Identification
Heavy body, blunt nose, short tail.
Norway rats are the larger of the two rat species present in Seattle. Their heavy, stocky build and blunt nose distinguish them from roof rats, which are slender with pointed noses and longer tails. If you see a rat during the day, it is almost certainly a Norway rat, as roof rats are primarily nocturnal and far less likely to venture out in daylight.
Behavior and Biology
Burrowers, not climbers.
Norway rats live at ground level. They burrow under concrete slabs, decks, compost bins, and crawlspace foundations. A Norway rat colony typically has a primary burrow system with multiple entry and escape tunnels, often extending several feet horizontally under a structure.
They are omnivores with a preference for dense, high-calorie foods. Compost bins, pet food left outside, fruit trees, and chicken coops are their primary attractants in Seattle residential areas. They are food-motivated rather than shelter-motivated, meaning removing food sources is one of the most effective long-term deterrents.
Breeding is continuous indoors. A female Norway rat produces five to six litters per year with six to twelve pups each. Pups reach sexual maturity in three months. An established indoor colony doubles in size every two to three months without intervention.
Norway rats are neophobic: they avoid new objects in their environment for days. This is why freshly placed traps often catch nothing for the first week. We account for this in our trap placement strategy and timeline.
Signs of Infestation
What Norway rat activity looks like.
- Burrow openings (2 to 4 inches wide) near foundation, deck, or compost
- Droppings concentrated along walls, behind appliances, in the crawlspace
- Grease marks (rub lines) along base of walls and around pipe penetrations
- Scratching or thumping sounds from crawlspace or wall voids at night
- Ammonia odor from crawlspace vents
- Disturbed soil and fresh dirt mounds near the foundation
- Gnaw marks on wood framing, pipes, or conduit in crawlspace
Our Removal Strategy
Species-specific exclusion and trapping.
Norway rats require exclusion at the foundation and crawlspace level. They do not access buildings from above, so our work focuses on the ground-level perimeter: foundation vents, pipe penetrations, sill plate gaps, and burrow entry points under the structure.
Trap placement is at ground level: behind appliances, along wall runs in the crawlspace, and inside wall voids where access allows. We use large snap traps appropriate for Norway rat body size. Timing accounts for neophobia by giving traps three to five days before the first check.
We never use bait stations as a standalone treatment. Rodenticide kills rats but leaves carcasses in walls and crawlspaces. The decomposition process takes two to four weeks and attracts blow flies. Trapping lets us remove every carcass and confirm the total catch.
Call (206) 555-0188Questions about Norway rats.
How do I tell Norway rats from roof rats?
Norway rats are heavier with blunt noses and short ears. Their tails are shorter than their bodies. Roof rats are sleeker with pointed noses, large ears, and tails longer than their bodies. Norway rats burrow at ground level. If sounds come from under the floor or deck, it is almost certainly Norway rats. Sounds from the ceiling suggest roof rats.
Why are Norway rats so common in Seattle?
Seattle's moisture, older housing stock, and active compost culture create ideal Norway rat habitat. Wet climate keeps soil soft for burrowing. Old sewer lines offer movement corridors. Compost bins and fruit trees provide reliable food. Neighborhoods with mature landscaping and pier-and-beam foundations see the highest activity.
Do Norway rats carry disease?
Yes. Norway rats carry Leptospirosis, which spreads through urine in water or wet soil. They also carry Rat-bite fever and various intestinal pathogens. In Seattle, the greatest exposure risk comes from handling contaminated soil near burrows or from urine contaminating standing water in crawlspaces.
Can Norway rats chew through concrete?
They cannot chew through solid poured concrete but can enlarge existing cracks and exploit gaps in block foundations. They can chew through wood, plastic, aluminum flashing, and rubber. Steel mesh and galvanized hardware cloth is the appropriate material for exclusion.
Are Norway rats active in winter?
Yes. Norway rats do not hibernate. Winter drives more activity inside structures as outdoor food sources become scarce. The October through February period is when most Norway rat calls come in across King County.