Some information about
rats and mice
Two species of rat have inhabited
Europe for centuries. Some pest control historians believe
that the lighter, more agile, and longer tailed ship rat or
roof rat (Rattus rattus) has been around since at about the
7th Century, others say it has been here ‘since time
immemorial’. The date of the arrival of the heavier,
more aggressive brown rat or sewer rat (Rattus norvegicus)
is similarly disputed. Some say it first arrived with the
return of the ships during the crusades in the 12th Century,
others claim it turned up in the 17th Century. Gradually the
‘sewer rat’ displaced the ‘ship rat’
from our countryside, towns and cities, though colonies still
survive in a few of our major port cities. You can see that
names can be deceiving!
The house mouse is believed
to have come here from central asia where it lived mainly
on the seeds of wild grasses. The pest species is primarily
the house mouse (Mus domesticus) and should not be confused
with field mice, shrews and voles.
Some interesting habits
• Places where they can
live – Rats (R. norvegicus unless otherwise stated)
and mice (M. domesticus unless otherwise stated) are highly
adaptable and we have found nests in places as varied as oven
linings and industrial freezers. Rats will burrow 1-2m into
the ground and live in compost heaps, deep litter and of course
sewers. Mice can climb up breezeblock and rendering, telephone
cables and curtains and can get through gaps no bigger than
the thickness of a pen!
• Diet – Rats need
to drink water but mice can survive on the water content of
stored grain (approx 12 -14%) without ever having to drink.
A rat will take all its food (approx 30gm/day) from just one
or two locations and will feed once or twice a night. A mouse
will feed from as many as 50 different locations in a night
taking as little as 1/10th of a gram from each. Very important
in relation to bait treatments and cleanliness!
• Reproduction –
A female mouse can conceive 24Hrs. after giving birth and
will produce her litter in 21 days. A litter will contain
between 4 and 16 young. Young reach sexual maturity in 3 months.
Theoretically then two mice on January 1st could become over
1,800 by Dec. 31st! Fortunately natural mortality rate can
be as high as 90%. Rats usually produce between 4 -7 litters
per year with an average litter size of 7-8.
• The Hazards - Rats have
brought us the plague and weil’s disease, and both species
have been responsible for outbreaks of food poisoning. They
dribble urine upon everything on which they walk and so contaminate
bulk food stocks and food preparation surfaces wherever they
go. Mice produce up to 80 droppings per day. They must gnaw
hard surfaces to keep their constantly growing incisor teeth
short. They damage electricity cables, lead pipes, wood, plastic
and wet cement.