Timing
When is mosquito season?When is mosquito season? A month-by-month map for every US county
Mosquito season starts when nights stay above 50°F and there is standing water to breed in. Slide through the year to see when it starts, peaks and ends where you live.
By the Notch Wellness team · Updated November 6, 2026 · Reviewed against our scoring methodology
The short answer
The rule
50°F and standing water
Mosquitoes fly once nights stay above about 50°F, and they breed wherever rain, irrigation or a clogged gutter leaves water standing for a week. Both have to be true for a real season.
Where it never ends
Gulf Coast, Florida, Hawaii
South Florida, the Gulf Coast and Hawaii never get a true off-season. The northern tier and the mountain West get a few summer months, roughly May or June through September.
Heat alone is not enough
Dry heat stays low
Phoenix in June is hotter than Ohio and has fewer mosquitoes. Without rain, a hot city runs "low" until the monsoon arrives in August.
Every state has a different answer, and inside a state the answer changes from the coast to the hills. The map below scores every county in the country for every month of the year. Slide to a month, click your state to zoom in, and click a county to pin it. The summary underneath shows the season window, the peak months, and when people near you actually report mosquitoes.
July
- Asleep below 50°F
Too cold to fly. Adults die or go dormant; eggs wait it out. - Low cool, or warm but dry
A few around, mostly at dusk. Either barely warm enough, or hot with nowhere to breed. - Active warm with some rain
Breeding in whatever water is around and biting most evenings. - Peak hot and wet
Fast breeding, the most bites and the highest disease risk. Reapply hourly outside.
United States
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Activity index: NOAA’s long-term monthly temperature and rainfall for each county, blended with the months people in each state actually report mosquitoes on iNaturalist. County averages blend valleys and mountains, so a warm city can run a few weeks ahead of its county. Alaska and Hawaii are statewide estimates.
How the map is scored
The level you see is our own scoring of climate and sightings, not a measured mosquito count. Three inputs go into it. The first is temperature: NOAA's long-term average for each county and month. Below 50°F the month scores zero, because adults cannot fly and either die or go dormant. From 50°F up to the high 70s the score climbs, standing in for faster breeding and biting as it warms, and it eases off slightly in extreme heat above about 88°F.
The second is rain, as a stand-in for standing water. Under half an inch in a month counts as nothing; two and a half inches counts as fully wet. Because a mosquito takes a week or more to go from egg to biting adult, and puddles outlast the calendar, 40 percent of last month's rain carries into this month's score. A hot, dry place never scores zero on water, since irrigation, pools, gutters and birdbaths keep some mosquitoes going anywhere people live.
The third is people. iNaturalist holds roughly 96,000 public mosquito sightings across the country. For each state we take the share of all sightings that are mosquitoes in each month, which corrects for the fact that people photograph everything more in summer, and use that curve to reshape the climate score. It can move a state's season around, giving the Gulf Coast its spring and fall peaks with a midsummer lull or Arizona its August monsoon peak, but it cannot make Seattle look like Houston. Sightings are state-level, so they adjust every county in a state the same way.
"Low" covers two different situations: a month that is only just warm enough, and a month that is warm but dry. Either way, expect a few mosquitoes at dusk rather than a swarm.
What the map can't see
Each county gets one average, so a county that runs from a warm valley to a cold ridge is scored somewhere in between. A city in the valley can be a few weeks ahead of the color on the map, and a town in the hills a few weeks behind. The same goes for a sheltered backyard against an open field.
The map also cannot see your yard. The rain input is a proxy for standing water, and in a dry month the mosquitoes that remain are breeding in whatever people provide: a kiddie pool, a saucer under a plant, a gutter that never drains. A "low" month can be an active one on a single street. If you are getting bitten when the map says you should not be, the water is close to home.
The year, region by region
Statewide windows from the map. Individual counties run earlier or later.
South Florida, Gulf Coast, Hawaii
Year-round
Florida, Louisiana and Hawaii never drop to asleep. Florida and the Gulf states peak May through October or November, with the heaviest sightings in late summer and early fall. Hawaii scores peak every month of the year.
The South and Texas
March – November
Alabama, Georgia, Mississippi, Arkansas, South Carolina and Texas wake up in March, peak from May into September or October, and fade in November. Texans report the most mosquitoes in June and again in October and November.
Mid-Atlantic, Ohio Valley, lower Midwest
April – October
Virginia, Maryland, Delaware, Kentucky, Tennessee, Missouri, Illinois, Indiana and Kansas start in April, peak June through September, and are done by the end of October.
Northeast and upper Midwest
May – September or October
New York, New England, Michigan, Wisconsin, Minnesota, Iowa and the Dakotas start in May and peak for a short stretch in July and August. Minnesota, Wisconsin and North Dakota hit a true peak for only about a month.
Mountain West and Pacific Northwest
May – September, mostly low
Colorado, Utah, Montana, Idaho, Wyoming, Washington and Oregon are warm enough from late spring, but dry summers keep most of the region at low or active rather than peak. Wetter mountain valleys and river bottoms run hotter than the state average.
Desert Southwest
March – October, with a monsoon peak
Arizona and New Mexico are warm for most of the year but score low through the dry spring and early summer. The season peaks in August and September, when the monsoon brings rain, and people in both states report the most mosquitoes from August through October.
California
April – November, mostly low
Mild temperatures keep California active for most of the year, but the dry summer means the state never hits a true peak. Irrigated valleys and the delta are the exception, and Californians report the most mosquitoes in September through November.
Alaska
June – August
A short, intense season around the summer solstice. The statewide estimate understates the interior, where thawing muskeg produces legendary clouds of mosquitoes in June and July.
Common questions
- What temperature do mosquitoes come out at?
- About 50°F. Below that, adult mosquitoes cannot fly well and either die or go dormant, and eggs wait for warmer weather. Activity picks up steadily as nights move into the 60s and 70s, which is why a warm spell in March can bring the first bites weeks before the calendar says so.
- When does mosquito season end?
- When nights drop back below about 50°F for good. In the northern half of the country that is late September or October; in the South it is November; along the Gulf Coast, in South Florida and in Hawaii it never really happens. The first hard frost ends the season for the adults, but their eggs survive the winter.
- Why are there so few mosquitoes in Phoenix in June when it is so hot?
- Because there is nowhere to breed. Mosquitoes need water that stands for about a week, and a desert June offers almost none outside irrigated yards. The map scores Phoenix low through the dry heat and peak once the August monsoon arrives.
- Is the level on the map a real mosquito count?
- No. It is our scoring of NOAA's long-term temperature and rainfall for each county, reshaped by the months people in each state report mosquitoes on iNaturalist. It tells you when conditions favor mosquitoes where you live, not how many are in your yard, which depends on standing water close to home.
- Why does the map show a county as asleep when I am getting bitten?
- Two common reasons. A county is one average, and a warm valley or city can run a few weeks ahead of its county. And some species breed indoors or in small containers that stay warm; a few mosquitoes in a garage or a basement drain can bite well into a cold month. Check our guide to indoor mosquito control if the bites are happening inside.
- When should I start using repellent?
- When your area turns from asleep to low on the map, which is the first month with average temperatures above 50°F. Have a repellent in the bag by then and keep it there until the map goes back to asleep in the fall. In year-round areas, treat it like sunscreen.