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Rocky Mountain wood tick

Dermacentor andersoni

Also called wood tick

This tick can spread Rocky Mountain spotted fever, Colorado tick fever and tularemia, and rarely causes tick paralysis, so remove any attached tick right away and watch for fever, rash or weakness.

If you think you were bitten or stung, call Poison Help. Free, private, any hour.1-800-222-1222Call 911 for trouble breathing, swelling of the face or throat, or severe symptoms.

Photo: Toby, CC BY 4.0, via iNaturalist

SizeUnfed adult about 3 to 5 mm (1/8 to 1/5 inch); a fully fed female can reach about 13 to 16 mm (about 5/8 inch) long

Where in the houseBedroom, living room, outside near the house

WhenSpring and early summer, from snowmelt through about mid-July, with some activity again in fall; most tick paralysis cases occur April to June.

Check these features

Flat, oval to pear-shaped, brown to reddish-brown hard tick with 8 legs
Female has a silvery-gray to whitish mottled shield on the front of her back
Male has a spotted gray-and-white pattern across the back
Pale mottling also shows on parts of the legs and mouthparts
Fed females swell into a gray, bean- or pea-shaped body

Bites and stings

It attaches and feeds for days and the bite is often painless. An infected tick can pass on Colorado tick fever (flu-like fever, chills, headache and aches, usually 3 to 7 days after the bite), Rocky Mountain spotted fever (fever, headache, stomach upset, with a rash often a few days after the fever starts), or tularemia (fever with a sore at the bite and swollen glands). A tick left attached for several days can rarely cause tick paralysis: leg weakness or trouble walking that spreads upward over hours to days and can reach the breathing muscles; it usually improves once the tick is removed. Get medical care for fever, rash or flu-like illness in the weeks after a bite, and get emergency care for spreading weakness or any trouble breathing.

What to do

If a tick is attached, remove it right away; do not wait for a doctor. Use clean, fine-tipped tweezers (or a tick removal tool), grip the tick as close to the skin as you can, and pull straight up with slow, steady, even pressure. Do not twist, jerk or squeeze the body, and skip petroleum jelly, nail polish, heat or matches.
Wash the bite and your hands with soap and water, rubbing alcohol or hand sanitizer. Do not crush the tick with your fingers; seal it in a bag or container (note the date), wrap it tightly in tape, drop it in rubbing alcohol, or flush it. Then check the rest of your body, your children and your pets for more ticks.
If a person or pet has new weakness, unsteady walking or numbness that is spreading, search the scalp, hairline, neck and back carefully for an attached tick, remove it, and get medical care the same day.
Watch for fever, rash, headache or body aches over the next several weeks. If any appear, see a doctor and mention the tick bite, the date and where you likely picked it up; Rocky Mountain spotted fever needs early treatment.
For questions about a bite or a reaction, call Poison Help at 1-800-222-1222 (US, free, any hour). Call 911 for trouble breathing, swelling of the face or throat, or any severe symptoms.

Look-alikes

American dog tickThe two look nearly identical, with similar pale mottled shields, so location helps most: the Rocky Mountain wood tick lives in the Rocky Mountain and Intermountain West, while the American dog tick lives mostly east of the Rockies (Montana extension notes it in eastern Montana), and an expert may be needed where they overlap.

Western blacklegged tickThe western blacklegged tick is smaller, with black legs, a plain dark shield and no pale markings, while the Rocky Mountain wood tick has a silvery-gray mottled shield.

Blacklegged tick (deer tick)The blacklegged tick is smaller, has a plain dark shield with no silvery markings, and lives mainly in the eastern US.

Lone star tickA female lone star tick has one distinct white spot in the middle of her back rather than an all-over silvery mottled shield, and the species lives mainly in the eastern and southern US.

Brown dog tickThe brown dog tick is plain reddish-brown with no pale markings and often lives indoors where dogs are kept, while the Rocky Mountain wood tick is picked up outdoors in brush and grass.

Why it came inside

It does not live or breed indoors; it is carried in on people, dogs, clothing or gear after time in brushy, grassy or sagebrush areas. Ticks can drop off and later crawl onto someone in the house.

Keep it out

Use an EPA-registered insect repellent on skin or clothing, and consider permethrin-treated clothing and gear (follow the label).
Wear light-colored long sleeves and long pants tucked into socks in brush, tall grass or sagebrush, and walk in the middle of trails.
After coming inside, shower within two hours, check your whole body (including scalp, neck and behind the ears), and tumble-dry outdoor clothes on high heat.
Check dogs after outings and ask your vet about tick control products.
Keep grass mowed and clear brush and leaf litter around the house.

What helps

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Fine-tipped tweezers or tick remover

Grab the tick close to the skin and pull straight up with steady pressure.

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EPA-registered insect repellent

Look for an EPA-registered repellent with DEET, picaridin, IR3535 or oil of lemon eucalyptus, and follow the label, especially for children.

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Flea and tick prevention for pets

Ask your vet which product fits your pet. Never use a dog product on a cat.

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Hand lens

A 10x magnifier makes small features easier to check, like eye patterns, markings or the shield on a tick.

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