Description
Ratus norvegicus, the brown rat, is known by many different
names including the sewer rat, common rat and the Norway rat.
An average adult rat weighs approximately 300 g and is
approximately 30 cm long from nose to tail.
Biology and Habitat
Rats are capable of reproducing at the age of about three
months. Pair bonds are not formed as mating is carried out on
an opportunistic and promiscuous basis. When a female becomes
receptive, her scent attracts all the local males. The female
is sexually receptive for a relatively short time (about 12 hours)
each cycle. Mating is brief and can take place with a number
of males. After mating and conception there is the period of
pregnancy (gestation) of about three weeks.
New litters are born blind, without hair and are totally
helpless. They become fully furred at about two weeks old,
with eyes and ears open and incisor teeth showing. The
litters are weaned at about three weeks old and are sexually mature
at about three months old, and so the cycle continues.
The rat is capable of producing about four to six litters in a
year. A litter can consist of anything from six to eleven
young, however many of the young die before reaching sexual
maturity.
The period of time from birth to the natural death of the rat is
dependant on several factors. In the laboratory rats have
been know to live for two years or more, but under natural
conditions it is likely that less than 10% survive for more than 12
months.
Rats are natural burrowers, which assists in the need for
harbourage. These have many functions; it acts as a place to
rear young, to rest or to escape from predators.
Rats have a well-developed sense of smell, hearing and touch,
but they cannot see very well. They are colour blind and,
compared with other senses, sight seems to play only a minor role
in their lives.
Importance
The infamous Plague, caused by a bacterium that was transmitted
to man from rats mainly via the rat flea, is hopefully confined to
the history books.
Weils disease, caused by the bacterium leptospira
icterohaemorrhagiae, is shed in the urine of the infected
rats. Another disease which is significant is salmonellosis,
caused by bacteria of the salmonella group. It is one of the
most widespread of animal borne diseases. Infection in humans
commonly occurs from the contamination of food and/or drinks with
rodent excreta. Other rodent borne diseases include rat bite
fever, lymphocytic choriomeningitis and murine typhus.
Control
Before attempting to control an infestation of rats, it is
important that a pest survey is carried out to identify the extent
and size of the infestation, areas of activity and possible baiting
points, food sources, water sources, harbourages, the history of
infestations in the area, proofing defects, hygiene defects and non
target hazards.
Signs of rodent activity include sightings, smell (a
characteristic stale odour) and droppings (on average 12 mm long
and spindle shaped). Fresh droppings appear soft and shiny,
but within a few days they become hard and dull. Also, rats
tend to follow the same route when moving about, so rat runs are
easily detectable to the trained eye, as are the smear marks left
from the coat of the rat.
Various methods of control are available to the pest control
officers, the most popular being the use of a range of rodenticides
and/or trapping, depending on the nature of the infestation.
Proofing and damage prevention is also very important in the
treatment of all pests.
Safety
All pesticides used by Bath & North East Somerset Council
are approved substances under the Control of Pesticides Regulations
1986 and are fully risk assessed.
