Today's Mosquito Risk in South Dakota: Real-Time Forecast & Activity Map
Check your ZIP code for local mosquito activity, West Nile risk, and prevention insights.
Built from CDC and NOAA data
Mosquito Surveillance Insights
- Annual WNV Cases
- about 50 to 100 confirmed cases annually
- roughly 9 to 10 per 100k cumulative incidence (top 3 in country)
- Based on CDC ArboNET surveillance data
- Risk Tier
- Tier 2: High Pressure
- Highest per-capita WNV exposure rates of any state alongside North Dakota; small population masks the scale.
- Per mosquito-risk-model regional tier
- Highest-Risk Areas
- Minnehaha, Pennington, Brown (metros); prairie pothole and James River counties (Cx. tarsalis)
Current Situation in South Dakota
South Dakota carries one of the top three per-capita WNV burdens in the country at roughly 9 to 10 cases per 100,000 cumulative incidence, with about 50 to 100 confirmed human cases annually distributed across the Sioux Falls, Rapid City, and Aberdeen metros and the prairie pothole counties of the eastern and central tier. The small population masks the scale of exposure. The state sits in the Plains Cx. tarsalis regime, and the agricultural Culex drives WNV transmission across the prairie pothole region and the Missouri River bottoms. Aedes vexans floodwater hatches follow heavy summer storms and spring snowmelt. Aedes albopictus is rare. EEE is rare. The Black Hills run cooler and drier than the prairie east of the Missouri River and carry lower mosquito pressure. Biting season runs June through September.
Snapshot of the current mosquito situation in South Dakota, drawn from CDC ArboNET surveillance and the regional risk model.
- Risk Level
- Moderate
- Peak Activity
- June through September
- Dominant Vector
- Western Encephalitis Mosquito (Culex tarsalis) statewide and dominant WNV vector
Where Mosquitoes Breed in South Dakota
South Dakota mosquito habitat is built on the prairie pothole region east of the Missouri River and the Missouri River bottomlands. Glacial pothole wetlands across the eastern counties from Brown and Marshall down through Minnehaha produce massive Aedes vexans hatches off snowmelt and steady summer Cx. tarsalis populations off the irrigated farm grid. Sand Lake National Wildlife Refuge in the northeast and Lacreek National Wildlife Refuge in the southwest sit at the heart of the prairie pothole habitat. The Missouri River bottomlands and Lake Oahe shoreline carry seasonal Aedes vexans floods and steady Cx. tarsalis populations. The James River and Big Sioux River corridors hold dense agricultural Culex through summer. The Black Hills hold ponderosa pine forest with cooler and drier conditions, and Custer State Park sees lighter pressure than the prairie. The Badlands run hot and dry with limited mosquito habitat.
Hotspot Counties & Areas
- Minnehaha County (Sioux Falls metro)
- Pennington County (Rapid City, Black Hills edge)
- Brown County (Aberdeen, prairie pothole region)
- Missouri River bottomlands and Lake Oahe shoreline
- Sand Lake National Wildlife Refuge
- Lacreek National Wildlife Refuge
- Custer State Park (Black Hills)
- James River corridor
Seasonal Activity Pattern
Biting starts in late May across the eastern prairie counties off snowmelt, mid June statewide, peaks late July through August, and tapers through September. WNV cases concentrate in August across the prairie pothole counties and the Sioux Falls and Rapid City metros. Cx. tarsalis populations build through July with the irrigation cycle and stay elevated through August. Spring snowmelt off the prairie pothole region produces heavy Aedes vexans hatches from late May through June. Heavy summer thunderstorms produce sharp Aedes vexans pulses along the James River, Big Sioux, and Missouri bottoms. The Black Hills run a week or two cooler than the prairie and carry lower late-summer biting pressure.
Monthly Biting Intensity (Plains)
South Dakota Mosquito Risk Profile
- WNV burden level
- Moderate
- about 50 to 100 confirmed cases annually; roughly 9 to 10 per 100k cumulative incidence (top 3 in country)
- EEE risk
- Rare
- Peak biting season
- June through September
- Top urban risk areas
- Sioux Falls (Minnehaha)
- Rapid City (Pennington)
- Aberdeen (Brown)
Signature habitat: prairie potholes, Missouri River bottoms, Black Hills meadows, James River floodplain.
Climate driver: Highest per-capita WNV exposure rates of any state alongside North Dakota; small population masks the scale.
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Common Mosquitoes in South Dakota
Understanding which mosquitoes are active in South Dakota helps you identify threats and take appropriate precautions. Click any card for details.
Northern House Mosquito
Culex pipiens
Risk: West Nile virus, St. Louis encephalitis, dog heartworm.
Key feature: Medium brown body with banded abdomen. Looks nearly identical to Cx. quinquefasciatus.
Active: Late spring through early fall in the north. Adult females overwinter in basements, garages, and storm drains.
Inland Floodwater Mosquito
Aedes vexans
Risk: Aggressive nuisance biter. Weak vector for West Nile, dog heartworm.
Key feature: Brown body with pale bands on the legs and a tapered abdomen.
Active: Spring through fall. Population spikes a week or two after major rain events.
West Nile Virus
Vector: Northern House Mosquito
West Nile Virus
The dominant West Nile vector across the northern half of the US. About 80% of infections are asymptomatic.
What to watch for
- Onset typically 2 to 15 days after a bite
- Most cases mild or asymptomatic, small fraction severe
- Neurological signs (severe headache, neck stiffness, confusion) need ER care
Breaking the Cycle in South Dakota
The mosquito lifecycle takes about a week. These habits cut local biting pressure faster than anything else, building multiple layers of protection.
Drain the Yard Weekly
Empty buckets, planter saucers, kiddie pools, tarps, and clogged gutters. A week of standing water is one full mosquito generation.
Repel Before Going Out
EPA-registered DEET (20-30%), picaridin (20%), IR3535, or oil of lemon eucalyptus. Apply before going outside, especially at dusk and dawn.
Seal the House
Window and door screens with no tears. AC and porch fans both work. Mosquitoes struggle to fly upwind even at 1-2 mph air speed.
Treat Outdoor Clothing
Permethrin-treated long sleeves and pants for evening yard work, hiking, or fishing. Remains effective through 70+ wash cycles.
If You Develop Symptoms
Most mosquito bites are harmless. A small fraction can transmit illness, and knowing the timeline matters more than panicking at every itch.Five things to know.
Watch for fever
Fever, body aches, headache, or fatigue 2 to 15 days after a bite. West Nile often feels like flu, and most infections never get diagnosed.
Note where and when
A rough record of where and when you got bitten helps your doctor decide what to test for. Date, location, mosquito-heavy areas you visited.
Get help fast for neuro signs
Severe headache, neck stiffness, confusion, vision changes, or sudden muscle weakness can mean neuroinvasive WNV or EEE. Both are medical emergencies.
Pregnant exposure?
If pregnant and bitten in an area with documented Zika or local dengue transmission, mention to your OB. Same goes for travel exposure.
Children and seniors
Higher risk of severe disease from WNV, EEE, and dengue in adults over 60 and children under 5. Early call to the pediatrician or PCP if symptoms appear.
When does mosquito season end in South Dakota?
Mosquito activity winds down after the first hard freeze, which in South Dakota typically arrives around Sep 30. See the local first-frost window and city-by-city freeze dates.
South Dakota first frost datesAlso worried about ticks in South Dakota?
Lyme disease risk and tick activity track different seasonal patterns than mosquitoes. See your South Dakota tick forecast.
View South Dakota tick forecastStay Safe in South Dakota
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