Only blacklegged ticks spread Lyme disease in North America

Not all ticks carry Lyme disease — only blacklegged ticks (also called deer ticks) transmit the bacteria that causes it. Other common tick species, like lone star ticks and American dog ticks, do not carry Lyme disease, though they can spread other illnesses. Blacklegged ticks are found across the eastern United States, parts of the upper Midwest, and the Pacific Coast, with the highest concentration in the Northeast and upper Midwest.

The tick must be infected with the bacterium Borrelia burgdorferi to pass Lyme disease to you. Not every blacklegged tick carries this bacterium — infection rates vary by region and season. In some areas, fewer than 10 percent of blacklegged ticks are infected; in others, the rate is higher. Even if you are bitten by an infected tick, transmission does not happen immediately. The tick typically needs to be attached for 24 to 48 hours before the bacteria enters your bloodstream.

Key Takeaways

  • Blacklegged ticks are the only tick species in North America that spreads Lyme disease, and they are smaller than other common ticks.
  • An infected blacklegged tick must stay attached to your skin for roughly 24 to 48 hours to transmit Lyme disease bacteria.
  • Blacklegged ticks are most active in spring and fall, though they can bite year-round in milder climates.
  • Removing a tick within 24 hours of attachment significantly reduces your risk of infection, even if the tick is infected.

How to recognize a blacklegged tick

Blacklegged ticks are much smaller than other tick species, which makes them easy to miss. An adult blacklegged tick is about the size of a sesame seed — roughly 3 to 4 millimeters long. The nymphs (young ticks) are even tinier, about the size of a poppy seed, and are responsible for most Lyme disease cases because they are so hard to spot and remove.

Adult blacklegged ticks have a dark brown or black body with reddish-brown legs, which is how they got their name. The body is oval and flat before feeding, then becomes rounder and larger as it fills with blood. Nymphs are tan or light brown and nearly invisible on skin. If you find a tick on your body, look for the dark coloring and small size — these features distinguish blacklegged ticks from the larger, brown American dog tick or the distinctive white-marked lone star tick.

Where blacklegged ticks live and when they are most active

Blacklegged ticks live in wooded areas, tall grass, and leaf litter where they wait for animals or humans to pass by. They do not jump or fly — they climb onto your clothing or skin when you brush against vegetation. Ticks are most active in spring (April through June) and fall (September through November), when temperatures are mild and humidity is high. However, in warmer regions, blacklegged ticks can remain active throughout the year.

The nymph stage, which occurs in late spring and early summer, is when most human Lyme disease infections happen. Nymphs are feeding during this time and are so small that people often do not notice them. Adult ticks are more visible but are active primarily in fall and early winter. If you spend time outdoors in tick habitat during these seasons, checking your body and clothing for ticks becomes especially important.

Geographic distribution of blacklegged ticks

Blacklegged ticks are found across much of the United States, but they are concentrated in certain regions. The Northeast — from Maine through Pennsylvania and into the upper Midwest — has the highest density of blacklegged ticks and the highest rates of Lyme disease. They are also established along the Pacific Coast, particularly in California, Oregon, and Washington. In recent decades, the range of blacklegged ticks has expanded northward and westward, so they are now found in areas where they were uncommon 20 years ago.

If you live in or travel to a region where blacklegged ticks are present, the risk of encountering an infected tick is real but not certain. Local health departments and the Centers for Disease Control and Prevention (CDC) maintain maps showing where blacklegged ticks have been found. Checking whether blacklegged ticks are established in your area can help you decide how carefully to check for ticks after outdoor activities.

What to do if you find a tick on your skin

If you discover a tick attached to your skin, remove it promptly using fine-tipped tweezers. Grasp the tick as close to the skin as possible and pull straight upward with steady pressure. Do not twist, jerk, or squeeze the tick's body — this can cause the tick to release bacteria into your skin. After removal, place the tick in a sealed bag or container and wash the bite area with soap and water.

Removing a tick within 24 hours significantly reduces the risk of Lyme disease transmission, even if the tick is infected. Some people save the tick in a freezer or sealed container so they can show it to a doctor if symptoms develop later. If you are unsure whether the tick is a blacklegged tick, a photo sent to your local health department can help identify it. Do not use petroleum jelly, nail polish, or heat to remove a tick — these methods do not work and may cause harm.

Reducing your risk of blacklegged tick bites

The most effective way to prevent Lyme disease is to avoid tick bites in the first place. When spending time outdoors in wooded areas or tall grass, wear light-colored clothing so ticks are easier to spot. Tuck your pants into your socks and your shirt into your pants to create a barrier. Use an insect repellent containing 20 percent DEET on exposed skin, or treat your clothing with permethrin before going outside — permethrin kills ticks on contact and remains effective through several washings.

After spending time outdoors, check your entire body for ticks, paying special attention to warm, moist areas like the groin, armpits, and behind the knees. Nymphs are so small that a careful visual inspection is essential. Shower within two hours of coming indoors and put your clothes in the dryer on high heat for at least 10 minutes to kill any ticks that may be hiding in fabric. These steps do not may provide you will never encounter a blacklegged tick, but they significantly lower your risk.

Frequently Asked Questions

Can you get Lyme disease from a tick that is not attached to your skin?

No. A tick must be attached and feeding to transmit Lyme disease. If you find a tick crawling on your clothing or skin but not yet attached, you can brush it off or remove it without risk of infection. The bacteria lives in the tick's gut and enters your bloodstream only through the feeding process.

What should I do if I cannot remove the entire tick?

If the tick's head or mouthparts break off and remain in your skin, do not panic. The head alone cannot transmit Lyme disease. Wash the area with soap and water and let it heal. If the area becomes infected or you develop a rash, contact your doctor. Most of the time, the remaining parts will work out of the skin on their own.

Are all blacklegged ticks infected with Lyme disease?

No. The percentage of blacklegged ticks carrying the Lyme disease bacterium varies by location and season, ranging from less than 10 percent to over 50 percent in some areas. Even if you are bitten by an infected tick, you do not automatically develop Lyme disease — removal within 24 hours usually prevents transmission.

Can I get Lyme disease in winter?

In most of the United States, blacklegged ticks are less active in winter and the risk is lower. However, in milder climates or during unusually warm winter days, ticks can remain active. If you spend time outdoors in winter in a region where blacklegged ticks are present, checking for ticks is still worthwhile.

Do I need to see a doctor after a blacklegged tick bite?

Not necessarily. If you remove the tick within 24 hours, your risk of infection is very low. However, if you develop a rash, fever, joint pain, or fatigue within three to 30 days of the bite, contact your doctor and mention the tick exposure. Early treatment with antibiotics is highly effective.