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Des Moines Mosquito Forecast

Today's mosquito activity in Des Moines, the week ahead, and what to do about it. Updated hourly.

Bite Index · Sunday, November 8

Low

Mosquito activity in Des Moines is low today.

Few mosquitoes. You may see one or two at dusk near water.

About normal for November in Polk County (typically around 0).

  • Off-season: even with rain and warmth, populations are a fraction of summer's.
  • Only 0.3 in. of rain Oct 13–Oct 28, so few new breeding sites; what's biting is coming from irrigation, pools and creeks.
  • At a two-week average of 55°F, larvae develop slowly and the population stays small whatever the rain.

The week ahead

Each day's Bite Index, from this week's weather and the rain that is still hatching. Forecast days get less certain as the week goes on.

  1. Today
    0Low61°/40°dry
  2. Mon
    0Low62°/37°dry
  3. Tue
    0Low62°/40°dry
  4. Wed
    0Low57°/43°dry
  5. Thu
    0Low43°/31°dry
  6. Fri
    0Low42°/28°dry
  7. Sat
    0Low51°/29°dry

Protect tonight

You can probably skip repellent tonight.

  1. If you're near a creek, pond or heavy shade at dusk, a light application on ankles and arms is plenty.
  2. Good night to tip out any containers holding water; what you empty now won't hatch next week.
Which repellent, and how much: DEET vs picaridinBest natural repellents

Why Des Moines's mosquitoes do what they do

Des Moines sits where the Raccoon River meets the Des Moines River, in a floodplain city with hot, humid summers and a short, intense mosquito season. Polk County runs larviciding and surveillance; the city itself has debated its spray budget in recent years, which makes the county's program and your own yard the main lines of defense.

  • Two rivers: floodplain backwaters and Gray's Lake hold water through the summer.
  • Humid Midwest summers: July dusk conditions are ideal for flight.
  • Culex tarsalis and pipiens: both West Nile vectors are present; Iowa records cases most years.
  • Short season: June through September; the index is zero from October to May.

A typical year in Polk County

What the Bite Index typically reads here each month, from Polk County's 30-year climate normals run through the same model as today's number. The month you're in is marked; the season map shows the same long-run picture for every county.

  1. JJanuary: 0
  2. FFebruary: 0
  3. MMarch: 0
  4. AApril: 0
  5. MMay: 14
  6. JJune: 57
  7. JJuly: 76
  8. AAugust: 73
  9. SSeptember: 50
  10. OOctober: 8
  11. NNovember: 0
  12. DDecember: 0

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Polk County's health department traps and tests mosquitoes through the season and publishes positive West Nile pools by ZIP code. When your ZIP has an active advisory, follow it regardless of today's number.

How the Bite Index is scored

The index is a model of conditions, not a mosquito count. Warmth and water set the size of the population, tonight's weather sets how much of it flies, and the season and local reports adjust the result. Every factor and today's value for it is listed here so you can check the number yourself. Warmth and Water are exactly the climate core of our county-level mosquito season map; the map shows that core on 30-year normals for every county, and “typical for this month” is the same model run on this county's normals, so the comparison is like for like.

WWater

Rain over the egg-to-adult window (0.3 in. between Oct 13 and Oct 28), expressed as a monthly rate on the same wetness curve the season map uses. At summer temperatures eggs become biting adults in about a week, so today's mosquitoes are last week's rain. Cool weather stretches the window; hot dry days shrink it. Irrigation, creeks and pools keep a 35% floor even in a drought.

Role scales
Today 0%

TWarmth

The trailing two-week average temperature on the season map's curve: nothing below 50°F, full speed at 78–88°F, a small penalty in extreme heat. Multiplied with Water, so a cool fortnight caps the index however wet it has been.

Role gates
Today 16%

ATonight

Whether the population that exists will actually fly and bite this evening: dusk temperature (65–85°F is ideal), wind (they stop flying around 10 mph), humidity, and rain around sunset. Scales the index between half and full.

Role 0.5–1×
Today 0%

GGround truth

A nudge from local trap counts and reports when we have them. For Des Moines this is neutral today; the health department's surveillance is linked above and will feed this factor as we wire it in.

Role ±15%
Today neutral

SSeason gate

A multiplier from the calendar: fully open in the city's season months, half-open in the shoulder months, nearly closed in deep winter unless the week is warm. Below a 50°F weekly average the index is simply 0.

Role ×
Today 15%

index = 100 × S × [T × (0.35 + 0.65·W)] × (0.5 + 0.5·A) × (1 + 0.15·G)

Bands: Low 0–20 · Moderate 21–40 · High 41–60 · Very High 61–80 · Severe 81–100. Weather is from Open-Meteo (observations and the 7-day forecast), refreshed hourly. The lag and temperature thresholds follow published work on Culex and Aedes development (Rueda et al. 1990; Cornell NRCC degree-day emergence; JAMCA 2024 on rainfall two to four weeks before trap peaks).

Questions people ask about mosquitoes in Des Moines

When is mosquito season in Des Moines?
June through September, peaking in July and August. The first frost, usually October, ends it.
Why are the mosquitoes so bad along the rivers?
The Raccoon and Des Moines floodplains hold water for weeks after high water, and the riverside parks hold humidity at dusk. Gray's Lake and Water Works Park run well above the citywide index.
Is West Nile virus a risk in Des Moines?
Yes. Iowa records West Nile cases most years and Polk County detects it in mosquitoes most summers. The county's and Iowa HHS's announcements are authoritative; follow them over the index.
Where does this forecast's data come from?
Open-Meteo weather for downtown Des Moines, scored by our documented model and compared with Polk County's season-map climatology. Not a trap count.

Also covers West Des Moines, Ankeny, Urbandale, Johnston, Altoona, Waukee, Gray's Lake, Water Works Park: the forecast point is central Des Moines, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 4:28 PM local time.

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