Only two types of ticks transmit Lyme disease in the United States: the blacklegged tick (commonly called the deer tick) and the western blacklegged tick. No other tick species, including the very common American dog tick or lone star tick, can spread the Lyme bacterium to humans. Knowing which tick bit you, and how long it was attached, makes a real difference in assessing your risk.
The Two Ticks That Carry Lyme
The blacklegged tick is widely distributed across the eastern United States and is responsible for the vast majority of Lyme disease cases in the country. It transmits two bacteria that cause Lyme: the well-known one found throughout the Northeast, Mid-Atlantic, and Upper Midwest, and a second species identified more recently in the Upper Midwest that can cause similar symptoms along with nausea and vomiting.
The western blacklegged tick fills the same role along the Pacific coast, particularly in northern California. It carries the primary Lyme bacterium but is associated with far fewer human cases each year, partly because its feeding behavior makes it less likely to bite people.
Together, these two species account for every confirmed case of Lyme disease acquired in the U.S. If you were bitten by a different type of tick, Lyme is not a concern (though other tick-borne illnesses could be).
How to Tell a Blacklegged Tick From a Dog Tick
The American dog tick is the tick most people encounter, and it’s often confused with the blacklegged tick. The differences are straightforward once you know what to look for.
Blacklegged ticks are smaller and darker. Males are dark brown to black and roughly the size and shape of a watermelon seed. Females have a distinctive two-tone look: a black shield just behind the head with a red-brown body behind it. Dog ticks are noticeably larger, and females have an off-white patterned shield behind the head against a dark brown body. That pale, ornate marking on the back is the easiest way to rule out a blacklegged tick.
Size matters most when it comes to nymphs, the juvenile stage of blacklegged ticks. Nymphs are less than 1/16th of an inch long, roughly the size of a poppy seed. They’re easy to miss entirely, which is why they’re responsible for a large share of Lyme transmissions. By the time a blacklegged tick reaches adulthood, it’s easier to spot, but nymphs can feed undetected for days.
When and Where the Risk Is Highest
Blacklegged tick nymphs are most active from late spring through summer, peaking in June and July. This overlaps with the time people spend the most time outdoors in shorts and sandals, which is why Lyme cases spike during those months. Adult blacklegged ticks are active in fall and even into winter on mild days, so the risk doesn’t disappear entirely when summer ends.
Geographically, the highest-risk areas are the Northeast (from Virginia up through Maine), the Upper Midwest (Minnesota and Wisconsin especially), and the mid-Atlantic states. On the West Coast, northern California carries the most risk from the western blacklegged tick. Blacklegged tick populations have been expanding their range in recent decades, so areas that were historically low-risk, including parts of the Southeast and southern Midwest, are seeing more cases.
How Transmission Actually Works
A tick carrying the Lyme bacterium doesn’t transmit it the moment it bites. The bacteria live in the tick’s gut and need time to migrate to the salivary glands before they can enter your bloodstream. In most cases, an infected tick must be attached for more than 24 hours before transmission occurs. This means finding and removing a tick the same day it attaches dramatically reduces your risk, even if the tick was carrying Lyme.
Not every blacklegged tick is infected. Infection rates vary by region and even by local habitat. In highly endemic areas of the Northeast, a substantial percentage of adult blacklegged ticks carry the bacterium, but in other parts of their range the rate is much lower. A tick bite from a blacklegged tick is not the same as a Lyme diagnosis.
Other Diseases From the Same Ticks
Blacklegged ticks don’t just carry Lyme. The same tick species transmits the bacteria that cause anaplasmosis, a different infection that produces fever, headache, and muscle pain. They also transmit babesiosis, a parasitic infection that attacks red blood cells, and a form of relapsing fever. In rare cases, a single tick bite can deliver more than one pathogen at once, leading to co-infections that can complicate diagnosis and treatment.
This is worth knowing because if you develop symptoms after a blacklegged tick bite but test negative for Lyme, one of these other infections could be the cause.
Removing a Tick Safely
If you find an attached tick, use clean fine-tipped tweezers to grasp it as close to the skin’s surface as possible. Pull straight up with steady, even pressure. Don’t twist or jerk, which can break off the mouthparts and leave them embedded. If you don’t have fine-tipped tweezers, regular tweezers or even your fingers work, as long as you grip close to the skin rather than squeezing the tick’s body.
Skip the home remedies. Petroleum jelly, nail polish, heat, and other folk methods don’t make ticks detach cleanly. They can actually agitate the tick and force infected fluid from its body into your skin, increasing your risk of infection rather than reducing it. After removal, clean the bite area with rubbing alcohol or soap and water, and save the tick in a sealed bag or container in case you develop symptoms later and want it identified.