When does mosquito season end?
It's not a calendar date. It ends when temperatures drop and stay down. Here's what that means by region — and why some parts of the country barely get a break at all.
The short answer
Mosquito season ends when nighttime lows consistently fall below 50°F. At that temperature, adult mosquitoes become sluggish and stop feeding; below about 45–50°F they die or go dormant depending on the species. Larvae in standing water stop developing. "Season" is essentially the window between the last spring frost and the first sustained fall cold snap — which is wildly different depending on where you live.
In much of the Deep South and Florida, there effectively isn't a mosquito-free season. In Minnesota, the season might last four months. In Seattle, the season exists but is mild. The 48-hour forecast and current activity level on the home page reflects your local conditions in real time, which is more useful than any general calendar.
How temperature drives mosquito activity
Mosquitoes are cold-blooded. Their metabolism, flight capacity, and breeding speed are all functions of ambient temperature. At 50°F, development essentially halts. As temperatures rise toward 80°F, biting activity and breeding speed increase rapidly. Above the mid-90s, heat suppression kicks in — mosquitoes become less active in extreme heat, which is why a July heat wave sometimes offers unexpected relief.
The 50°F threshold is the key number at the end of season. Once night lows are reliably below 50°F for several days in a row, adult populations crash. It doesn't have to freeze — sustained cool nights are enough. An Indian summer with a warm week in October can briefly bring activity back, but once you've had a hard frost, most adult mosquitoes of temperate species are gone.
Eggs are a different matter. Many species overwinter as eggs in dry, protected locations — inside tires, in leaf litter, in dry soil at the edge of ponds. Those eggs are dormant but not dead. They hatch the following spring when temperatures warm and water is available. This is why draining and treating standing water in fall still has value — fewer surviving eggs means a smaller starting population next year.
Season by region
These are typical windows based on historical climate data. Warm or cold years can shift them two to four weeks in either direction. Check the home page for your current real-time level.
| Region | Season typically starts | Season typically ends | Length |
|---|---|---|---|
| South Florida / Keys | Year-round | Year-round | 12 months — no true off-season |
| Gulf Coast (TX, LA, MS, AL) | February – March | November – December | 9–10 months |
| Southeast (GA, SC, NC, TN) | March – April | October – November | 7–8 months |
| Mid-Atlantic (VA, MD, DC, NJ, DE) | April – May | October | 5–6 months |
| Northeast (NY, NE, MA, CT) | May – June | September – October | 4–5 months |
| Midwest (OH, IN, IL, MI) | May | September – October | 4–5 months |
| Great Plains (MN, WI, IA, NE) | May – June | September | 3–4 months |
| Mountain West (CO, UT, WY) | June | August – September | 2–3 months |
| Southwest (AZ, NM) | April – May | October – November | 6–7 months (monsoon amplifies summer peak) |
| Pacific Coast (CA, OR, WA) | April – May | September – October | Highly variable; coastal areas milder, lower density |
The warm year effect
If it feels like season used to end earlier, it probably did. A 2023 Climate Central analysis found peak mosquito season has expanded by an average of 16 days per decade across US cities since the 1980s — with the largest gains in northern cities like Minneapolis, Chicago, and Detroit that previously had short seasons.
Average mosquito seasons have been getting longer. A 2023 analysis from Climate Central found that peak mosquito season (measured by days with temperatures suitable for mosquito activity) has expanded by an average of 16 days per decade in many US cities since the 1980s. Northern cities like Minneapolis, Chicago, and Detroit have seen some of the largest relative increases, because those areas previously had shorter seasons and are now seeing later falls.
This isn't a political statement — it's observational data from temperature records. If it feels like mosquito season used to end earlier when you were a kid, that's likely a real change, not nostalgia.
October and November bites — why they still happen
Even in northern states, warm spells in October can bring mosquito activity back briefly. Culex pipiens — the most common US mosquito — goes into a dormant-like state called diapause when days shorten and temperatures cool, but a week of 70°F weather in October can temporarily interrupt that. You might get a few warm evenings of biting before the next cold snap finishes them off.
This is one reason the "mosquito season" framing is a bit misleading. It's more accurate to think of mosquito activity as a continuous variable that rises and falls with temperature — which is exactly what the activity model on this site tracks. When your local lows are in the 40s, activity is at or near zero. When they rise back to the 60s for a warm stretch, it rises again. The season ends not with a hard stop but with increasingly rare windows of activity until winter closes out the last of them.
How to know your own end-of-season
The most reliable personal signal: check the 10-day weather forecast for your location. When projected nighttime lows are consistently below 50°F, activity will drop sharply. When they're forecast to stay there, you're done for the season. The site shows this directly — a Level 0 on the activity model means nighttime temperatures are below the threshold and no meaningful activity is expected.
Fall yard checklist: Before winter, walk your property and drain, dump, or store any containers that could collect winter rain and provide early-spring breeding habitat. Empty rain barrels, store planters and saucers inside, and clean gutters. Fewer overwintering eggs means a smaller population to deal with come April.
Sources
- American Mosquito Control Association. Mosquito biology — life cycle and temperature dependence.
- Mordecai, E. A., et al. (2019). Thermal biology of mosquito-borne disease. Ecology Letters, 22(10), 1690–1708. (Temperature-development relationship.)
- Climate Central (2023). Longer mosquito seasons — US city data.
- Reiskind, M. H., & Lounibos, L. P. (2009). Effects of intraspecific larval competition on adult longevity and fecundity in Aedes aegypti and Aedes albopictus. Medical and Veterinary Entomology.
Check today's activity level and 48-hour forecast for your area on the home page, or browse our other mosquito guides.