Quick answer
In the United States, Lyme disease is spread by two ticks: the blacklegged tick (also called the deer tick) in the Northeast, mid-Atlantic and upper Midwest, and the western blacklegged tick along the Pacific Coast. Not all ticks carry Lyme. CDC says lone star, American dog, Rocky Mountain wood and brown dog ticks cannot spread it.
- Lyme disease bacteria are spread by blacklegged ticks (Ixodes scapularis) and western blacklegged ticks (Ixodes pacificus).
- Most cases come from nymphs, which are about the size of a poppy seed and easy to miss. Adults are about the size of a sesame seed.
- The share of ticks carrying Lyme bacteria ranges from none to more than half, depending on the area and the tick’s life stage.
- Lone star, American dog, Rocky Mountain wood and brown dog ticks cannot transmit Lyme bacteria, but they can spread other diseases.
Pictures: what ticks that carry Lyme disease look like
The blacklegged tick goes through three life stages after hatching: larva, nymph and adult. The drawing below shows them side by side. Nymphs cause most Lyme infections, partly because they are so small that people often never notice the bite.
An unfed adult female blacklegged tick has an orange-red body around a dark shield (scutum) near the head. Nymphs are much smaller and harder to spot. A tick that has been feeding swells up and looks rounder, which can make it harder to recognize.
Which ticks carry Lyme disease?
| Tick | Where it lives (CDC) | Spreads Lyme? | Other illnesses it can spread |
|---|---|---|---|
| Blacklegged (deer) tick Ixodes scapularis | Widespread across the eastern U.S.; Lyme risk is highest in the Northeast, mid-Atlantic and upper Midwest | Yes | Anaplasmosis, babesiosis, Powassan virus disease, hard tick relapsing fever, one form of ehrlichiosis |
| Western blacklegged tick Ixodes pacificus | Pacific Coast, especially northern California | Yes | Anaplasmosis, hard tick relapsing fever |
| Lone star tick Amblyomma americanum | Northeast, South and Midwest | No | Ehrlichiosis, tularemia, Heartland and Bourbon viruses; linked to STARI rash and alpha-gal syndrome |
| American dog tick Dermacentor variabilis | East of the Rocky Mountains, with some areas farther west | No | Rocky Mountain spotted fever, tularemia |
For the full picture of where Lyme is most common, see our Lyme disease by state guide and the risk map.
The deer tick and Lyme disease
“Deer tick” is the everyday name for the blacklegged tick. Both nymphs and adult females can bite people, and CDC notes bite risk is highest in spring, summer and fall.
Timing follows the seasons. In eastern areas where Lyme is common, CDC says nymphs are most active from April through July, and adults are most active in early spring and fall. Adults can look for a host any winter day that stays above freezing.
A tick usually needs to stay attached for a while before it can pass Lyme bacteria to you. Read more in how long a tick needs to be attached.
Lone star and American dog ticks: do they carry Lyme?
No. CDC states that lone star ticks and American dog ticks cannot transmit Lyme disease bacteria. That does not make their bites harmless, though, since they can spread other infections.
- Lone star tick. Adult females have a single white dot on the back. CDC describes this tick as very aggressive toward people. Redness around a lone star bite does not always mean infection, because the tick’s saliva can be irritating.
- American dog tick. Adult females are the stage most likely to bite people, mostly in spring and summer.
What percentage of ticks carry Lyme disease?
There is no single number. CDC says the share of infected ticks ranges from none to more than 50 percent, depending on the region and the tick’s life stage. In most of the southeastern U.S., blacklegged ticks are almost never infected. Your state or local health department may publish tick testing data for your area.
The bottom line: not every tick carries Lyme, and not every bite from an infected tick causes infection. But because you cannot tell by looking, it makes sense to remove any tick promptly and watch for symptoms.
Found a tick? Remove it as soon as you can with fine-tipped tweezers, then watch for a rash or fever over the next several weeks. Our tick bite guide walks you through it.
We are collecting real experiences about finding ticks and tick bites from people who have lived it, shared with their permission. As stories come in, they will appear here, clearly marked as personal experience rather than medical advice.
To lower your chances of a bite in the first place, see our Lyme disease prevention guide.
Frequently asked questions
What ticks carry Lyme disease?
In the U.S., only the blacklegged (deer) tick and the western blacklegged tick spread Lyme disease bacteria to people.
Do all ticks carry Lyme disease?
No. Many tick species cannot spread Lyme at all, and even among blacklegged ticks, the share that carry the bacteria ranges from none to more than half depending on the area and life stage.
Do lone star ticks carry Lyme disease?
No. CDC says lone star ticks cannot transmit Lyme disease bacteria. They can spread other illnesses, such as ehrlichiosis, and are linked to alpha-gal syndrome.
Do American dog ticks carry Lyme disease?
No. CDC says American dog ticks cannot transmit Lyme bacteria. They can spread Rocky Mountain spotted fever and tularemia.
How many ticks carry Lyme disease?
It varies widely. CDC reports infection rates from 0 to over 50 percent depending on region and life stage, and blacklegged ticks in most of the Southeast are almost never infected.
Why are nymphs the biggest concern?
Nymphs are about the size of a poppy seed, so they are easy to miss and can stay attached long enough to spread infection. Adults are bigger and more likely to be found and removed.