Only blacklegged ticks (also called deer ticks) transmit Lyme disease in the United States. Two species are responsible: the blacklegged tick, found across the eastern half of the country, and the western blacklegged tick, found along the Pacific coast, particularly in northern California. No other tick species, including the common dog tick or the Lone Star tick, can give you Lyme disease.
The Two Tick Species That Carry Lyme
The blacklegged tick is the primary carrier in the Northeast, Upper Midwest, and Southeast. Its close relative, the western blacklegged tick, fills the same role on the West Coast. Both species transmit the same bacterium, though Lyme cases are far more concentrated in the eastern U.S. where blacklegged tick populations are densest.
In the U.S., Lyme disease is caused by the bacterium Borrelia burgdorferi and, rarely, a second species called Borrelia mayonii. The tick picks up these bacteria by feeding on infected animals like white-footed mice or other small mammals, then passes the bacteria to the next host it bites, which can be you.
How to Identify a Blacklegged Tick
Blacklegged ticks get their name from their distinctly dark legs. Adults are about the size of a sesame seed, flat, oval-shaped, and dark reddish-brown. After feeding, they swell into a rounder shape and their body appears darker. They look noticeably different from dog ticks, which are larger, have a lighter brown body, and often feature white or gray markings on their back.
Nymphs, the juvenile stage, are much harder to spot. They look almost identical to a poppy seed in both size and color. This is a critical detail, because nymphs are actually the life stage most likely to give you Lyme disease. Their tiny size makes them easy to miss on your skin, so they tend to stay attached longer without being noticed.
Why Nymphs Are the Biggest Threat
Both adult and nymphal blacklegged ticks can transmit Lyme, but nymphs pose a particularly high risk for two reasons. First, they’re abundant, far outnumbering adults in most environments. Second, at the size of a poppy seed, they can feed on you for days without detection. Most people who develop Lyme disease never noticed a tick bite at all, and nymphs are usually the reason. Adults are small too, but at sesame-seed size, they’re at least visible during a careful body check.
Larvae, the earliest life stage, are even tinier but generally haven’t yet picked up the Lyme bacterium from an infected host. They pose minimal risk.
When These Ticks Are Most Active
The timing of tick activity depends heavily on where you live, and it spans more of the year than many people realize.
In the Northeast and Upper Midwest, nymphs are most active from May through July, which lines up with the peak season for Lyme disease diagnoses. Adults have a bimodal pattern, with activity surging in fall (October to November) and again in spring (April to May). That means adult ticks are actively seeking hosts even in cooler months when many people assume tick season is over.
In the Southeast, larvae and nymphs are active together from spring through early summer, roughly April to July. Adults stay active continuously from fall through winter and into spring, peaking between November and March.
Along the Pacific coast, the pattern is similar to the Southeast, with nymphs peaking in spring (April to June) and adults active from fall through winter. In practical terms, there is no month of the year in much of the U.S. where blacklegged tick exposure is impossible.
Where These Ticks Live
Blacklegged ticks are widely distributed across the eastern United States, from Maine down through the Southeast and across the Upper Midwest. Western blacklegged ticks are concentrated along the Pacific coast, with northern California being a particular hotspot.
Both species thrive in wooded, brushy, and humid environments. Leaf litter on the forest floor, tall grasses at the edges of wooded areas, and overgrown trails are classic habitats. You don’t need to be deep in the wilderness to encounter them. Backyards that border wooded areas, gardens with ground cover, and even well-maintained parks with adjacent brush can harbor ticks. They wait on low vegetation and latch onto hosts that brush past.
How Transmission Actually Works
A tick doesn’t transmit Lyme the moment it bites. The bacterium lives in the tick’s gut, and it takes time for the pathogen to migrate to the tick’s salivary glands and enter your bloodstream. Most estimates suggest a tick needs to be attached for roughly 36 to 48 hours before transmission occurs, though this window isn’t absolute. The practical takeaway: finding and removing a tick within a day of attachment significantly reduces your risk.
This is another reason nymphs are so dangerous. An adult tick feeding on your thigh or behind your ear might get spotted in the shower that evening. A poppy-seed-sized nymph tucked into your scalp, waistband, or behind your knee can easily feed undetected for two or three days.
Ticks That Don’t Transmit Lyme
Several other common tick species bite humans but cannot give you Lyme disease. The American dog tick is widespread across the eastern U.S. and is the one most people picture when they think of ticks. It’s larger and lighter-colored than the blacklegged tick and does not carry Borrelia burgdorferi. The Lone Star tick, recognizable by the white dot on the female’s back, is aggressive and common in the Southeast and mid-Atlantic, but it also does not transmit Lyme.
These other species do carry different pathogens that can cause illnesses with some overlapping symptoms, like Rocky Mountain spotted fever or ehrlichiosis. If you develop a fever, rash, or flu-like symptoms after any tick bite, the species matters for diagnosis and treatment. Saving the tick in a sealed bag or taking a clear photo can help your doctor identify it.
Reducing Your Risk
Since only blacklegged ticks transmit Lyme and they need extended feeding time to do it, your best protection is preventing bites and catching attached ticks early. Wearing long pants tucked into socks in brushy areas, using insect repellent on exposed skin, and treating clothing with permethrin all reduce the chance a tick reaches your skin.
After spending time outdoors in tick habitat, do a thorough body check. Pay special attention to hidden spots: behind the ears, along the hairline, under the arms, around the waistband, behind the knees, and between the toes. Showering within two hours of coming indoors has been associated with lower tick-borne illness rates, likely because it dislodges unattached ticks and provides an opportunity to spot attached ones. Tossing clothes in a hot dryer for 10 minutes kills ticks that may have hitched a ride.
If you find an attached tick, remove it with fine-tipped tweezers by grasping it as close to the skin as possible and pulling straight up with steady pressure. Avoid twisting, crushing, or using heat or petroleum jelly, all of which can cause the tick to release more saliva into the bite site.