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When Is Mosquito Season?

By Andrew Rothaus, Founder ·

Mosquito season depends on where you are. New York's health department says mosquitoes there are active from early summer until late fall, and that in warm southern states, disease-spreading mosquitoes are active year round. Nebraska's health department says activity continues until a sustained hard freeze. The CDC puts West Nile diagnoses at a typical late August to early September peak.

The sun setting over a still lake with brush along the shoreline at dusk

Mosquito season is really three calendars stacked on each other: temperature, species, and rainfall.

What temperature does it take for mosquitoes to become active?

There is no single switch. Thresholds are species-specific. In Minnesota, the Metropolitan Mosquito Control District reports that spring Aedes mosquitoes overwinter as eggs in woodland pools and marshes, and that "when temperatures exceed ~39 degrees Fahrenheit, spring Aedes eggs hatch." The Washington State Department of Health gives a higher number for a different group. Writing about the floodwater species Aedes vexans and Ae. sticticus along the Columbia River, its 2025 guidance says that when temperatures are below 45 to 50 degrees F, the eggs of these species are dormant, so only some of the eggs hatch after a spring flood.

Temperature also sets the pace. The EPA says the mosquito life cycle "typically takes up two weeks, but depending on conditions, it can range from 4 days to as long as a month," and that hatch time "depends on water temperature, food and type of mosquito." The CDC's typical figure is 7 to 10 days from egg to adult for both Culex and Aedes. Writing during an unusually early Keys season, the Florida Department of Health in Monroe County noted that larvae "tend to develop into adult mosquitoes more quickly as temperatures climb."

For disease transmission specifically, Shocket and colleagues modeled ten mosquito and virus pairs in eLife in 2020. Transmission is optimized at intermediate temperatures of 23 to 26 degrees C, roughly 73 to 79 degrees Fahrenheit, and incidence of human neuroinvasive West Nile disease responded unimodally to average summer temperature, peaking at 24 degrees C. Among the three North American Culex vectors, the modeled lower thermal limit for West Nile ranged from 19.0 degrees C in Cx. quinquefasciatus to 12.2 in Cx. tarsalis. The authors flagged their own limits: the human disease data "did not show evidence for lower or upper thermal limits."

How long does mosquito season last in your region?

The New York State Department of Health draws the contrast in two sentences. Its own state: mosquitoes "are active from early summer until late fall in New York State." Elsewhere: "In southern states that have warm year-round weather, mosquitoes that can spread diseases are active throughout the year."

Agency calendars fill in the middle. Washington State says mosquito surveillance "should typically begin in April or May and continue through September or early October." Minnesota tells residents their risk runs "primarily July through September." Nebraska's health department frames the endpoint as a hard freeze: "Until we experience a sustained hard freeze, we will continue to see mosquito activity."

Modeling caps the northern season hard. Mordecai and colleagues, in PLOS Neglected Tropical Diseases in 2017, found dengue, chikungunya, and Zika transmission occurring between 18 and 34 degrees C, and concluded that "transmission in temperate areas is limited to at most three months per year even if vectors are present." That is transmission suitability, not how many months mosquitoes bite. Burden is uneven too: the EPA's West Nile indicator puts average annual incidence "highest in parts of the Southwest, the Mississippi Delta region, the Great Plains, and the Rocky Mountain region."

Which species dominate at which point in the season?

Minnesota's control district publishes a month-by-month account. Spring Aedes hatch from overwintered eggs as snow melts, and by mid-June they "begin to die out." Cattail mosquitoes take one annual brood "peaking around the 4th of July." Then Culex takes over: "Culex restuans decrease in numbers and Culex pipiens reach their peak in mid-August. Due to these mosquitoes' large numbers, August becomes the time of year where people are most at risk to contract West Nile Virus."

That late-summer Culex peak is why bite season and disease season are not the same thing. The CDC says West Nile infections happen "during mosquito season, which starts in the summer and continues through fall (typically June through October)," with diagnoses typically peaking "in late August to early September." The same window shows up in Georgia, where University of Georgia Extension has described southern house mosquitoes as most active, and West Nile transmission as most common, during late summer and early fall and the period from August 15 to September 15.

Behavior changes with the handoff, which decides when you need cover. The CDC says adult Culex "are most active from dusk to dawn," and that some "prefer to live near and bite birds," biting people when other animals are not nearby. Container Aedes are the opposite: UGA Extension calls Asian tiger mosquitoes "voracious daytime feeders" that "lay eggs and develop in anything that can hold water," naming clogged downspouts, watering cans, toys, and plant saucers. Per the CDC, these species "will only fly a few blocks" in their lifetime, so the problem is usually your yard or your neighbor's.

Why does standing water after rain drive a local surge?

Because a whole class of mosquito spends the dry weeks as eggs waiting for exactly that. Penn State Extension describes the floodwater group depositing eggs "singly on damp soil in grassy or woodland depressions" that flood intermittently, where they "may remain dormant and viable on the soil for some time until the area is flooded." Then: "Typically, large numbers hatch simultaneously. The larvae develop synchronously, and adults begin to appear as early as 7 days after flooding."

Minnesota's control district adds a rain gauge. Summer floodwater mosquitoes take "around a week to mature into adults," and "with every rainfall exceeding an inch, a new brood of summer floodwater mosquitoes will hatch and emerge."

Container species run the same trigger at smaller scale. The CDC says Aedes eggs stick to container walls above the waterline, "can survive drying out for up to 8 months," and hatch "when water (from rain or a sprinkler) covers the eggs." A sprinkler counts, which is how a rain-free week still produces mosquitoes.

After major weather the CDC is specific about sequence. The CDC expects nuisance and floodwater mosquitoes to increase "in the weeks after flooding." Separately, "the types of mosquitoes that can spread viruses may increase 2 weeks after a hurricane," including "in areas that did not flood but received more rainfall than usual," and "it can take several more weeks before mosquitoes could start spreading viruses to people." The CDC also states that "an increase in the number of people getting sick from germs spread by mosquitoes is not expected after flooding."

What do public health agencies recommend during mosquito season?

The CDC's advice is the same all season:

  • Use EPA-registered insect repellents with one of these active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol, or 2-undecanone. Look for an EPA registration number on the label.
  • Wear loose-fitting, long-sleeved shirts and pants, plus clothing and gear treated with permethrin. The CDC says not to use permethrin products directly on skin.
  • Use screens on windows and doors, repair holes, and use air conditioning when available.
  • Once a week, empty and scrub, turn over, cover, or throw out items that hold water: tires, buckets, toys, pools, birdbaths, flowerpot saucers.
  • The CDC advises against products containing oil of lemon eucalyptus or para-menthane-diol on children under 3 years old. More in our guide to repellent for kids.

State agencies add local timing. New York tells residents to cover skin "at sunrise, sunset, and early in the evening when mosquitoes are most active." Minnesota frames it as knowing when and where you are at risk: July through September, open agricultural areas for West Nile virus, wooded areas for La Crosse and Jamestown Canyon viruses.

Nebraska's state epidemiologist adds the follow-up: "If you experience symptoms such as fever, headache, fatigue, or body aches after being bitten, contact a healthcare provider and mention your recent mosquito bite." Any decision about testing or treatment belongs with your clinician.

When does mosquito season actually end?

Later than most people assume, and not on a date. Washington State's guidance notes that all life stages except pupae can overwinter, that adults "hibernate in basements, culverts, mines, or other protected areas," and that eggs in floodplain soil "hatch when flooded, even several years later." Minnesota's control district describes adult Culex searching out "barns, caves, and any other warm habitat."

Farther south, some of that storage is barely dormant. The CDC notes Aedes eggs "can even survive a winter in the southern United States," and the EPA's indicator points out that "mild winters and drought have been associated with West Nile virus disease outbreaks."

Where Longsleeve fits

Longsleeve is an EPA-registered picaridin lotion (EPA Reg. No. 101457-1). It repels mosquitoes and ticks for up to 14 hours. It is fragrance-free, with nine disclosed ingredients.

Common questions

What temperature do mosquitoes stop being active at?

There is no single number, and the published thresholds describe eggs rather than adults. Minnesota's Metropolitan Mosquito Control District reports spring Aedes eggs hatching above about 39 degrees Fahrenheit. Washington State's health department says that below 45 to 50 degrees F, eggs of the floodwater species Aedes vexans and Ae. sticticus are dormant. For the end of the season, Nebraska's health department tells residents to expect activity until a sustained hard freeze.

Is there a mosquito season in the South, or is it year round?

The New York State Department of Health says that in southern states with warm year-round weather, mosquitoes that can spread diseases are active throughout the year. The same 2017 modeling in PLOS Neglected Tropical Diseases found tropical and subtropical regions suitable for extended seasonal or year-round transmission of dengue, chikungunya, and Zika.

Why are mosquitoes worse about a week after heavy rain?

Floodwater mosquitoes lay eggs on damp soil that stay dormant until flooding. Penn State Extension reports that large numbers hatch at once and that adults "begin to appear as early as 7 days after flooding." Minnesota's Metropolitan Mosquito Control District reports every rainfall over an inch producing a new brood of summer floodwater mosquitoes.

When is West Nile virus risk highest?

The CDC says infections occur during mosquito season, typically June through October, with diagnoses typically peaking in late August to early September. Minnesota's control district reports Culex pipiens peaking in mid-August, and University of Georgia Extension points to August 15 through September 15 in Georgia. More in our West Nile virus guide.

Sources

  1. CDC, About West Nile. https://www.cdc.gov/west-nile-virus/about/index.html
  2. CDC, About Culex Mosquitoes. https://www.cdc.gov/mosquitoes/about/culex-mosquitoes.html
  3. CDC, Life Cycle of Aedes Mosquitoes. https://www.cdc.gov/mosquitoes/about/life-cycle-of-aedes-mosquitoes.html
  4. CDC, What to Do After a Hurricane or Flood. https://www.cdc.gov/mosquitoes/response/index.html
  5. CDC, Preventing Mosquito Bites. https://www.cdc.gov/mosquitoes/prevention/index.html
  6. EPA, Mosquito Life Cycle. https://www.epa.gov/mosquitocontrol/mosquito-life-cycle
  7. EPA, Climate Change Indicators: West Nile Virus (January 2021 archived snapshot). https://19january2021snapshot.epa.gov/climate-indicators/climate-change-indicators-west-nile-virus_.html
  8. Washington State Department of Health, Guidance for Surveillance, Prevention, and Control of Mosquito-borne Disease, 2025 Edition (DOH 333-149). https://doh.wa.gov/sites/default/files/legacy/Documents/Pubs//333-149.pdf
  9. New York State Department of Health, Mosquitoes and Disease. https://www.health.ny.gov/diseases/mosquitoes/
  10. Minnesota Department of Health, Mosquitoes and Mosquitoborne Diseases of Minnesota. https://www.health.state.mn.us/diseases/mosquitoborne/mosquitobornediseases.pdf
  11. Metropolitan Mosquito Control District (Minnesota), Minnesota Mosquitoes: by the Month. https://mmcd.org/2025/01/07/minnesota-mosquitoes-by-the-month-2176/
  12. Nebraska Department of Health and Human Services, Mosquitoes are Still Active Despite Cooler Weather. https://dhhs.ne.gov/Pages/Mosquitoes-are-Still-Active-Despite-Cooler-Weather.aspx
  13. Florida Department of Health in Monroe County, Unseasonably High Temperatures Linked to Early, Active Mosquito Season in Florida Keys, July 14, 2023. https://monroe.floridahealth.gov/2023/07/14/unseasonably-high-temperatures-linked-to-early-active-mosquito-season-in-florida-keys/
  14. Penn State Extension, Mosquito Biology and Control. https://extension.psu.edu/mosquito-biology-and-control
  15. University of Georgia Cooperative Extension, Wet weather and heat fuel end-of-season mosquito boom, August 9, 2018. https://extension.uga.edu/story.html?story=Mosquito-Season&storyid=7676
  16. Shocket MS, Verwillow AB, Numazu MG, Slamani H, Cohen JM, El Moustaid F, et al. Transmission of West Nile and five other temperate mosquito-borne viruses peaks at temperatures between 23 degrees C and 26 degrees C. eLife. 2020;9:e58511. https://elifesciences.org/articles/58511
  17. Mordecai EA, Cohen JM, Evans MV, Gudapati P, Johnson LR, Lippi CA, et al. Detecting the impact of temperature on transmission of Zika, dengue, and chikungunya using mechanistic models. PLOS Neglected Tropical Diseases. 2017;11(4):e0005568. https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0005568

Last reviewed 2026-08-16 · every claim on this page is sourced above