia ita :

TERZI

C. D.

Fic. 4.—CHEEK TEETH OF Cricetinae and Microtinae.

A. Hamster (Cricetus cricetus)—a, unworn, 0, slightly worn; B. Bank
VoLE (Evotomys glareolus), two individuals; C. WatTreR VOLE (Arvicola
amphibius); D. Fir~np VouE (Microtus agrestis). Enlarged (x 5). In
each case, the left-hand figure represents the molars of the right upper
jaw, while the right-hand figure shows those of the left lower jaw.

i cies a ee “ve
=e °

RINNE Cohen ast eg ieee, 3 eae Pe epee rar ee pe foe

as Enemies of Mankind. 57

Fic. 5.— CHEEK TEETH oF Murinae.

A. Lone-TaiLep FreLtp Mouser (Apodemus sylvaticus)—a, slightly worn,
b, much worn; B. Harvest Mouse (Micromys minutus); C. House
MovssE (Mus musculus); D. Brown Rat (Rattus norvegicus); E. BLACK
Rat (R. rattus). Enlarged (figs. A. B. and C. x 10; D. and E. x 5). In
each case the left-hand figure represents the molars of the right upper
jaw, while the right-hand figure shows those of the left lower jaw.

Rats and Mice

58

59

as Enenues of Mankind.

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shiwouupyt) TSAO ISHAUVH "OD ‘(sniqeydwy vjooasp) AIOA UMLVAA *G { (snoynarhs snumapodpy) ASHO{ CIAL AATIVI-DNOT *y

(‘ezIg TeInjeN) ‘appwnye ao STIANS—'9 ‘DI

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60

Rats and Mice

5. TABLE SHOWING RATE OF INCREASE IN
RAT POPULATION POSSIBLE IN 1918.

(The calculations are based on the assumptions made on p. 24.)

The following are the numbers of pairs of rats possessing a
chance of breeding which might be living at the dates specified, on
the assumptions indicated at p. 24 :—

| earl GENERATION 2,
0,000,000,
| Fitter 4:
9,208,334 10,000,000
8,416,668, 9,208,334
a et Litter 2.
7,625,000 8,416,668 | 8,416,668
6,833,336 2 7,625,000 | 7,700,000
—-—-———"| Litter 3.
| 6,041,670 | 6,833,336 | 7,050,000 | 6,833,336
| 5,250,000 4 6,041,670 | 6,400,000 | 6,300,000
— Litter 4.
4,458,338 | 5,250,000, 5,700,000 at 5,730,000 | 5,250,000
3,666,672 4,458,338 | 5,050,000 | 5,200,000 | 4,825,000
——- 4 Litter 5.
2,875,000 ' 3,666,672 4,400,000, 4,650,000 4,400,000 | 3,666,672
2,083,340, 2,875,000 | 3,750,000 | 4,100,000 | 4,000,000 | 3,370,000
Sn ee | ‘ Litter 6.
1,291,674 | 2,083,340 d 3,075,000 Pp 3,600,000, 3,600,000 3,080,000 |2,083,340
500,000, 1,291,674 2,400,000 | 3,050,000 | 3,150,000 | 2,800,000 1,900,000
GENERA-
GENERATION 3. Teche
Litter la. |
6,833,336 | |
6,300,000 | Litter 1b. Litter 2a.
5,730,000 | 5,250,000 — 5,700,000
5,200,000 | 4,825,000 Litter 1c. 5,230,000 | Litter 26.| Litter 3a.
4,650,000 | 4,400,000 3,666,672 , 4,775,000 | 4,400,000 | 4,650,000
aye ! Litterla-a.
4,100,000 | 4,000,000 3,370,000; 4,350,000 | 4,050,000 | 4,270,000 | 4,650,000
3,600,000, 3,600,000 | 3,080,000 | 3,900,000 3,700,000 | 3,900,000 | 4,270,000

as Enemies of Mankind. 61

Summary of possible Rat Population on December 31st, 1918 :—
Breeding Pairs.

Survivors of Capital Stock ; 500,000
" Generation 2, Litter 1 . 1,291,674

r3 ' SN ae 2,400,000

»» ‘i Dn 3,050,000

r» ss Se ag 3,150,000

r» * ei ara 2,800,000

r» “a | eis 1,900,000

r» ‘3 Cilio eee J 3,600,000

r» ‘- Pi tae 3,600,000

r» is es est Se 3,080,000

r» + ee! 3,900,000

% ii Se tate ee . 8,700,000

0 2 ~ Seas Rhee a . 3,900,000

= < ae he . 4,270,000
Pairs with a chance of breeding possibly ———--——
living on December 31st, 1918 ; . 41,141,674

Further, we might expect in early days of January, 1919, litters
in Generation 3 as follows :—

Litters 1d, 2c, 3b, and 4a; from these there might be a further
12,358,340 pairs with a chance of breeding.

Cost of maintaining breeding stock of rats (estimated at 4d.
per day per rat) :—

1918. Number of Pairs. Cost.
January . : 10,000,000 £645,000
February . 9,208,334 537,000
March ; 8,416,668 543,000
April . ; 7,625,000 476,000
May . 6,833,000 441,000
June . 12,874,000 804,000
July . ; 11,290,000 730,000
August : 15,408,000 981,600
September . 13,174,000 825,000
October 15,591,000 1,007,000
November . 17,458,000 1,090,000
December . 17,749,000 1,145,000

es

£9,224,000

62

10.

tS

Rats and Mice

6. LITERATURE

(in which many other references will be found).

De I’'Isle, A. De l’existence d’une race négre chez le Rat,
ou de lidentité spécifique du Mus rattus et du Mus
alexandrinus. Ann. Sct. Nat. (Zool.), Paris, 1865, iv.,
pp. 173-222.

Lataste, F. Recherches de Zooéthique sur les mammiféres
de l’ordre des Rongeurs. Bordeaux, 1887.

Zuschlag, E. Le Rat Migratoire et sa destruction ration-
nelle. Copenhagen, 1908.

Boelter, W. R. The Rat Problem. London (J. Bale &
Sons), 1909.

Lantz, D. E. The Brown Rat in the United States.
U.S. Dept. Agric., Biol. Survey, Bull. No. 33, 1909.

Board of Agriculture and Fisheries. The destruction
of rats. Leaflet No. 244, London, 1910; revised April,
1918.

Bulstrode, Martin and Rowland, Petrie and Mac-
alister. Reports and Papers on suspected cases of
human plague in Hast Suffolk and on an epizootic of
plague in rodents. Reports to the Local Govt. Board on
Public Health and Medical Subjects (N.S., No. 52),
London, 1911.

Miller, G. S. Catalogue of the Mammals of Western
Europe. British Musewm, London, 1912.

Barrett-Hamilton, G. E. H,, and Hinton, M. A. C.
A History of British Mammals. London, Parts XIY.
(1913) to XX. (in the press).

Anon. Rats and Rat Riddance. 62nd Ann. Rep. Massa-
chusetts State Board of Agric., Econom. Biol. Bull. No. 1,
December, 1914. 1915.

Elkington, J. S. C. A review of recent literature and
work on the epidemiology of Plague. Commonwealth of
Australia. Quarantine Service. Service Publication
No. 5. Melbourne, 1915.

12.

13.

14.

15.

16.

i¥

18.

as Enemies of Mankind. 63

Longman, H. A. Notes on classification of common
rodents with list of Australian species. Commonwealth
of Australia. Quarantine Service. Service Publication
No. 8. Melbourne, 1916.

Law, W. Destruction of Rats in East Lothian. Jowrn.
Board of Agric. and Iish., London, March 1916, p. 1238.

Board of Agriculture and Fisheries. Destruction of
Farm Vermin. Special Leaflet No. 52. London,
January 1916.

Sharpe, R. A series of papers on Rats and Rabbits.
The Fveld, London, January to March, 1918.

Gunther, R. T. Report on Agricultural Damage by
Vermin and Birds in Counties of Norfolk and Oxfordshire
in 1916.

Report of Departmental Committee appointed by Board of
Agriculture to inquire into a Puacur of Frenp VoLEs in
ScortanD. 1893 [(C.—6943].

Winge, O. Jegernes Skadelige Dyr. ed. 2 (H. Hagerup),
Kobenhavn, 1911.

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