Skip to content

San Antonio Mosquito Forecast

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

Bite Index · Sunday, November 8

Severe

Severe mosquito activity in San Antonio today. Expect to be bitten within minutes outdoors at dusk.

Swarming conditions. Expect bites within a minute or two outside at dusk.

Worse than a typical November in Bexar County (usually around 61).

  • 2.5 in. of rain Oct 22–Oct 31 has had time to hatch: this is the surge from that storm.
  • A two-week average of 70°F keeps populations growing, just more slowly than midsummer.
  • Tonight: a cool 62°F evening, a breeze — average conditions for biting.

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
    81Severe65°/60°1.2 in
  2. Mon
    80V·High63°/59°1.1 in
  3. Tue
    84Severe67°/60°0.1 in
  4. Wed
    86Severe76°/61°dry
  5. Thu
    85Severe75°/60°dry
  6. Fri
    74V·High67°/54°dry
  7. Sat
    77V·High69°/51°dry

Protect tonight

Treat the outdoors like a swarm: cover up and use a full-strength repellent.

  1. 25–30% DEET or 20% picaridin on every bit of exposed skin, plus permethrin-treated clothing for anything longer than a quick trip outside.
  2. Keep kids and pets in around dusk and dawn; schedule outdoor time for midday when it's hottest and driest.
  3. If your health department has an active West Nile advisory for your ZIP, follow it over anything on this page.
Which repellent, and how much: DEET vs picaridinBest natural repellents

Why San Antonio's mosquitoes do what they do

San Antonio sits on the Balcones Escarpment, where the Hill Country drops to the coastal plain, and its mosquitoes live on the river, the creeks and the irrigated yards that outlast the dry spells. Metro Health traps and tests through the warm months; in 2026 it found West Nile in a trap in early June, months ahead of the usual late-summer detections.

  • Flash floods: Olmos, Salado and Leon Creeks run dry for weeks, then fill every low spot in an afternoon.
  • Irrigation: lawn and landscape watering keeps container-breeding Aedes going through hot, dry stretches when wild habitat is baked.
  • Long season: Bexar County stays active into December in most years.
  • West Nile: Culex quinquefasciatus is the dominant urban species and tests positive most summers.

A typical year in Bexar 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: 24
  2. FFebruary: 25
  3. MMarch: 35
  4. AApril: 62
  5. MMay: 87
  6. JJune: 100
  7. JJuly: 95
  8. AAugust: 82
  9. SSeptember: 92
  10. OOctober: 81
  11. NNovember: 61
  12. DDecember: 39

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Bexar 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 (2.5 in. between Oct 22 and Oct 31). 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 100%

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 72%

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 74%

GGround truth

A nudge from local trap counts and reports when we have them. For San Antonio 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 100%

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 San Antonio

When is mosquito season in San Antonio?
April through November is the heart of it, with the worst stretches after spring and fall rains. Mosquitoes are present in mild winters; nights below about 50°F are what finally quiet them.
Why are mosquitoes worse after a storm in San Antonio?
Because so much of the year is dry, the eggs waiting in dry containers and creek beds hatch all at once when rain finally comes. Warm temperatures finish the cycle in about a week, so the surge arrives 7 to 14 days later.
Is West Nile virus a risk in San Antonio?
Yes. Bexar County mosquito pools test positive for West Nile most summers, and Metro Health issues advisories and spray notices when they do. Follow those over the index; this page measures nuisance biting, not disease.
Where does this forecast's data come from?
Open-Meteo weather for central San Antonio, scored with our own documented model, with the county's season-map climatology for context. It is not a trap count; Metro Health's surveillance is linked above.

Also covers New Braunfels, Boerne, Schertz, Helotes, Alamo Heights, Brackenridge Park, the River Walk, Government Canyon: the forecast point is central San Antonio, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 12:38 PM local time.

Related guides