Guides

• When Does Mosquito Season Start? Dates Across the US — Mosquito season starts anywhere from winter to late spring. How 3,118 US counties split by start month, and why to act two weeks earlier.
• When Do Mosquitoes Go Away? The End of the Season — Mosquitoes stop biting when days cool below about 50F or a hard freeze hits. When that happens across 3,118 US counties, and why they come back in spring.
• West Nile Virus by County: How to Read the Case Counts — CDC recorded 62,990 human West Nile cases in US counties, 1999-2025. What a county count means, why big counties look worse, and when it peaks.
• Where Mosquito Season Never Ends — 22 US counties have no mosquito off-season in a normal year, and 99 more lose fewer than five weeks. Which ones, and what that changes.
• How the Mosquito Season Dates Are Worked Out — How NOAA climate normals become start, end and peak dates for 3,140 counties, how stations are matched, and where the numbers are weakest.