and Rattus norvegicus
Management of rats and other
rodents always begins with a systematic survey and evaluation of the potentially
infested site. Estimates of pest numbers and a map of the infested site
should be generated. The potentially infested site should be cleaned,
removing all possible food sources for the rodents. The site should be
altered to eliminate all favorable nesting habitat and to eliminate any
passageways that might exist form outside points into adjacent structures.
When a structure is infested, intense trapping, using large numbers of
traps should be attempted along with the structural and habitat modifications.
All park staff and visitors should be fully informed of the mission of
the control effort and the reasons for the infestation. These cultural,
mechanical, and physical methods of addressing a pest problem should always
be carried out before the use of a chemical is considered.
light brown to dark gray; occasionally a little lighter on the belly
to 7 inches, ½ to 1 ounce, slender, agile
ears, small feet and eyes in proportion to the body; sparsely hairy
brown to black
to 18 inches (including tail), 12 to 16 ounces, stocky, ears are small
is shorter than its head and body length, is a larger, heavier rat,
with smaller eyes and a blunter snout than the roof rat, dropping
are large and ovoid.
brown to Black
to 18 inches (including tail), 5 to 9 ounces, slender, ears are large
and nearly hairless.
is longer than its head and body length, thinner and lighter than
Norway rat, droppings are long and cylindrical.
Roof rats and Norway rats have
similar Life Histories and habits. Where differences are important for
management purposes, however, the differences will be highlighted. Rats
have poor vision. Rats are wary of anything new that appears in their
territory, avoiding the new object for a few days until the rats become
familiar with it.
Life cycle: A mature
female rat can give birth to about 20 young in a year (4 to 6 at a time).
The average life span of a rat in the field is less than one year, with
females living longer than males. The young are born in nests. They are
hairless and their eyes and ears are closed. Within two weeks their eyes
and ears open, they grow fur, and they begin exploring the nest area.
In the three week they begin to switch to solid food, and imitate their
mother to learn pathways to food, escape routes, and danger zones. If
the mother rat has become wary of rodenticides or traps, many of her young
will learn to avoid them. This learning experience can make management
difficult in sites where long-term rodent suppression programs have been
unsuccessful in the past.
Young are totally weaned when
4 or five weeks old. They then weigh about an ounce and a half. At three
months the young are independent of their mother and able to mate and
continue the cycle, either in the same location or after migrating to
a new, unoccupied are.
Outdoor populations tend to
peak in summer to early fall. Indoor populations may remain at the same
levels throughout the year, limited only by periodic shortages of food,
water, or nesting sites.
Social Behavior: Rats
are social animals and live in colonies with well defined territories
that they mark with urine and glandular secretions. Rats are aggressive,
and social conflicts are most common at feeding sites, prime nesting sites,
and territorial boundaries. Females fiercely defend their nest and young
from other rats.
that favor development: The Norway rat and the Roof rat have different
nesting and feeding preferences that should be considered when management
programs are formulated.
environmental conditions needed
outside in trees, woodpiles and debris, and in dense vegetation. Inside,
roof rats prefer to nest in the upper levels of a building in the
attic and ceiling
more vegetarian preferences. Typical food is fresh plant material,
nuts and seeds, fruit and vegetables and tree bark.
isolated nesting site near water and food sources.
either inside or out; Outside, they form burrows usually less than
18 inches deep. Also nest in sewers and storm drains. Nests inside
are found in lower floors, crawl spaces, storage rooms and/or in any
cluttered area that is little used.
likely to eat garbage than roof rats. High protein foods such as fish,
meat, nuts, grains, pet food and insects.
nesting sites within 100 feet of water and food sources.
Natural Enemies: Dogs,
cats, snakes, birds of prey, and other rats.
Medical importance: Rats
can spread disease. Sometimes they transmit disease directly by contaminating
food with their urine or feces or by biting people. Sometimes they transmit
disease indirectly, as when fleas bite a disease-infected rat, then a
person. Some of the important diseases associated with commensal rats
are: Plague (not currently a problem in the NE USA), Rat-Bite
Fever (a seldom serious bacterial infection that occurs occasionally
after being bitten by a rat.), Salmonella Food Poisoning (a problem
where rats have access to human food sources), and Leptospirosis (another
disease that is spread to humans through contaminated food, water, and
through cuts in the skin).
Potential Damage: Rat
burrows can cause structural damage by undermining the foundations of
buildings, roads, and walkways; can cause damage by gnawing, damaging
plastic and lead pipes, door frames, upholstery, and electric wires; and
cause damage through the destruction and contamination of food crops and
Threshold: The Roof
and Norway rats are not native to the United States and are thus considered
to be exotic. For that reason, the sighting of just one Norway or Roof
rat is adequate reason to initiate management efforts addressed at eliminating
the rats. Management efforts should continue until all visible signs of
the rats are absent. Monitoring for the detection of a new rat infestation
should continue year-round.
is a systematic survey conducted at regular intervals.
- Keep good monitoring records
of what you see, smell, hear, and when you saw it, and under what conditions
you saw it. These records are important in determining how to best manage
- Visual Sightings
- an inspection using a powerful light, just after dark, is the best
way to see rats. If you see rats during the daytime, population levels
are very high!
- Sounds - when it
is quiet in a building, you can sometimes hear squeaks, fighting noises,
or clawing and scrambling in the walls. A stethoscope can help pinpoint
- Droppings - A single
rat may produce 50 droppings daily. One way to determine if a rat population
is active is to sweep up old droppings and reinspect a week later for
new droppings. Fresh rat droppings are black or nearly black, wet and
may glisten, and soft. Older droppings lose the black coloration.
- Urine - Both wet
and dry urine stains will glow blue-white under an ultra-violet light
(blacklight). Blacklight inspections work best at night and in dark
- Grease marks - Oil
and dirt rub off of a rat’s coat when it rubs against things. These
grease marks build up in often used runways and soon become noticeable.
These marks are commonly found along wall/floor junctions, on pipes
and ceiling joists, and on sill plates.
- Runways - Outdoors,
runways tend to appear as beaten paths on the ground where rats constantly
travel the same route. These can be found next to fences, under bushes,
and along buildings.
- Tracks, Gnawing damage,
burrows - physical signs or damage are important indicators of the
presence of rats, the size of the population, and the location of the
infestation. A tracking patch (a light dusting of an inert material
such as clay, talc, or limestone) can be place in sites where you suspect
rat activity. The rats walk through the dust and you will be able to
track the pests movement. The size and number of burrows is a useful
indicator of the significance of the infestation.
Tools needed for Monitoring:
A flashlight; ultraviolet light; talc; map of the site showing important
observations; monitoring record form or sheet.
any or all of these recommendations as needed
instructional information and guidance in the area of Rodent pest
management, including garbage and trash handling and proper site maintenance
avoid open areas!
mowed to about 2 ½ inches.
piles of building materials, and other items that might serve as
a hiding or nesting site.
and other low plants pruned, so monitoring is easy.
Make sure all
trash and garbage storage cans and container are metal with tight
fitting metal lids.
rat harborage inside an infested structure, clean out all food,
clutter and debris that might exist inside the building. After cleaning
the structure, make sure that all food residues are removed and
that any remaining foods are stored in rat proof containers.
initial stages of the Rodent IPM effort.
early stages of the Rodent IPM effort.
most effective form of rat management in structures is "rat proofing";
fixing a building so that there are no easy paths for the rats to
can squeeze through a slot-like opening ½ inch high.
To rat proof
- Block all
opening around pipes, utility lines, and air vents.
- Doors and
windows should be tight fitting.
- Seal holes
and cracks in the foundation.
- Repair roof
soffits and seal all openings on the roof.
- Repair gnaw
holes as they occur, using steel wool to plug the hole before
- Cover all
floor drains with mesh.
- Fill all
interior and exterior holes to prevent movement of rats in walls.
with the park cultural resources personnel to assure that all compliance
issues are addressed before beginning any site modification activities
on a Historic structure
Rat proofing activities begin
snap trap is an effective method of managing rats when properly placed.
- Leave traps
unbaited for a few days to allow the rats to get used to them.
- For Norway
rats, used peanut butter, bacon, fish, or nut meat as a bait.
- Roof rats
can be baited with dried fruits and nuts or fresh fruits such
as banana or apples.
- If one bait
does not seem to be working, try another.
- Place traps
where ever you have seen signs of rats (along runways, at the
site of droppings, along the wall where markings are seen). Place
the traps in groups of threes, with about ten feet between groups.
- Traps should
be placed wherever runways exist, including over head if pipes
and rafters are being used.
trapping for about two weeks.
- EMPTY TRAPS
AT LEAST ONCE A DAY!
examining the infested site to determine runways, and other sites
for trap placement. The site should also be cleaned up before can
be expected to work.
trapping not usually a option with rats. However, if non-target species
are potential threatened, Live traps can be used.
Rodenticides should not be
used indoors in NPS facilities, particularly in historic buildings, except
under extreme circumstances. Rodents that have ingested a toxic dose of
a rodenticide may crawl into wall voids and other inaccessible areas to
die. The decaying carcass can produce foul odors and attract insects such
as dermestid beetles or blowflies, which feed on the dead animal. Once
they have consumed the carcass, the insects will seek other food sources,
and may become pests themselves, feeding on fabrics, furs, stored foods,
and historic artifacts.