Mosquito season in Ransom County, ND: when it starts and ends

Mosquito months in Ransom County

In a normal year mosquito season in Ransom County, ND starts around May 4 and ends around October 3, about 22 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Ransom County, and when

• Start tipping out standing water weekly by April 20.
• Book any yard treatment for early May, ahead of the July peak.
• Repellent can go away after October 3.
• 4 West Nile cases since 2016 (last 2021): you should use repellent at dusk July to July, more so if over 60.

Ransom County against the rest of ND

Ransom County has the 12th longest season of 53 ND counties, at 153 days against 160 in Sheridan County and 135 in Rolette County. Its mean temperature is 41.6°F.

• Burleigh County: May 4 to October 4 (154 days, 128 WNV)
• Sargent County: May 3 to October 4 (153 days, 8 WNV)
• Oliver County: May 4 to October 3 (152 days, 1 WNV)
• Stutsman County: May 4 to October 3 (152 days, 20 WNV)

West Nile in Ransom County

From 1999 to 2025, CDC ArboNET counted 29 human West Nile cases in Ransom County (4 neuroinvasive) across 10 years. The worst was 2003 with 11; the latest was 2021.

Background: reading the West Nile counts; how the dates are worked out.