Mosquito season is the stretch of warm, humid months when mosquitoes are actively breeding, biting, and buzzing around your yard. In most of the U.S., it runs roughly from April through September, but the exact window depends heavily on where you live. Some southern regions deal with mosquitoes nearly year-round, while northern states may only see a few intense months of activity.
What Triggers Mosquito Season
Mosquitoes are cold-blooded, so temperature dictates nearly everything about their life cycle. They become inactive below 50°F (10°C). Once temperatures consistently stay between 60°F and 80°F with moderate to high humidity, conditions are ideal for breeding and feeding. The sweet spot for peak activity is around 70°F.
But the spring kickoff isn’t just about air temperature. Mosquitoes survive winter in different forms depending on the species. Some overwinter as eggs buried in soil or leaf litter, waiting for rising water tables and warming water temperatures to trigger hatching in spring. Others survive as mated females tucked into sheltered spaces like hollow logs, basements, or storm drains, emerging when nighttime temperatures climb high enough for them to start seeking blood meals and laying eggs. A third group spends winter as larvae burrowed into sediment at the bottom of standing water, resuming growth as soon as the water warms.
This is why mosquito season doesn’t flip on like a switch. It builds gradually as each of these overwintering strategies plays out on its own timeline, with successive waves of different species appearing through spring and into summer.
When Mosquito Season Starts by Region
Geography makes a dramatic difference. Here’s a general breakdown across the U.S.:
- Gulf Coast, Florida, and Hawaii: February through November, with some areas experiencing mosquito activity year-round.
- The South and inland Southwest: March through September.
- Mid-Atlantic, Great Lakes, and Northern West: April through September.
- New England, Northern Midwest, and Pacific Northwest: May through September.
- Interior West at higher elevations: June through September, the shortest window due to cooler mountain temperatures.
These are averages. A warm, wet spring can push the start earlier by a few weeks, while a dry spell can delay breeding even when temperatures are right. Mosquitoes need standing water to lay eggs, so rainfall patterns matter as much as heat.
Peak Season and When Biting Is Worst
Across most of the country, mosquito populations build through spring and hit their highest numbers in mid to late summer. July and August are typically the worst months for sheer volume of bites, when warm temperatures, long days, and accumulated rainfall have created ideal breeding conditions for weeks on end.
Time of day matters too. The hours from dusk to dawn are peak biting times for many species, though some mosquitoes bite actively during the day as well. If you’re outdoors in the early evening during July or August, you’re in the crosshairs.
Disease Risk Peaks Late in the Season
The risk of mosquito-borne illness doesn’t track perfectly with mosquito numbers. West Nile virus, the most common mosquito-transmitted disease in the continental U.S., spreads during a window that typically runs from June through October. But the number of diagnosed cases peaks in late August to early September. That’s because the virus needs time to cycle between mosquitoes and birds before enough mosquitoes carry it to pose a serious risk to people. By the time you’re thinking about fall, the virus has had months to amplify in the mosquito population.
This means your highest risk of getting sick isn’t at the start of mosquito season when the biting first begins. It’s toward the end of summer, when you might already be letting your guard down.
Mosquito Season Is Getting Longer
Rising temperatures are stretching mosquito season in much of the country. A Climate Central analysis of 242 U.S. locations found that 71% experienced an increase in annual “mosquito days” between 1979 and 2022, gaining about 16 days on average. That translates to earlier starts in spring, later endings in fall, or both.
For people in northern states who once relied on cool September nights to end the season, those extra weeks matter. Warmer autumns keep mosquitoes active and biting longer, extending the window for both nuisance bites and disease transmission. In tropical and subtropical climates, mosquitoes are already active nearly year-round, so the shift is less noticeable. But in temperate zones, the expansion is measurable and ongoing.
What You Can Do During Mosquito Season
The most effective step is eliminating standing water around your home. Mosquitoes can breed in as little as a bottle cap’s worth of water, so emptying plant saucers, cleaning gutters, and flipping over anything that collects rain makes a real difference. Do this weekly, since eggs can hatch in as little as a few days under warm conditions.
When you’re spending time outside during peak hours, long sleeves and EPA-registered repellents provide the most reliable protection. Fans on porches and patios help too, since mosquitoes are weak fliers and struggle in even moderate wind. If you live in the South or along the Gulf Coast, these habits need to start as early as February or March rather than waiting for the traditional Memorial Day cookout to remind you.