Ticks in Washington State

Are there ticks in Washington state?

Yes — and the more useful answer is how many, and which, and when.

Washington has ticks, and it does not have anything resembling the tick problem of New England, the mid-Atlantic or the upper Midwest. Both halves of that sentence matter. People who move here from the east coast often arrive assuming tick checks after every walk, and people who have lived here all their lives often assume ticks are something that happens in other states. Neither is quite right.

The best regional data we have is a six-year surveillance program run by the Washington State Department of Health and published in the CDC’s journal Emerging Infectious Diseases in 2020. Between 2011 and 2016 that work collected 977 unfed, host-seeking ticks from 53 sites across 19 counties, and tested them. That is the backbone of this page, because it is the only thing anybody has that describes ticks in this state rather than ticks in general.

What it found, in one paragraph: six species, dominated by the western black-legged tick; a Lyme infection rate in those ticks of around 4%; a strong spring peak with almost no summer activity; and 202 human tick-borne disease cases over six years, of which 68 were acquired inside Washington. That is a real risk and a small one, and it behaves differently here than the national coverage would lead you to expect.

The ticks that actually live here

Six species turned up in that surveillance, and they were not evenly distributed.

• Western black-legged tick (Ixodes pacificus) — 438 collected, by far the most common, and the species that matters most for disease.
• Ixodes spinipalpis — 236. Mainly a tick of rodents and rabbits rather than of people.
• Ixodes angustus — 99. Another small-mammal specialist.
• Rocky Mountain wood tick (Dermacentor andersoni) — 151.
• American dog tick (Dermacentor variabilis) — 46. The Department of Health calls this one the western dog tick, which is the name used on our own species page; they are the same animal.
• Ixodes auritulus — 5. A bird tick, and not a human-biting concern.

The Department of Health’s public guidance refers to four tick species commonly found in Washington that bite people and can transmit disease, which fits: the western black-legged tick, the two Dermacentor wood ticks, and the soft ticks dealt with further down. The remaining Ixodes species in the surveillance list are animals of rodent burrows and bird nests, and most people will never encounter one.

The practical shortlist is shorter still. If a tick bites you in Washington, it is overwhelmingly likely to be either a western black-legged tick or one of the two wood ticks.

Western black-legged tick, the one that carries Lyme

Small, dark, and the only Washington tick that regularly matters for Lyme disease.

This is the Pacific coast counterpart of the deer tick that the eastern Lyme literature is written about. It is a small tick — an unfed adult female is around the size of a sesame seed, with a dark body and reddish-brown abdomen, and the nymphs are far smaller than that. It lives in shaded, humid habitat: wooded edges, brush, tall grass against treelines, leaf litter.

In the state surveillance, 4.0% of western black-legged ticks tested carried Borrelia burgdorferi sensu stricto, the Lyme bacterium. Related findings in the same ticks: 3.8% carried B. burgdorferi sensu lato, 4.4% carried B. miyamotoi, which causes a relapsing-fever-type illness, and 1.9% carried Anaplasma phagocytophilum, which causes anaplasmosis.

Those percentages are the thing to hold onto, because they are much lower than the figures quoted in eastern Lyme reporting, where infection rates in nymphal deer ticks in some counties run many times higher. A bite here is not nothing. It is also, statistically, very unlikely to transmit anything.

Infection rates were not uniform across the state. The highest rate of B. burgdorferi sensu stricto was found in Clallam County, on the Olympic Peninsula, at 9.1%. There is a profile of this species in the library at western black-legged tick.

Rocky Mountain wood tick and American dog tick

Bigger, browner, and a different set of concerns.

The two Dermacentor ticks are the ones most people picture: larger than an Ixodes tick, brown with pale or mottled markings on the shield behind the head, and much more noticeable on skin or on a dog. The Rocky Mountain wood tick is the more common of the two in Washington by about three to one in the surveillance data.

Both are competent vectors of Rickettsia rickettsii, which causes Rocky Mountain spotted fever, and of Francisella tularensis, which causes tularemia. Two points of reassurance on that. First, the surveillance did not detect either organism in any of the Dermacentor ticks tested. Second, Rocky Mountain spotted fever is genuinely rare here: two probable cases over the six-year period, both with likely exposure in north central Washington.

These ticks are also the ones associated with tick paralysis, which the Department of Health lists among the conditions acquired in Washington. It is rare, it is caused by a toxin in tick saliva rather than by an infection, and it resolves when the tick is removed — which is one more reason to look properly rather than to assume.

Soft ticks, cabins, and relapsing fever

The Washington tick problem that is most specific to this state, and the one fewest people know about.

Soft ticks are a different family altogether. The Department of Health describes them as living in mountainous regions, particularly in rodent nests and cabins in eastern Washington, and emerging at night to feed briefly rather than attaching for days. Most people bitten never see the tick.

They transmit tick-borne relapsing fever, and in the surveillance period that was tied with tularemia as the most reported tick-borne illness among Washington residents — 25 cases each. Every relapsing fever case had exposure in eastern Washington, mostly in Okanogan and Spokane counties, and the classic scenario is a night spent in a rustic cabin with a rodent problem in the walls or the crawlspace.

Which makes it, unusually, a pest control question as much as a medical one. A cabin with rodents in it is the precondition. Dealing with the rodents is covered under rodent control and exclusion and repairs, and for a holiday cabin that sits empty most of the year, exclusion is the only thing that works at all.

Is the lone star tick in Washington?

No, not as an established population — and the question is asked often enough to deserve a direct answer.

The lone star tick is an eastern and southeastern species. It is expanding its range northward, which is why it appears in a great deal of recent news coverage, and it is associated with alpha-gal syndrome, the red meat allergy that follows some lone star bites. None of that currently describes Washington.

What can happen is a single tick arriving on a person, a dog, a horse or a load of hay from somewhere it does live. That is precisely why the Department of Health runs an identification service — you remove the tick, put it in a crush-proof container, submit it through their online form, and they email you the species and what it can carry. If a lone star tick ever does establish here, that is the system that will notice.

The same answer applies to several other ticks people ask about. The eastern black-legged tick, the Gulf Coast tick and the Asian longhorned tick are not Washington animals.

Ticks in western Washington versus eastern Washington

The split is real, but it does not run the way most people assume.

The common assumption is that ticks are a dry-side problem — eastern Washington, sagebrush, hot summers. That is partly true and it is not the whole picture.

Western Washington has the western black-legged tick, and the single highest Lyme infection rate in the state surveillance came from Clallam County, which is about as far west as it is possible to get. Shaded, humid, brushy habitat suits Ixodes ticks, and the west side has a great deal of that.

Eastern Washington is where the relapsing fever picture sits — all 25 cases in the surveillance period had eastern exposure — and where the Dermacentor wood ticks are most associated with open country, trails and hunting.

For Whatcom and Skagit counties specifically, the realistic exposure is the western black-legged tick along brushy trail edges, in second-growth woodland, and in the transition between pasture and treeline. Not lawns, not gardens, and very rarely houses.

When tick season actually is here

Spring, and it is the single most useful fact on this page.

In the state surveillance, about 91% of the three primary vector species were collected between March and May, and nearly all of them were adults. That is a sharp, early peak. By the time people are thinking about ticks — July and August, when the hiking is best — the main activity window has largely closed.

One caveat on that figure, because it is easy to over-read. Those drags ran March to October, so the study was not looking for ticks in December or January and the 91% describes the shape of the sampled season rather than the whole year. Adults of the western black-legged tick are active through the cool months, which in a climate with no hard freeze means a mild bright day in February is squarely within their season. The species page on the western black-legged tick goes through the life stages properly.

The practical version: the checks that matter most happen earlier than people expect, a tick found in February is not a mistake, and the summer-vigilance habit absorbed from national coverage is aimed at the wrong months here. The seasonal picture for everything else is in the Whatcom County pest year.

How much Lyme disease there actually is in Washington

Less than almost anybody assumes, and still not zero.

Over 2011 to 2016 there were 202 tick-borne disease cases reported among Washington residents, and 68 of those — about a third — were acquired inside the state. The rest were acquired while traveling, which is a meaningful share and says something about how Washingtonians encounter ticks.

Within that, 16 Lyme cases had exposure in Washington, spread across 12 counties. Tularemia and tick-borne relapsing fever each accounted for 25 cases. Rocky Mountain spotted fever accounted for two probable cases.

The honest reading of those numbers is that tick-borne illness in Washington is genuinely uncommon, that it is not evenly spread, and that the dominant risks are not the ones in the national headlines. It is also a small dataset over six years, which is a reason to treat a bite seriously rather than a reason to dismiss one.

The Lyme question specifically — what the symptoms are, how often the bull’s-eye rash appears, and why a Whatcom County bite is not the same probabilistic event as a Connecticut one — is covered at length on the western black-legged tick page rather than repeated here.

Nothing on this page is medical advice. If you have been bitten and you feel unwell, that is a conversation for a doctor, and the Department of Health’s guidance is to mention the bite explicitly.

What to do about ticks on a property

Habitat, mostly, and less than the internet would like to sell you.

Ticks need humidity and shade. They sit on vegetation at the height of a passing animal and wait. So the things that reduce encounters on your own ground are unglamorous and mostly free:

• Keep lawn short where people and dogs actually spend time.
• Pull leaf litter, long grass and brush back from paths, play areas and the edge of the mown part of a yard.
• Keep woodpiles off the ground and away from the places children play, which also deals with the rodents that carry immature ticks.
• Accept that the brushy edge of a property is tick habitat, and treat it as somewhere to walk through rather than sit in.
• Check dogs after walks. Dogs bring ticks indoors far more often than people do, which is why this page sits alongside flea control rather than alongside anything structural.

Broadcast acaricide treatment of a whole yard is a real practice in high-density tick regions. In a county with this tick load, it is not a proportionate response, and we would not propose it.

What we do and do not do about ticks

We do not treat for ticks, and this page exists anyway.

Tick work is not on our confirmed service list. That is a deliberate position rather than an oversight: there is no honest case for selling a yard tick program in Whatcom County at the exposure levels the state’s own surveillance describes, and a service page for something we do not do would be the same dishonesty as a pest library full of species that do not live here.

What we do is the thing underneath several of the tick questions people actually ask. A cabin with rodents in the walls is the setting for relapsing fever, and rodents in walls is our work. A dog bringing things into a house is usually a flea question before it is a tick question, and fleas are our work. Yard habitat around a building is part of what we look at on any exterior job.

And when somebody rings about a tick, the answer is the Department of Health’s identification service and a doctor if they feel unwell — not a visit from us. We would rather be the page that told you that than the company that sold you a treatment for it.