Mosquito season in Cass County, ND: when it starts and ends
Mosquito months in Cass County
In a normal year mosquito season in Cass County, ND starts around May 3 and ends around October 4, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Cass County, and when
- Start tipping out standing water weekly by April 19.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 4.
- 79 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July, and check ND spray notices.
Cass County against the rest of ND
Cass County has the 8th longest season of 53 ND counties, at 154 days against 160 in Sheridan County and 135 in Rolette County. Its mean temperature is 41.1°F.
- LaMoure County: May 2 to October 5 (156 days, 6 WNV)
- Walsh County: May 2 to October 4 (154 days, 5 WNV)
- Emmons County: May 3 to October 4 (154 days, 4 WNV)
- Burleigh County: May 4 to October 4 (154 days, 128 WNV)
West Nile in Cass County
From 1999 to 2025, CDC ArboNET counted 213 human West Nile cases in Cass County (63 neuroinvasive) across 17 years. The worst was 2007 with 49; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.