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Western blacklegged tick

Ixodes pacificus

Also called western black-legged tick, western deer tick

This tick can spread Lyme disease and anaplasmosis, so remove any attached tick promptly and watch for a rash or fever over the next few weeks.

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: glmory, CC0, via iNaturalist

SizeUnfed adult female about 3 mm (1/8 inch); male about 2.5 mm (1/10 inch); nymph about 1 mm (1/25 inch, poppy-seed size); a fully fed female can swell to about 10 mm (3/8 inch) or more

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

WhenNymphs mostly in spring and early summer (peak mid to late spring in northern California); adults mostly from late fall through spring during cool, damp weather.

Check these features

Very small, flat, teardrop-shaped tick with 8 legs (adults and nymphs)
Adult female: reddish-orange rear body with a plain dark brownish-black shield covering the front half of the back
Dark brownish-black to black legs
No white, cream or silvery markings on the back
Male is smaller, oval and dark brownish-black all over; nymphs are tiny with a dark shield and a pale, see-through body

Bites and stings

It attaches and feeds for days, and the bite is often not noticed, especially from the tiny nymph. Most bites cause only a small red bump, but an infected tick can pass on Lyme disease or anaplasmosis. A Lyme rash usually spreads slowly and can show up about 3 to 32 days after a bite, often with fever, chills, headache or tiredness; anaplasmosis usually starts 1 to 2 weeks after a bite with fever, chills, bad headache and muscle aches. See a doctor if you get a rash, fever or flu-like illness in the weeks after a tick bite, and tell them when and where you were bitten.

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.
Watch for a rash, fever, chills, headache or body aches for the next several weeks. If any appear, see a doctor and mention the tick bite, the date and where you likely picked it up.
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.
For a tick found crawling but not attached, pick it up with tape or tweezers and seal it in a bag. Testing the tick is not recommended for medical decisions, so do not wait on test results if you feel sick.

Look-alikes

Blacklegged tick (deer tick, Ixodes scapularis)The two look almost the same and usually need a microscope to separate, so location is the practical clue: the western blacklegged tick lives in the Pacific Coast states and parts of Utah and Arizona, while the blacklegged tick lives in the eastern half of the US.

American dog tickThe American dog tick is larger and has a cream-colored shield with dark mottling, while the western blacklegged tick has a plain dark shield with no pale markings.

Lone star tickA female lone star tick has a single white spot on her back and long mouthparts, and the species lives mainly in the eastern and southern US; the western blacklegged tick has no white spot.

Brown dog tickThe brown dog tick is evenly reddish-brown, including its legs, and is often found indoors where dogs live, while the western blacklegged female has black legs and a two-tone dark shield over an orange-red body.

Rocky Mountain wood tickThe Rocky Mountain wood tick is bigger and has silvery-gray markings on its shield, while the western blacklegged tick is smaller with a plain dark shield and black legs.

Why it came inside

It does not live indoors; it rides in on people, pets, clothing or gear after time in woods, brush or grassy trail edges. Ticks that fall off can turn up on bedding, floors or furniture, and fed nymphs that drop off overnight are sometimes spotted on pillows.

Keep it out

Use an EPA-registered insect repellent on skin or clothing, and consider permethrin-treated clothing and gear (follow the label).
Wear long sleeves and long pants tucked into socks in wooded or brushy areas, and stay in the middle of trails.
After coming inside, shower within two hours, do a full-body tick check, and tumble-dry outdoor clothes on high heat to kill hidden ticks.
Check pets after time outdoors and ask your vet about tick control products.
Clear leaf litter and brush near the house and put a wood-chip or gravel strip between the lawn and wooded areas.

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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