method. These methods can be found in the
Official Methods of Analysispublished by the
Association of Official Analytical Chemists
or in other specialized analytical publications.
Insects, insect fragments, eggs, larvae, and
chrysalises should be identified, counted, and
recorded to permit immediate pinpointing of
dangerous infections or the appearance of
abnormal variations. The same should be
done for rodent hairs and excrement.
Rodents
Rodents such as rats and mice are difficult
to control because they have highly devel-
oped senses of hearing, touch, and smell.
These pests can also effectively identify new
or unfamiliar objects in their environment
and protect themselves against these changes
in the surroundings.
Rats
Rats can force their entry through open-
ings as small as a quarter, can climb vertical
brick walls, and can jump up to a meter ver-
tically and 1.2 meters horizontally. These
rodents are strong swimmers and are known
for their ability to swim up through toilet
bowl traps and floor drains.
Rats are dangerous and destructive. The
National Restaurant Association has esti-
mated that the loss from rodent damage
could be as high as $10 billion per year. This
includes consumption and contamination of
food and structural damage to property,
including damage from fires caused by rats’
gnawing on electrical wiring. Of greater
importance than economic losses from rat
infestation is the serious health hazard from
contamination of food, equipment, and
utensils. Rats directly or indirectly transmit
diseases such as leptospirosis, murine typhus,
and salmonellosis. Several million harmful
microorganisms can be found in one rat
dropping. When droppings dry and fall
apart or are crushed, the particles can be car-
ried into food by air movement within a
room.
The most abundant kind of rat in the
United States is the Rattus norvegicus(Nor-
way rat), a red-brown to gray-brown rodent,
sometimes known as the sewer rat,barn rat,
brown rat, or wharf rat. Norway rats are nor-
mally brown, and are 18 to 25 cm long,
excluding the tail, weigh 280 to 480 g, have a
rather blunt nose and a thick-set body, and
tend to live in burrows. A rat generally found
in the South and along the Pacific coast and
Hawaii is called the Rattus rattus(roof rat).
This rat, which seeks an elevated location for
its habitat, has more coordination than does
the Norway rat and is smaller. It is black to
slate-gray, 16.5 to 20 cm long, excluding the
tail, and weighs 220 to 340 g. Roof rats will
burrow or create nests in trees, vines, and
other locations above the ground.
The female rat becomes fertile within 6 to
8 weeks after birth and can produce 6 to 8
young per litter, 4 to 7 times per year, if con-
ditions are optimal for reproduction and sur-
vival. The typical female weans an average of
20 offspring per year.
Rats that receive an adequate amount of
food will usually not move more than 50 m
from their nest if mates are available. How-
ever, rat populations will adjust as food
becomes scarce in one location or as a portion
of the population starts to die from eradica-
tion methods. Rats and mice instinctively
avoid uninterrupted expanses, especially if
this potential barrier is lightly colored. There-
fore, a potential rodent deterrent can be cre-
ated by the construction of a 1.5-m-wide
band of white gravel or granite chips around
the outside perimeter of a building.Mice
Mice, found frequently as the Mus muscu-
lus domesticusandM. musculus brevirostrisPest Control 245