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Boston Mosquito Forecast

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

Bite Index · Sunday, November 8

Low

Mosquito activity in Boston is low today.

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

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

  • Off-season: even with rain and warmth, populations are a fraction of summer's.
  • At a two-week average of 55°F, larvae develop slowly and the population stays small whatever the rain.
  • Tonight: a cool 46°F evening, light wind — poor flying weather, so fewer bites than the population alone would suggest.

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
    1Low56°/45°0.2 in
  2. Mon
    1Low53°/42°dry
  3. Tue
    1Low56°/40°dry
  4. Wed
    1Low56°/47°dry
  5. Thu
    1Low53°/48°0.2 in
  6. Fri
    1Low56°/48°1.6 in
  7. Sat
    0Low53°/42°0.3 in

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 Boston's mosquitoes do what they do

Boston's mosquitoes live in the salt marshes of Belle Isle and the harbor islands, the Charles and Mystic River banks, and the tens of thousands of catch basins the Suffolk County Mosquito Control Project larvicides each summer. The season is short and the state publishes West Nile and EEE risk levels by town every week from June to October.

  • Salt marsh: Belle Isle Marsh, Revere and the harbor islands produce salt-marsh broods on spring tides.
  • Catch basins: Culex pipiens, the West Nile vector, breeds in storm drains; the project treats them in waves.
  • Charles and Mystic Rivers: the Esplanade and the river parks hold humidity at dusk.
  • Short season: June through September; the index is zero from October to May.

A typical year in Suffolk County

What the Bite Index typically reads here each month, from Suffolk 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: 5
  6. JJune: 39
  7. JJuly: 60
  8. AAugust: 60
  9. SSeptember: 41
  10. OOctober: 6
  11. NNovember: 0
  12. DDecember: 0

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Suffolk 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 (0.8 in. between Oct 8 and Oct 23), 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 50%

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 17%

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 Boston 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 Boston

When is mosquito season in Boston?
June through September, peaking in July and August. The state's arbovirus surveillance runs June to October; frost ends the season.
Why does the state publish risk levels by town?
West Nile and EEE risk varies sharply between the salt-marsh and swamp towns and the urban core, so Massachusetts rates each town weekly from remote to critical. Boston is usually low to moderate; the swamp towns to the south are where EEE turns critical.
Is West Nile virus a risk in Boston?
Yes, in late summer. Boston mosquito pools test positive most years and the state records human cases. The weekly state update is authoritative; follow it over the index.
Where does this forecast's data come from?
Open-Meteo weather for downtown Boston, scored by our documented model with the northern breeding lag, and compared with Suffolk County's season-map climatology. Not a trap count.

Also covers Cambridge, Somerville, Brookline, Quincy, Newton, Revere, the Esplanade, Jamaica Pond: the forecast point is central Boston, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 5:28 PM local time.

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