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Gloucester City Council Factsheet

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					                           Gloucester City Council
                              Environmental Health
                                          Factsheet
                                 Public Health: Mice




         House Mouse

         The house mouse has been identified from pre-Roman Iron Age deposits and is believed to
         have arrived in Britain around the 10th Century BC. It is likely that it was once a wild
         species somewhere on the borders of the USSR and Iran, and gradually spread with the
         practice of agriculture.

         It is common in a wide range of urban and rural buildings all over Britain. Although mainly
         a house dweller, it may live outdoors for part or all of the year. It is not found in sewers.


         Appearance: House Mouse and other British Mouse Species

         As it is much smaller the house mouse should not be confused with the two rat species.
         Indeed, a newly weaned common rat will weigh more than an adult mouse. The young rat
         will also have a larger head and larger feet in proportion to its general body size, and its
         tail will be noticeably thicker.

         The house mouse may, however, be confused with three other species of mouse found in
         Britain, the wood mouse or long-tailed field mouse (Apodemus sylvaticus), the yellow-
         necked field mouse (Apodemus flavicollis) and the harvest mouse (Micromys minutus).
         Both species of Apodemus look most like the house mouse but prefer to live out of doors.
         They do sometimes enter houses, but can more commonly be found in sheds, garages and
         outhouses.




ENVIRONMENTAL HEALTH
Gloucester City Council   Tel 01452 396396 Fax 01452 396340
Herbert Warehouse         Email enviro@gloucester.gov.uk
The Docks                 Minicom 01452 396161
Gloucester GL1 2EQ        www.gloucester.gov.uk
Physical Characteristics

Teeth

The arrangement and form of their teeth distinguish rodents from other mammals. There
is a single pair of upper and lower incisor teeth, but no canine or pre-molar teeth. The
wide gap between the incisors and the molars or cheek-teeth is called the diastema. This
dental arrangement gives the rodent skull its unmistakable appearance.

Rodent incisors have three characteristics which together distinguish them from the
incisors of other mammals. They grow continuously throughout the rodent’s life, are
strongly curved and carry a thick layer of hard enamel on the outer side only.

To allow for continuous growth the incisors must also be worn away at a similar rate. This
is achieved by gnawing objects within their environment and by grinding the upper and
lower pairs together. Gnawing results in the softer dentine of the incisor being worn away
more readily than the hard outer layer of enamel. This forms an efficient chisel-like edge
to the teeth.

The curved shape of the incisors also imparts great strength to the bite. Mice, given an
edge on which to bite, can penetrate all types of wood as well as soft metals such as
aluminium and lead. The incisors project well beyond the lips so that the animal does not
have to ingest any of the substance being gnawed.

The molar teeth are used for grinding food into digestible sized pieces. Unlike the incisors
they do not grow continually but wear down during the life of the animal.

The measurements given in the table below for these two species show that the house
mouse is generally smaller. The yellow-necked field mouse is about one and half times the
size of the wood mouse. One infallible aid to identification is the characteristic notch in
the upper incisors of the house mouse.

The house mouse is very small (6-8g), rather blunt-nosed and small-eared. It is yellowish-
brown in colour and has a moderately long tail with a prehensile tip. It lives in fields and
hedgerows and makes nests among the stalks of cereals, grasses, reeds and sedges.

Physical dimensions of adult mice

                                House mouse                      Wood mouse
Weight                          Usually less than 25g (average   Usually less than 28g (average
                                15g)                             25g)

Combined head and body          70-90mm                          80-100mm
length

Length of hind feet             16-19mm                          20-23mm



Aspects of behaviour

Movement

In general terms, the directions in which a rodent moves depend upon the distribution of
its food, water and shelter (harbourage) as well as its interaction with other individuals of
the species.
In situations where food and harbourage are adequate, mice tend to have a restricted
home range (area of normal movement) and follow regular routes. Their ranges tend to be
smallest when they are living in areas such as food stores, where food and cover are
generally abundant.

In indoor habitats, the foraging ranges of house mice can overlap and be as small as 5
square metres. Individual mice will not move more than 3 to 10 metres in most buildings.
Despite this relatively static behaviour, expanding populations of rodents in urban areas
can rapidly exploit unoccupied areas and nearby premises.

New Object Reaction

A very important factor having a bearing on the control of rodents is their natural and
characteristic form of behaviour when encountering strange or new objects in their
environment. Rodents have an intimate knowledge of their surroundings.

The house mouse often exhibits initial cautious behaviour, followed by a rapid and
thorough investigation. Although house mice tend to investigate strange objects and food
sources relatively quicker than rats, their interest in them generally lasts for a shorter
time.

Grooming

Rodents are mainly nocturnal and most activities occur in the dark, although periods of
rest (as opposed to sleep itself) are about equal in light and dark. Sleep may make up 30%
of any 24 hour cycle, and the inherent behavioural characteristic of grooming occupies up
to 20% of their time. Grooming is a cleaning activity which involves licking the fur and
feet. Such behaviour makes possible the use of poisonous contact formulations which are
picked up on the fur and feet and ingested during grooming.

Food and Feeding

Diet

The house mouse is believed to have spread from grain-growing regions and cereal
products can constitute much of the diet. Consequently, many of the current formulations
of rodenticidal baits have a cereal bait base. They will consume an astonishing variety of
other foods, including vegetable matter of different kinds, meat, fish and insects. The
exact composition of an animal’s diet is dependent upon what is available locally but
house mice, in particular, are surprisingly indiscriminate in their choice of food. In urban
areas they eat many of the same foods as man. However, they seem to be particularly
attracted to small grains such as canary seed which they de-husk before eating and foods
moistened with vegetable oils are generally well received.

In some urban areas, mice have become unable to digest cereal based food and instead
prefer high protein foods they might not normally be thought to consume. Such house
mice have been termed “behaviourally resistant” because their avoidance of cereals
appears to be genetically based. They thrive and reproduce best in localities that provide
them with a rich and varied diet containing protein foods and least well on single items
lacking in essential vitamins.
Water

The ability of rodents to manage without free water varies according to species.

The house mouse can exist on very little water and its intake is largely regulated by the
moisture content of its food and the external temperature. It can live without drinking
water when the moisture in its food is about 15 to 16%. However, mice will often obtain
water by nibbling succulent foods such as melons, tomatoes and apples.

In food stores, mice may have access to water from dripping taps, blocked drains and via
leaking roofs - all defects which can be rectified. In dry situations, the rodents need for
water can be exploited by the use of liquid poison baits or by soaking whole grain baits to
make them more attractive.

Feeding Behaviour

House mice are light, intermittent and erratic feeders tending to sample from a large
number of different sites. This is one characteristic which has important consequences for
control as there is a need for a correspondingly large number of small bait points. It is
really a matter of taking the baits to the mice rather than attracting them to the baits. If
left undisturbed, mice will frequently feed during daylight hours.




                                                                                      EHF54
                                                                                    MAY 2002

				
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