Tick season generally runs from April through September in most of the United States, with the highest risk period falling between May and July. But the actual window depends heavily on where you live, what type of tick is common in your area, and how warm the winter was. In some regions, ticks can be active nearly year-round.
What Drives Tick Activity
Ticks don’t follow a calendar. They respond to temperature and humidity. Warm, humid conditions trigger their host-seeking behavior, the process where they climb to the tips of grass blades or low branches and wait for an animal or person to brush past. When conditions turn hot and dry, tick activity drops. Extended heat and drought in summer can actually kill off younger ticks and reduce populations the following spring.
The simplest rule: if the ground is thawed and the air temperature is above freezing, ticks can be active. That means even in northern states, a warm spell in February or March can bring ticks out. Snow cover and frozen ground keep them dormant, but the moment those conditions lift, the clock starts.
Peak Season in the Northeast and Midwest
The black-legged tick (commonly called the deer tick) is the primary carrier of Lyme disease, and it dominates the Northeast and upper Midwest. Adult deer ticks have a long active window. In Minnesota, researchers found adults active across an eight-month collection season, with the largest surge in April and a smaller, less consistent peak in October. They even showed sporadic activity during summer months.
The more dangerous period, though, is nymph season. Nymphal ticks are tiny, roughly the size of a poppy seed, and they’re responsible for the majority of Lyme disease cases in humans. In the Northeast, nymphal activity peaks in late May and June, with research pinpointing a peak around May 24th, give or take about six days depending on how warm the spring has been. This timing overlaps perfectly with when people start spending more time outdoors, which is a big part of why late spring and early summer carry the highest infection risk.
In the upper Midwest, nymphs are most active from May through August, with peak activity typically in June. Low-level nymphal activity can continue into October.
Peak Season in the South
The South has a different dominant species: the lone star tick, an aggressive biter found throughout the Southeast and south-central states. Adult lone star ticks are active from April through late August, and they actively seek out hosts rather than waiting passively like deer ticks. You’ll find them questing on tall grass in shaded areas or at the tips of low branches.
Milder winters in the South mean ticks can remain active much later into fall and emerge earlier in spring compared to northern states. Depending on how warm the winter is, some tick activity can persist nearly year-round in states like Georgia, Texas, and the Carolinas. The combination of warm temperatures and high humidity in the Southeast creates ideal conditions for tick survival across multiple seasons.
Peak Season on the West Coast
If you live in California or the Pacific Northwest, the timeline is flipped compared to the rest of the country. The western black-legged tick follows a winter-to-spring pattern rather than a spring-to-summer one. Adults become active in late November and are mostly gone by late April or early May. Younger ticks (nymphs and larvae) emerge in February and disappear by May or early June.
In central and southern California, this window is notably compressed. Researchers have described it as a “highly truncated” questing season compared to the longer activity periods seen in northwestern California, where Lyme disease is more established. If you’re hiking in coastal or inland California, your highest risk is during the cooler, wetter months, not during summer.
Why Nymphs Are the Biggest Threat
Adult ticks are easier to spot. They’re about the size of a sesame seed before feeding and large enough that most people notice them during a body check. Nymphs are a different story. At the size of a poppy seed, they can attach and feed for days without being detected, and that extended feeding time is what allows them to transmit pathogens.
The nymphal peak represents the maximum risk of human exposure to tick-borne diseases. In the Northeast and Midwest, that peak falls squarely in late May and June. In the South, nymphal lone star ticks overlap with adult activity from spring through summer. On the West Coast, nymphs are active from roughly February through May.
Winter Doesn’t Mean Zero Risk
A common assumption is that the first frost ends tick season. It doesn’t. Black-legged ticks in particular have a fall and winter active period. Even in the coldest parts of North America, deer ticks can be active on any day when the temperature rises above freezing and the ground isn’t covered in snow or frozen solid.
This means a December hike on a 40°F day with bare ground can still result in a tick encounter. The risk is lower than in June, but it isn’t zero. If you’re outdoors in winter and both conditions are met (unfrozen ground, above-freezing temperatures), it’s worth taking precautions.
Climate Is Shifting the Timeline
Warmer springs are pulling peak nymphal activity earlier in the year. Research on black-legged ticks has shown that the number of warm days accumulated through May directly predicts when the nymphal peak occurs. Warmer springs mean earlier peaks. This has practical consequences: the window when you need to be most vigilant is gradually starting sooner than it did a generation ago, and tick populations are expanding into northern areas that were previously too cold to support them year-round.
For most people in the continental U.S., the core message is straightforward. Your highest risk runs from April or May through July, with regional variations on either side. But if you’re outdoors in any month and the conditions are warm enough for you to be comfortable in a light jacket, they’re warm enough for ticks.