For most of the United States, mosquito season runs from March through October, depending on where you live. The season is driven almost entirely by temperature: mosquitoes become active when temperatures consistently stay above about 60°F (15°C) and reach peak activity between 70°F and 80°F (21°C to 27°C). If you’re wondering whether it’s mosquito season right now, the simplest answer is to check your local overnight lows. Once those stay above 60°F, mosquitoes are flying and biting.
When Mosquito Season Starts and Ends by Region
The timing varies significantly across the country. In the South and inland Southwest, mosquitoes typically emerge in March and remain active through September or even into October. In New England, the northern Midwest, and the Pacific Northwest, the season is shorter, generally running from May through September. Southern Florida and parts of the Gulf Coast can see mosquito activity nearly year-round because temperatures rarely drop low enough to shut things down.
These windows aren’t fixed dates on a calendar. A warm spring pushes the start earlier; a cool, dry summer can suppress activity even in peak months. What matters is sustained warmth and standing water, not the month itself.
Temperature Controls Everything
Mosquitoes are cold-blooded, so their metabolism, flight ability, and reproduction all depend on ambient temperature. They can fly in a range of roughly 59°F to 90°F (15°C to 32°C), with the sweet spot for activity around 70°F (21°C). Their immature stages, the larvae and pupae developing in water, struggle to survive below 61°F (16°C) or above 100°F (38°C), with the best survival rates around 79°F (26°C).
When temperatures drop below 50°F consistently, most species either die off or enter a hibernation-like state called diapause. During diapause, their bodies undergo significant changes: producing compounds that act like natural antifreeze, storing energy reserves, and slowing their metabolism to a crawl. Some species survive winter as adults tucked into sheltered spots like storm drains, hollow logs, and crawl spaces. Others lay cold-resistant eggs in soil or at the edges of dried-up puddles, where the eggs can sit dormant for months and hatch when spring rains arrive.
Water Matters as Much as Heat
Warm temperatures alone don’t create a mosquito problem. Females need standing water to lay their eggs, and the larvae develop entirely in water before emerging as flying adults. That water doesn’t have to be a pond or a swamp. A bottle cap holding a tablespoon of rainwater is enough for certain species. Clogged gutters, plant saucers, old tires, birdbaths, and pet bowls are all common breeding sites around homes.
Rainfall is the main driver. Species that breed in temporary pools become far more abundant during and right after rainy periods. Eggs of some species require high humidity to survive and hatch within days of being laid, while others can remain viable in dry conditions for weeks or months, waiting for the next rain to flood their resting spot. This is why you often notice a surge in mosquito numbers a week or two after heavy rain: that’s the time it takes for eggs to hatch and larvae to mature into biting adults.
When Mosquitoes Bite During the Day
Not all mosquitoes follow the same schedule. The species that carry dengue and Zika (the black-and-white-striped varieties common in the southern U.S.) are most active at dawn and dusk. Culex mosquitoes, the primary carriers of West Nile virus, peak later in the evening, around 10 to 11 p.m. Anopheles species, associated with malaria in tropical regions, bite throughout the night and evening hours.
This means your risk isn’t limited to the classic “sunset mosquito hour.” If you’re outdoors in the early morning or working in a shaded yard during a humid afternoon, you can still get bitten, especially by Aedes species that are aggressive daytime feeders in shady areas.
Peak Disease Risk Months
Mosquito-borne illness in the U.S. is dominated by West Nile virus, and the CDC identifies June through October as the primary transmission window. Cases peak in late August to early September, which makes sense: by late summer, mosquito populations have had months to build, and the virus has had time to cycle between birds and mosquitoes, amplifying in the environment.
The practical takeaway is that early and mid-season mosquitoes are mostly a nuisance, while late-summer mosquitoes carry the highest disease risk. That’s the period to be most diligent about protection, particularly in states with historically high West Nile activity like Texas, California, Colorado, and Illinois.
The Season Is Getting Longer
Warming temperatures have measurably extended mosquito season. A study tracking West Nile virus transmission conditions from 1999 to 2024 found that the season has lengthened by an average of about 25 days across the U.S., starting roughly 4 days earlier in spring and ending about 20 days later in fall. The change varies by county, but the overall trend is consistent: mosquitoes are active for more of the year than they were a generation ago.
How to Protect Yourself During the Season
Repellents containing DEET remain the most studied option. A product with about 24% DEET provides roughly 5 hours of protection from bites, while one with 20% lasts about 4 hours. Lower concentrations (around 5 to 7%) offer only 1.5 to 2 hours of protection, so you’ll need to reapply more frequently. Picaridin and oil of lemon eucalyptus are also registered as effective alternatives.
Beyond repellent, reducing breeding habitat around your home makes a real difference. Dump any container holding standing water at least once a week. Clean gutters so they drain properly. Change birdbath water every few days. Mosquitoes don’t travel far from where they hatch, so eliminating water sources within your yard directly reduces the number biting you on your porch.
Clothing helps too, particularly during peak biting hours. Long sleeves and pants in light colors are less attractive to mosquitoes than dark clothing, and tightly woven fabrics are harder for them to bite through. If you’re spending extended time outdoors in the evening, treating clothing with permethrin adds another layer of protection that lasts through multiple washes.