Rats and Rodents in Washington State

Two rats, and neither of them belongs here

Washington has two rat species that live around people, and the Department of Fish and Wildlife names both: the Norway rat, also called the brown rat or the sewer rat, and the roof rat, also called the black rat.

Neither is native. Both are Old World rats brought to North America on early ships, and WDFW describes them as found wherever people have established permanent residence or industry. In a county with a port, a rail line, farms, grain handling and a university town, that means everywhere.

The practical difference between them is not academic. They nest in different places, they get in by different routes, and a plan built for one of them will miss the other entirely.

Norway rat or roof rat

The tail is the fastest check, and behavior confirms it.

Norway rat. The bigger, heavier, blunter animal. Its tail is shorter than its head and body combined. WDFW describes it as preferring to nest at or under ground level and in the lower floors of buildings, usually in burrows. In this county that means crawlspaces, under sheds and decks, along foundations, in compost and against the banks of ditches. The species page is at Norway rat, and the problem it most often produces is rats in the crawlspace.

Roof rat. Smaller, slimmer, with a tail longer than its head and body. It climbs, and WDFW describes it as building nests in attics, trees and overgrown shrubbery or vines, and rarely digging burrows where off-ground sites exist. WDFW also notes it prefers saltwater-influenced, warmer climates and is often seen in port cities and coastal towns — a fair description of Bellingham, Blaine and the waterfront. The species page is at roof rat.

That high-or-low split decides the whole job. A roof rat problem is solved at roof line, vent screens, overhanging branches and ivy on walls. A Norway rat problem is solved at ground level, foundation gaps, crawlspace vents and door sweeps. Doing the wrong one properly achieves nothing at all.

How fast a rat population actually moves

The numbers are the argument for acting early rather than watching.

WDFW gives the reproductive figures: litters of six to ten young, a gestation of about three weeks, weaning at around twenty days, and breeding age reached at three to four months. Breeding happens year-round and concentrates in the warmer months.

Set against that, WDFW puts the average life span of a wild rat at under a year. Both halves matter. A rat population is not a stable thing that sits still — it is a fast turnover that either grows or collapses depending on food, shelter and access. Which is why the durable fix is always the access, and why exclusion and repairs is the part of this work that lasts after the trapping is finished.

The native rodents people confuse with them

Three of them, and the differences change what should be done.

Deer mouse. Native, big-eyed, bicolored — brown above and sharply white below, with a tail to match. It is the rural and semi-rural mouse here: cabins, outbuildings, garages, seasonal homes. It is also the hantavirus one, which is covered below and is the single most important identification on this page.

House mouse. Introduced, uniformly gray-brown, small-eared, and the mouse of occupied buildings in town. The common urban rodent complaint in Bellingham, and the subject of droppings in the kitchen.

Vole. Native, stocky, short-tailed, blunt-faced, and almost never a building problem. Voles live in grass and work at ground level, and what they damage is lawn, root crops and the bark around the base of young trees and shrubs. WSU Extension publishes a management guide for exactly that problem. People call them field mice, and the two animals are not the same.

The quickest triage on droppings: rat droppings are the size of a raisin with blunt ends, mouse droppings the size of a grain of rice with pointed ends. That one observation decides most of what follows.

The hantavirus distinction, which is the reason to get the species right

Deer mice, not rats, and the handling advice differs.

The Washington State Department of Health’s hantavirus guidance is built around deer mice, and the risk comes from disturbing dried droppings, urine and nesting material in an enclosed space — a cabin, a crawlspace, an outbuilding, a shed that has been shut for the winter. The central instruction is not to sweep or vacuum dry. Ventilate first, wet the material down, and remove it wet.

That is a specific procedure for a specific animal, and it is the reason the first question on any rodent cleanup is which rodent. A Norway rat problem in a Bellingham crawlspace does not carry the hantavirus risk; the same looking mess in a Mount Baker-area cabin with deer mice in it does.

The rest of what rats do carry — WDFW lists plague, salmonella, leptospirosis and tularemia as able to pass from Old World rats to people — is a reason for gloves, sensible handling and a doctor after any bite or scratch, rather than a reason for alarm. Whatcom County Health and Community Services publishes local guidance on rodents and cleanup as well.

West and east of the Cascades

The split is real for rodents, and smaller than it is for some pests.

Both rat species occur statewide wherever there is human settlement and industry, so the east-west difference for rats is more about building stock and agriculture than about climate. What does change is the housing: this side of the mountains gives you vented crawlspaces, wet ground and wooden buildings in trees, which produces a very different rodent pattern from a dry-side property on a slab.

For deer mice the picture is about land use rather than longitude. They are animals of field edges, woodland margins and outbuildings, which means rural Whatcom and Skagit produce far more deer mouse work than central Bellingham does, and the seasonal cabins on the Mount Baker Highway produce the most of all.

What is ours and what is not

Worth stating plainly, because the search term pulls in a lot of animals we do not touch.

Ours. Rats, house mice, deer mice and voles — identification, trapping, exclusion, crawlspace and attic cleanup, and the repairs that keep them out. Rodent control sets out the work, and rodents in the attic insulation covers the most expensive version of it.

Not ours. Moles, squirrels, opossums, raccoons and birds. We do not do nuisance wildlife, we do not trap moles, and a job that turns out to be one of those gets referred rather than attempted. That is a deliberate boundary and it is listed openly rather than discovered after a visit.

If you are not sure which you have, the droppings, the location and the damage pattern usually settle it over the phone. Send a photograph of what you found and where, and we will tell you which animal you are dealing with — including when the answer is that it is one we do not handle.