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Indianapolis Mosquito Forecast

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

Bite Index · Sunday, November 8

Low

Mosquito activity in Indianapolis is low today.

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

About normal for November in Marion County.

  • Off-season: even with rain and warmth, populations are a fraction of summer's.
  • Tonight: a cool 48°F evening, light wind — poor flying weather, so fewer bites than the population alone would suggest.
  • Only 0.2 in. of rain Oct 14–Oct 28, so few new breeding sites; what's biting is coming from irrigation, pools and creeks.

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
    3Low59°/32°dry
  2. Mon
    3Low59°/35°dry
  3. Tue
    5Low66°/37°dry
  4. Wed
    0Low65°/50°0.2 in
  5. Thu
    0Low54°/38°0.3 in
  6. Fri
    0Low43°/35°dry
  7. Sat
    0Low45°/34°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 Indianapolis's mosquitoes do what they do

Indianapolis is flat and well-watered, with the White River, Fall Creek and Eagle Creek crossing the city and warm, humid summers. The Marion County Public Health Department traps and tests through the season and announces the first West Nile-positive mosquitoes each summer, usually in June or July.

  • Flat and slow-draining: rain stands in yards and ditches across the city.
  • River corridors: the White River and Fall Creek greenways are floodwater and Culex habitat.
  • Catch basins: urban Culex breed in storm drains; the county larvicides them.
  • Real winter: frosts from October end the season.

A typical year in Marion County

The long-run mosquito index by month from our season map (NOAA climate normals plus effort-corrected sightings). Today's Bite Index is the live version of this; the month you're in is marked.

  1. JJanuary: 0
  2. FFebruary: 0
  3. MMarch: 0
  4. AApril: 21
  5. MMay: 50
  6. JJune: 74
  7. JJuly: 86
  8. AAugust: 84
  9. SSeptember: 70
  10. OOctober: 46
  11. NNovember: 0
  12. DDecember: 0

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Marion 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. Four weather factors are combined on a 0–100 scale, then scaled by the season. Every factor and today's value for it is listed here so you can check the number yourself. It uses the same temperature curve and rain logic as our county-level mosquito season map, which has been validated against effort-corrected sighting data across 41 states.

BBreeding pressure

Rain 7–14 days ago (0.2 in. between Oct 14 and Oct 28). Eggs need water to hatch, and at summer temperatures the egg-to-biting-adult cycle takes about a week, so today's mosquitoes are last week's rain. Cool weather stretches the window; hot dry days shrink it as shallow water evaporates.

Weight 40%
Today 0%

DDevelopment

The trailing two-week average temperature, on the same curve as our national season map: nothing below 50°F, full speed at 78–88°F, a small penalty in extreme heat.

Weight 25%
Today 25%

ATonight's activity

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.

Weight 25%
Today 0%

GGround truth

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

Weight 10%
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.

Weight ×
Today 15%

index = 100 × S × (0.40 × (0.2 + 0.8·B) + 0.25 × D + 0.25 × A + 0.10 × (0.5 + 0.5·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 Indianapolis

When is mosquito season in Indianapolis?
May through September, peaking in July and August. The first frost, usually October, ends it.
Why are mosquitoes worse a week after it rains in Indy?
Flat ground holds rain in yards and ditches, and at summer temperatures eggs become biting adults in 7 to 10 days. The index looks back at exactly that window.
Is West Nile virus a risk in Indianapolis?
Yes. Marion County finds West Nile-positive mosquitoes every summer and reports human cases in most years. The health department's announcements are authoritative; follow them over the index.
Where does this forecast's data come from?
Open-Meteo weather for downtown Indianapolis, scored by our documented model and compared with Marion County's season-map climatology. Not a trap count.

Also covers Carmel, Fishers, Greenwood, Lawrence, Speedway, Noblesville, Eagle Creek Park, the Canal Walk: the forecast point is central Indianapolis, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 1:38 PM local time.

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