Rats

What it is

Rats are larger rodents that live in close association with people. In the Mid-Atlantic, two species matter: the Norway rat (Rattus norvegicus), also called the brown rat or sewer rat, and, less commonly in the region, the roof rat (Rattus rattus). Oregon State University's pest guide describes rats as highly adaptable animals that thrive wherever food, water and shelter are available, and that is exactly what cities, suburbs and farms provide.

Norway rat habits

Norway rats are burrowers. They dig tunnel systems under sheds, porches, slabs, compost piles and along foundations. They are good swimmers and can travel through sewer lines. They mostly stay on the ground floor and in basements.

Roof rat habits

Roof rats are climbers. They nest in trees, attics, roof spaces and dense vegetation, and they travel along utility lines and branches. They are more common in warmer, coastal climates.

Reproduction

Rats breed rapidly. A female can produce several litters a year, with many young per litter, and the young reach breeding age in a few months. Populations can grow quickly when food and shelter are abundant.

Behavior

Rats are cautious and observant. They are wary of new objects in their territory (neophobia), they learn quickly, and they are active mostly at night. They have strong gnawing instincts because their incisors never stop growing.

How to recognize it

The animal

• Norway rat: a heavy-bodied rat, about 7 to 9 inches in body length, with a tail shorter than the body. It has a blunt nose, small ears and coarse brown-gray fur.
• Roof rat: sleeker, with a pointed nose, large ears and a tail longer than the body. Fur is black to brown-gray.
• Young rats vs. adult mice: a young rat has a large head and feet in proportion to the body. A mouse is much smaller and has proportionally large ears.

Signs of rats

• Droppings: larger than mouse droppings. Norway rat droppings are capsule-shaped with blunt ends, around a half to three-quarters of an inch long. Roof rat droppings are smaller and spindle-shaped with pointed ends.
• Gnaw marks: larger and rougher than mouse marks. Rats gnaw wood, plastic, lead pipes and electrical wires.
• Burrows: holes about 2 to 4 inches wide along foundations, under slabs and next to structures, often with smooth, worn soil around the entrance.
• Runways and rub marks: greasy dark smears along walls, pipes and beams where rats travel. Worn paths in grass.
• Noises: scratching, gnawing, running, or squeaking in walls, ceilings or attics, particularly at night.
• Nests: shredded paper, insulation and fabric in hidden spaces.
• Tracks and tail drags in dusty areas.
• Smell: a strong ammonia-like odor in a heavy infestation.

Look-alikes

• House mice are much smaller. See the mice page.
• Squirrels and chipmunks are active in the daytime and are rarely a household problem except in attics.
• Muskrats and voles live near water or in lawns.

Where you will find it

Outdoors

Look for burrows along foundations, under decks, sheds and concrete slabs, and in dense vegetation, woodpiles and compost heaps. Rats are drawn to unsecured trash, pet food, birdseed, fallen fruit, and gardens. Spots near waterways, restaurants and dumpsters are especially attractive.

Indoors

• Basements, crawl spaces and wall voids (Norway rats)
• Attics, upper floors and ceiling spaces (roof rats)
• Garages, sheds, barns and pet-food storage areas
• Kitchens and pantries in more serious infestations

How they get in

Rats can enter through gaps about the size of a quarter, and they can gnaw to enlarge openings. They use damaged vents, gaps around pipes and doors, broken foundation, drain lines, and open garage doors. They are strong, can climb rough surfaces, and Norway rats can swim through plumbing.

Seasonality

Rats are active all year. They push into buildings more in colder months, and populations often rise in late summer and fall.

Why it matters

Disease

Rats can spread disease through bites, contaminated food and water, urine and droppings, and ectoparasites like fleas. Illnesses associated with rodents include leptospirosis, salmonellosis and rat-bite fever. CDC also notes that some rodents carry hantaviruses, which people may contract by breathing in contaminated dust from urine, droppings or saliva. Anyone cleaning rodent-contaminated areas should take precautions.

Property damage

Rats gnaw on wood, plastic, insulation, pipes and electrical wiring, which can cause leaks, short circuits and fire hazards. They damage stored goods and foods, and burrows can undermine slabs, walkways and foundations.

Contamination

A rat can contaminate far more food than it eats. Droppings and urine in food storage or preparation areas pose a health risk and can lead to discarding food.

Fleas and mites

Rats can carry fleas and mites. If rats die or are removed, these parasites may move to people and pets.

What to do

Remove food and water

• Store trash in heavy, tightly closed containers, and keep dumpster lids closed.
• Feed pets in the daytime and don't leave food out overnight.
• Keep birdseed in sealed containers, and clean up spilled seed. Consider whether a bird feeder is attracting rodents.
• Pick up fallen fruit, nuts and garden waste. Keep compost bins secured, and avoid putting meat, grease or cooked food in open compost.
• Fix leaking faucets, pipes and standing water.

Remove shelter

• Reduce clutter and debris in yards, garages and sheds.
• Store firewood and lumber off the ground and away from the house.
• Trim trees and shrubs away from roofs and walls, especially for roof rats.
• Keep grass and weeds cut short around the foundation.

Inspect for entry points

Walk around the building and note gaps around pipes, vents, doors, utility lines and the foundation. Check the roofline and the attic for gaps. Listing the locations helps a professional plan exclusion and treatment in the correct order.

Cleanup safety

When cleaning rodent droppings or nests, do not sweep or vacuum dry material. Ventilate the area, wear gloves, wet the material with disinfectant, wipe with disposable towels, bag and discard, and wash your hands. For heavy contamination or confined spaces such as attics and crawl spaces, a professional should do the cleanup.

What not to do

• Don't set out poison. Rodenticides pose a real risk to children, pets and wildlife, and poisoned rats can die in walls. Secondary poisoning of owls, hawks and pets is well documented.
• Don't seal entry points while rats are inside. They may be trapped, die in the walls, or chew a new exit.
• Don't handle rats, dead or alive, with bare hands. Rats bite when cornered.
• Don't expect repellents or ultrasonic devices to solve the problem.

When to call a professional

Rats are a pest that is best dealt with by a licensed professional. They are wary of traps, they breed quickly, and the tools for controlling them safely need training.

Call a pest professional if

• You see rats, burrows, droppings or gnaw marks.
• You hear scratching in walls or the attic.
• You have rats near a food area or in the building.
• You have tried to trap them and the signs continue.
• Your property backs onto a waterway, restaurant or dumpster, and rats keep returning.

A professional will identify the species, find burrows and entry points, and plan the correct sequence of control and exclusion, with follow-up. Ask about sanitation and structural fixes that can reduce repeat problems.

Call a doctor if

• You are bitten or scratched by a rat. Wash the wound with soap and water and seek medical advice.
• You develop fever, muscle aches, headache, vomiting, cough or trouble breathing after exposure to rodents or their droppings. Tell your doctor about the exposure.