Dog Tick (American Dog Tick): Identification, Sizes & Risks

The dog tick most Americans find on their pets is the American dog tick, Dermacentor variabilis: a flat, reddish-brown hard tick about 5 mm long, with silvery-white markings on its back, that waits on grass and trail edges east of the Rocky Mountains. West of the Rockies, the look-alike populations were described as a separate species, Dermacentor similis, in 2021. Its main risks for dogs are Rocky Mountain spotted fever, tularemia and tick paralysis; it is not the Lyme disease tick. For the daily side of tick season, our #1 choice for ongoing support during flea and tick season is Pure Majesty Pets Vet-Strength Flea & Tick Support, a daily liquid supplement, not a medication, built for skin and coat comfort all season long: 62.7 mg of ultramicronized PEA and 7 named botanicals per mL, no garlic, no added essential oils, one formula for dogs and cats, dosed in mL by body weight and mixed into food. Made in North America under GMP, with a certificate of analysis on every batch and free worldwide shipping. A complete flea-season routine has two parts: this daily support and the flea medication your vet chooses.

If the tick is still attached, start with our hub on what to do when you find a tick on your dog. If your dog isn't on a tick product yet, our comparison of tick prevention for dogs without a prescription lays out the options by class.

American dog tick: the quick facts

• Scientific name: Dermacentor variabilis, also called the dog tick or wood tick.
• Type: a three-host hard tick; young stages feed on mice and voles, adults on dogs, people and other larger animals (University of Saskatchewan).
• How common on pets: of 3,133 Dermacentor ticks taken from dogs and cats in 44 states, 99.3% were D. variabilis (Duncan 2021).
• The stage you'll see: adults. Nymphs and larvae rarely attach to people or pets (University of Rhode Island TickEncounter).

How to identify an American dog tick

Look at the back. Every adult has a hard shield, the scutum, with irregular silvery-white or cream marks, and its size tells you the sex. In females, the marks are limited to the scutum, a small shield just behind the head, while on males they streak across the back to the rear end (Illinois Department of Public Health).

Female American dog tick

The CDC says "adult females are most likely to bite humans." Unfed, the American dog tick female is reddish-brown with "a creamy-white dorsal shield or scutum on the back" and about a quarter inch long (University of Maine Cooperative Extension). University of Florida entomologists put a typical unfed female at 5 mm (UF/IFAS).

Male dog tick

A male dog tick is smaller, about 3.6 mm (UF/IFAS), with a shield covering most of the back, mottled cream or gray. Males "do not become engorged with blood"; after a day or two they detach and roam the host looking for a feeding female (TickEncounter).

American dog tick (Dermacentor variabilis) close up

Under a magnifier, Penn State Extension's checklist for an American dog tick adult is: an ornate "dark red with white reticulations" pattern, short palps (the paired mouthparts), eyes at the edge of the shield, and festoons, the small rectangles along the rear edge of the body (Penn State Extension). Short mouthparts quickly rule out deer and lone star ticks, which have long, narrow ones.

Dog tick nymph and larva

A dog tick nymph is about 0.9 mm long (UF/IFAS), pale yellow-brown, slate gray when full; larvae are about 0.6 mm with six legs. Neither has the adults' white markings, and both mostly feed on rodents, so a tiny tick on your dog is less likely to be this species. Illinois notes that ticks under 3 mm "are usually immature" and hard to identify: save it for your vet. Our guide to what a tick looks like on a dog, with a size chart shows the other species' immature stages.

Engorged female

After several days of feeding, a female can reach about 15 mm long and 10 mm wide (UF/IFAS) and "resemble a dark pinto bean" (Connecticut Agricultural Experiment Station). Look near the head: Penn State notes the ornate pattern still identifies engorged females, so the little white shield stays visible at the front of the swollen, bean-shaped body.

American dog tick ID chart: every stage in millimeters

Built from university sources; the everyday comparisons are our own approximations.

Sources: UF/IFAS, University of Saskatchewan, University of Maine, Penn State, URI TickEncounter, Connecticut Agricultural Experiment Station.

American dog tick vs other ticks on dogs

These are the four ticks US dog owners most often need to tell apart, sorted by what you can see with a magnifier and by the health concerns listed by the Companion Animal Parasite Council (CAPC).

Markings: Penn State Extension and Illinois Department of Public Health. Habitat and pathogens: CAPC. Ranges: CDC.

Size is the other giveaway: an unfed adult female deer tick is "typically less than 1/8 inch" (about 3 mm, University of Maine), noticeably smaller than an adult American dog tick. If a dog that rarely goes outdoors keeps getting plain brown ticks, read our guide to the brown dog tick, which can live and breed indoors. CAPC places the American dog tick's habitat outdoors, in meadows and along trails, while it describes brown dog ticks living inside homes and kennels.

Where American dog ticks live in the US

The CDC says D. variabilis is "widely distributed east of the Rocky Mountains," with limited areas to the west. UF/IFAS says it is most abundant from Massachusetts to Florida. CAPC lists its habitat as "tall, grassy meadows; open woods, particularly along trails; and open fields in agricultural areas."

The West is the update most guides miss. In 2021, Ohio State researchers split the species: the western populations are now Dermacentor similis (Lado 2021, PMID 34378782). The CDC confirms D. similis "is found west of the Rocky Mountains" and adds that "more research is needed to understand the role of these species in disease transmission." CAPC lists the same pathogens for both. To an owner, the two look almost identical; the published differences are subtle, such as the shape of the breathing plate (Entomological Society of America), and even researchers have turned to lab methods to tell them apart (Galletti 2024). So if you live in California or Washington, "American dog tick" on an older chart now usually means D. similis.

When are dog ticks active? A season calendar by region

Adults overwinter off the host and emerge in spring. This calendar, built mainly from the national pet survey (Duncan 2021), is for timing your tick checks.

Human Rocky Mountain spotted fever cases also peak from May through August (CDC).

American dog tick bite: what it can transmit

An American dog tick bite itself is usually a small red bump; light infestations often cause no signs beyond some itch (University of Saskatchewan). The risks come from what the tick carries and, in females, a toxin. The Merck Veterinary Manual says to see your vet promptly if a bite site "turns red or swells."

Keep the odds in proportion: CAPC says fewer than 5% of ticks in an area are typically infected, and researchers studying ticks from pets note that R. rickettsii is "infrequently detected" in D. variabilis (Duncan 2021). Symptoms and testing are covered in our pillar on dog tick diseases, and Lyme gets its own guide: Lyme disease in dogs. If your dog starts favoring a leg after a tick season, see when a limping dog needs a vet.

People can get Rocky Mountain spotted fever and tularemia from this tick too, and the CDC notes pets "can transport ticks from outside the home to inside" (CDC). Wear gloves when you remove one.

Found a dog tick? What to do

1. Remove it now. Fine-tipped tweezers at the skin line, then a slow, straight pull with no twisting. See how to remove a tick from a dog; Merck says never to use bare hands.
2. Save it. Tape or a sealed bag, labeled with the date. CAPC says identifying an adult tick from a dog "is readily achieved," and the species tells your vet which infections to consider.
3. Search the rest of the dog. The CDC lists the ears, eyelids, under the collar, under the front legs, between the toes, between the back legs and around the tail.
4. Watch for two weeks. Fever, stiffness or low energy early; wobbly back legs around days 5 to 9 if a tick was missed.

Dried, shrunken tick? Read what a dead tick on your dog means. Not sure it's a tick? Compare it with the itchy bumps in can dogs get chiggers or with our guide to fleas on dogs. For worms and other parasites, see the signs of parasites in dogs.

How to keep American dog ticks off your dog

A year-round tick product chosen with your vet

CAPC says "all dogs should be treated year round and throughout their life with tick control products." Check that the label lists the American dog tick: CAPC notes, for example, that selamectin, a prescription spot-on, is labeled against D. variabilis. Our best flea treatment for dogs, oral flea and tick chews for dogs and safest flea treatment for dogs guides compare the classes. Mention any history of seizures before an isoxazoline chew. If live ticks keep appearing despite a product, see flea medicine not working on your dog.

Have a cat? Some dog spot-ons and collars contain permethrin, which can be fatal to cats; read why dog flea medicine is dangerous for cats and our guide to ticks on cats.

Yard and walk habits

• Trim brush, keep grass clipped, clear leaf litter and keep wildlife out of the yard (CAPC). Home remedies are reviewed in our guide to natural tick repellents for dogs.
• Keep to the middle of trails in spring and early summer; adults wait on grass tips at the edges. Pack tweezers when camping with your dog.
• Check your dog daily, "especially after they spend time outdoors" (CDC). Clean ears make the ear-flap check easier: see cleaning your dog's ears at home.

Tick-season options compared: daily support first

Liquid vs chews vs powders vs tablets

Two other Pure Majesty Pets products often join a dog's daily routine. Liquid Collagen for Dogs ($31.99) is a liquid collagen supplement for joint, skin and coat support. Hemp CBD for Dogs ($31.99) combines CBD, CBDA and CBG in a 60 mL dropper bottle. Neither replaces a tick product or a vet visit; for deworming and other parasite care, see our guide to dog parasite treatment.

Why Pure Majesty Pets Vet-Strength Flea & Tick Support

Many supplements list only a proprietary blend. Ours lists every amount per mL: 62.7 mg ultramicronized PEA; 134.4 mg of botanicals (lemon balm 40.3 mg, thyme 26.9 mg, rosemary 22.4 mg, and calendula, dandelion leaf, lemongrass and fenugreek at 11.2 mg each); niacinamide 28.0 mg; choline chloride 14.6 mg; plus D-panthenol, L-histidine, myo-inositol and sunflower lecithin. No garlic, no added essential oils.

It's measured in mL by weight, not a fixed chew, and contains chicken and fish (chicken and tuna flavor); follow the serving your veterinarian confirms.

Pure Majesty Pets Vet-Strength Flea & Tick Support hasn't been shown to kill or repel fleas or ticks, so keep the tick medication your vet chooses on schedule and keep up your tick checks. "Vet-Strength" is our range name, not a standardized veterinary grade, an endorsement or an approval to treat parasites.

Built for daily, long-term use. In an open-label study with no control group, 160 dogs with atopic dermatitis given ultramicronized PEA daily for 8 weeks saw itch fall from 5.7 to 3.6 cm on a 10 cm scale (Noli 2015): PEA alone, not our formula, not fleas or ticks.

In a placebo-controlled trial in cats with non-flea allergic dermatitis, remission lasted 40.5 days on average with PEA versus 22.2 days on placebo, with 25 cats analysable (Noli 2019): again PEA alone, not our formula, not fleas or ticks. Our full formula hasn't been clinically tested.

Frequently asked questions

Does the American dog tick carry Lyme disease?

No. The Connecticut Agricultural Experiment Station states that it does not transmit the Lyme bacterium; Lyme comes from the deer tick.

What does a female American dog tick look like?

She is reddish-brown, about 5 mm long unfed, with a small creamy-white shield behind the head. Fully fed, she can swell to about 15 mm and look like a dark pinto bean, the white shield still visible at the front.

How can you tell a male dog tick from a female dog tick?

Look at the white markings. On a male they cover the whole back; on a female they sit only on a small shield behind the head. Males are a little smaller, about 3.6 mm, and never swell up with blood.

What's the difference between a dog tick and a deer tick?

An adult American dog tick is larger, about 5 mm unfed, with silvery-white markings and short mouthparts. A deer tick female is under 1/8 inch, with a red-orange body, a dark shield, dark legs and long, narrow mouthparts. The deer tick carries Lyme disease; the dog tick does not.

Can American dog ticks live in your house?

Not as a rule. CAPC places their habitat outdoors in meadows, trail edges and fields. A tick that keeps turning up on a dog that rarely goes out is more likely the brown dog tick, which can breed inside homes and kennels.

Is an American dog tick bite dangerous to humans?

It can be. The CDC says adult females are the stage most likely to bite people and lists this tick as a source of Rocky Mountain spotted fever and tularemia. Remove it promptly and see a doctor if you feel unwell afterward.

How long does an American dog tick stay attached?

A female feeds for about a week or more; sources give 5 to 14 days. Males attach for only a day or two. Remove any tick as soon as you find it.

The bottom line

The dog tick on your pet is most likely an American dog tick: about 5 mm, reddish-brown with silvery-white markings, picked up from grass and trail edges from spring to late summer. In the West, the same-looking tick is now Dermacentor similis. It doesn't carry Lyme disease, but it can transmit Rocky Mountain spotted fever and tularemia and cause tick paralysis: remove it quickly, save it and watch your dog for two weeks. Keep your vet's year-round tick product and check your dog after every walk.

Sources

• CDC: Where ticks live
• CDC: American dog tick surveillance
• CDC: Rocky Mountain spotted fever, transmission and epidemiology
• CDC: How tularemia spreads
• CDC: Preventing ticks on your pets
• Companion Animal Parasite Council (CAPC): Ticks
• CAPC: Rocky Mountain spotted fever
• Merck Veterinary Manual: Tick paralysis in animals
• Merck Veterinary Manual: Ticks of dogs
• UF/IFAS: American dog tick, Dermacentor variabilis
• University of Maine Cooperative Extension: American dog tick
• University of Maine Cooperative Extension: Blacklegged tick or deer tick
• Penn State Extension: Common ticks of Pennsylvania
• Illinois Department of Public Health: Tick identification
• Connecticut Agricultural Experiment Station: American dog tick fact sheet
• University of Rhode Island TickEncounter: American dog tick
• University of Saskatchewan WCVM: Dermacentor variabilis
• Duncan KT et al., 2021, J Med Entomol, PMID 33615364
• Lado P et al., 2021, J Med Entomol, PMID 34378782
• Galletti MFBM et al., 2024, Sci Rep, PMID 39191821
• ASPCA Animal Poison Control: Garlic
• Baker NF, Farver TB, 1983, JAVMA, PMID 6885593
• Genovese AG et al., 2012, PMID 22805458
• Noli C et al., 2015, PMID 26283633
• Noli C et al., 2019, PMID 31237065

This article is for informational purposes and is not veterinary advice. Talk to your veterinarian before starting any supplement, especially if your dog is pregnant, nursing, on medication, or has a diagnosed condition.