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Rats and mice are habitually nocturnal and secretive and are
rarely seen during the day except when infestations are heavy.
Therefore, to plan control work, it is necessary to properly
interpret signs of their activities. These signs are found in
secluded places, such as along walls, under piles of rubbish and
behind or under boxes, boards and thick vegetation. From
the rodent signs, one can tell the species present and whether a
rodent infestation is current or old, heavy or light.
 Droppings. Fresh droppings of feces usually are moist,
soft, shiny and dark, but in a few days they become dry and
hard. Old droppings are dull and grayish and crumble when
pressed with a stick. The roof rat's droppings are up to
1/2 inch long, spindle shaped and curved in contrast to Norway
rat droppings which are about the same length but comparatively
blunt. Mouse feces are small, Averaging about 1/8 inch
long, and are pointed on both ends.
 Runways. Rats habitually use the same runways
between food, water and harborage. Because of the keenly
developed sense of touch in their vibrissae (whiskers) and in
specialized hairs along the body, rats prefer continual body
contact with at least one vertical surface such as a fence or
wall. Rats also follow "odor trails." Outdoors,
their runways are narrow pathways of beaten earth swept clear of
debris. Indoors, greasy runways are found along walls,
steps and rafters. Undisturbed cobwebs and dust in a runway
indicate that it is not in use.
 Rubmarks. Along regularly traveled runways, a
dark, greasy mark forms from contact with the rodent's body.
Fresh marks are soft and smear if rubbed. As the grease
ages, it dries, gathers dust and flakes off when scratched with
a fingernail. Rubmarks of the Norway rat are most commonly
seen overhead as swing marks beneath beams or rafters where they
connect to the walls. Mice do not have detectable rubmarks
except when the infestation is heavy.
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Burrows. The Norway rat prefers burrows for
nesting and harborage; the roof rat burrows only occasionally.
Burrows are found in earth banks, along walls, under rubbish or
concrete slabs and in similar places. If a burrow is in
use, its entrance is free of cobwebs and dust. Fresh
rubmarks on hardpacked soil at the opening indicate a well
established and presently used burrow. Fresh fragments of
food or freshly dug earth at these burrow entrances also current
use by rats.
Gnawings. The incisor teeth of rats grow 4 to 5 Inches
a year, so these rodents must do some gnawing each day to keep
their teeth short enough to use. Rats also gnaw to gain
entrance and to obtain food. When gnawings in wood are
fresh, they are light colored and show distinct teeth marks.
Small chips of wood or other materials indicate recent gnawing.
With age, wood gnawings become dark and smooth from weathering
and from frequent contact with the rodent's body.
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Tracks. Fresh tracks are sharp and distinct,
whereas old tracks are covered with dust and are less distinct.
Tracks of the five-toed rear paws are more commonly observed
than are those of the four-toed front paws, but both may be
present. Smooth patches of any dust material, such as
flour or talc, placed along runways are valuable for checking
rodent activity. To see tracks in the dust, hold a
flashlight at an angle where tracks cast distinct shadows.
Tail marks, too, are often visible in dust or tracking patches.
Urine. Dried rodent urine will fluoresce bluish
white to yellowish white. Commercial black lights often
are used to detect rodent urine, however observing fluorescence
is not a guarantee that rodent urine is present. Numerous
items will fluoresce under a black light, including optical
bleaches found in many detergents and lubricating oil. For
positive identification use a Brom Thymol Blue Urease Test.
Place the suspected material on Urease-Brom Thymol-Blue test
paper. Moisten with water and cover with a glass. If
a bluish spot appears after 3 to 5 minutes, it is rodent urine.
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Home range. Rats and mice usually spend their
lives in a very limited area called their home range, which is
no larger than necessary to provide the necessities of life
(food, cover and water). An individual moves from its home
range only when necessary. Under favorable conditions home
range might be less than 10 feet in diameter; under less
favorable conditions it may be up to 150 feet. Rats
generally range further than mice. This information
affects placement of a rodenticide bait station or traps within
the home range of an individual.
Sounds. Gnawing, clawing, climbing in walls,
squeaks and fighting noises may be heard.
Visual sighting. Observation of rats in daylight
generally Indicates a high or moderately high population in the
area. Night observations with a powerful flashlight or
spotlight often are helpful.
Nests and food caches. These can sometimes be
found when cleaning garages, attics, basements, closets and
other storage places. Roof rats, as well as other rodent
species (i.e., squirrels and packrats), often store food in
attics. Roof rat nests may be exposed when dense
vegetation is pruned or removed from an infested area.
Rat odors. Rat odors in a room may provide a
clue to their presence. With a little experience, the
odors of house mice (Mus musculue) can be differentiated readily
from those of rats.
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