When do ants come out in New Hampshire?

Ants become active once daytime temperatures consistently pass roughly 50°F, the standard insect-activity floor. In southern New Hampshire that threshold is crossed early-to-mid April: NOAA/NCEI 1991–2020 climate normals show Concord's average high climbing from 44°F in March to 58°F in April, with Nashua following a similar 45°F-to-59°F jump. Before that point, colonies stay dormant below the frost line, so a cold, late spring can push emergence back by a week or two.

How long does ant season last in NH?

Ant season in New Hampshire runs roughly April through November. Activity builds through May, peaks during the 75–95°F heat of June through August, and then tapers through September and October as highs fall back toward the ~50°F threshold. By late November, outdoor colonies have gone dormant for the year, entering diapause below the frost line until the following spring's warm-up begins the cycle again.

Why am I seeing ants in the winter?

A stretch of unusually warm winter weather can briefly reactivate a dormant outdoor colony, but that's uncommon. Far more often, persistent winter ant sightings mean a carpenter-ant nest is already established inside a heated wall void, where indoor warmth keeps a portion of the colony active regardless of outdoor temperature. Large black ants indoors in January or February are a strong signal to have the structure inspected rather than assume it's a one-off.

What does a winged ant indoors in spring mean?

A winged ant found indoors in late winter or early spring is a carpenter-ant swarmer, and per UNH Extension and other university sources, swarmers appearing inside a home almost always indicate an established nest within the structure itself — not just ants foraging in from outside. This is the single highest-value diagnostic signal on this page; it warrants a prompt professional inspection to locate the nest before it grows or spreads to a satellite colony.

When do carpenter ants swarm?

Carpenter ants swarm roughly March through June across the eastern United States, with New Hampshire's swarming concentrated in spring as colonies mature enough to produce winged reproductives. Mature colonies can be several years old and produce hundreds of swarmers annually. Swarmers seen only outdoors, on porches or siding, more likely point to a nearby outdoor colony, while indoor swarmers point to a nest inside the building itself.

When are pavement ants and odorous house ants worst?

Pavement ants and odorous house ants are worst indoors in spring and early summer, as warming temperatures ramp up foraging activity across the colony. Both are common warm-month nuisance pests in New Hampshire homes, entering through small foundation gaps in search of food and moisture. Activity generally follows the same 50°F-and-rising trend line as other ants, peaking alongside the broader summer surge in June through August.

Do carpenter ants eat wood like termites?

No — unlike termites, carpenter ants don't eat wood for nutrition. They excavate smooth galleries inside it, usually starting in wood that's already softened by moisture damage, to create nesting space. The damage is real but accrues slowly over years, not overnight, so a carpenter-ant sighting isn't cause for panic — it's a reason to have the structure inspected and any moisture problems addressed before galleries expand.

Should I spray the ants I see?

Generally no, especially for carpenter ants. Spraying the visible foraging workers rarely reaches the nest itself, since most of the colony stays hidden inside wall voids or outdoor structures. Baiting, which workers carry back to feed the colony, combined with correcting the moisture problems that attract carpenter ants in the first place, is far more effective. Indoor spraying is generally discouraged because it can scatter a colony rather than eliminate it.

When is the best time to treat for ants?

Early spring, roughly April through May, is the best window. Colonies are just becoming active and haven't reached peak summer size yet, and carpenter ants are most likely to readily accept bait during this period before foraging ramps up. A spring treatment paired with a late-spring follow-up perimeter application suits homes with recurring pressure, catching the population early before it expands into the full summer foraging peak.

Are ants active at night?

It depends on the species and season. Carpenter-ant workers are largely nocturnal foragers in summer, searching for food between sunset and midnight and ranging up to about 100 yards from the nest. Most other NH ant species follow the general daytime temperature-driven activity pattern rather than a strict nocturnal schedule. Across all species, the overriding driver of activity is the ~50°F floor — warmth, not the clock, decides whether ants are moving at all.

Daniel Brady · NH-Licensed Pesticide Applicator · License #782664

|Reviewed by Daniel Brady

When Do Ants Come Out? NH Ant Season Timing Guide

Year-Round & Spring

Ants come out for the season once daytime highs consistently clear ~50°F — the standard insect-activity floor — which southern New Hampshire reaches in early-to-mid April. Activity builds through May, peaks in the 75–95°F heat of June through August, and tapers through September and October as highs fall back toward that 50°F threshold, largely ending by late November. Carpenter ants swarm roughly March through June; winged swarmers found indoors in that window signal an established nest inside the home, not just outdoor foraging.

At a glance

Emergence threshold: ~50°FColonies resume foraging and egg-laying above ~50°F, the standard insect-activity floor (UMass Extension)
NH spring crossing: Early–mid AprilConcord avg. high climbs 44°F (Mar) → 58°F (Apr); Nashua 45°F → 59°F (NOAA/NCEI 1991–2020 normals)
Summer peak range: 75–95°F (Jun–Aug)Ants are most active in this range, matching NH's summer heat (ant-biology sources)
Carpenter-ant swarm window: ~March–JuneSwarmers found INDOORS mean a nest is already inside the structure (UNH Extension; UMN Extension)

Emergence threshold
~50°F
Colonies resume foraging and egg-laying above ~50°F, the standard insect-activity floor (UMass Extension)
NH spring crossing
Early–mid April
Concord avg. high climbs 44°F (Mar) → 58°F (Apr); Nashua 45°F → 59°F (NOAA/NCEI 1991–2020 normals)
Summer peak range
75–95°F (Jun–Aug)
Ants are most active in this range, matching NH's summer heat (ant-biology sources)
Carpenter-ant swarm window
~March–June
Swarmers found INDOORS mean a nest is already inside the structure (UNH Extension; UMN Extension)

The timing answer

The short of it

The verdict · year-round & spring

Peaks late spring–summer; wakes at ~50°F

Ants come out in southern NH when daytime highs pass ~50°F — early-to-mid April — and stay active through about November, peaking in the summer heat.

NH activity calendar

When are they active — the whole year at a glance

Ant activity in New Hampshire tracks outdoor temperature closely: colonies wake once highs pass ~50°F in spring and go dormant again once highs fall back below that mark in late fall.

12-month activity · New Hampshire

Peak · Jun, Jul, AugYou are here · Aug

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

PeakActiveBuildingDecliningDormantCurrent season · Summer

Best window to act · Early spring (April–May) — before colonies expand and while carpenter ants are most likely to take baits; a twice-yearly perimeter/bait program suits homes with recurring pressure.

What else peaks thenJun Jul Aug

Peak months track NH's summer heat (75–85°F highs, June–August); the fall taper is anchored to Manchester's first hard frost (~Oct 19, 50% probability — NOAA 1991–2020).

Season by season

A year in the life

Ant behavior in New Hampshire is driven almost entirely by temperature, with one major exception: a carpenter-ant nest already inside a heated wall doesn't fully go dormant.

01
Spring
The wake-up season. As highs cross ~50°F in April, colonies resume foraging and carpenter ants swarm from roughly March through June. Early workers seek water indoors in kitchens and bathrooms. Winged swarmers appearing indoors during this window is the key infestation signal — it means the nest is inside the structure, not outside.
02
Summer
Peak season. NH's June–August warmth (75–85°F highs) drives maximum activity. Pavement ants and odorous house ants are at their worst indoors during these warm months, and carpenter-ant workers forage at night, sometimes ranging up to 100 yards from the nest.
03
Fall
Activity declines as temperatures drop. Colonies forage heavily in September to build fat reserves for winter, which can produce a brief uptick in sightings before cold weather shuts activity down by November.
04
Winter
Outdoor colonies are dormant, in diapause below the frost line. Indoors, a carpenter-ant nest tucked into a heated wall void can stay active; sightings of large black ants on a warm winter day point to a nest already established inside the home.

New Hampshire context

Ant season in southern New Hampshire

Southern NH towns like Manchester, Nashua, and Concord cross the ~50°F insect-activity floor in early-to-mid April as average daily highs jump from the low-to-mid 40s in March into the high 50s in April. That temperature swing is the real start of ant season, not a fixed calendar date, so an early or late spring shifts the timeline by a week or two. Carpenter ants — the largest and most damaging ants in the region — swarm within that same window, and swarmers found indoors are the clearest sign a colony has already established itself inside a home.

Key local data

Concord's average daily high rises from 44°F in March to 58°F in April, and Manchester's first hard frost falls around October 19 (50% probability) — NOAA/NCEI 1991–2020 climate normals.

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Southern New Hampshire

When to act

Timing your treatment

Acting in early spring beats peak-season foraging and lines up with the window when carpenter ants most readily take bait.

The right window

Early spring (April–May) — before colonies expand and while carpenter ants are most likely to take baits; a twice-yearly perimeter/bait program suits homes with recurring pressure.

Winged swarmers seen indoors

Frass (sawdust-like) piles or rustling sounds inside walls

Large numbers of big black ants indoors

DIY baits fail or ants return year after year

Soft or visibly damaged structural wood

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Learn more about this pest

Common Questions

Frequently asked

Sources & references

UNH Extension — Carpenter Ants fact sheet
carpenter-ant swarm timing, winter indoor sighting = established nest
UMN Extension — Carpenter Ants
indoor swarmers indicate an interior nest
NC State Extension — Biology and Control of Carpenter Ants
mature colony size, annual swarmer production
NOAA/NCEI 1991–2020 Climate Normals (via Current Results, NH April)
Concord/Nashua March–April average high temperatures
NOAA/NCEI 1991–2020 Climate Normals (via Current Results, NH May)
Concord May average high temperature
Penn State Extension — Pavement Ant
pavement-ant seasonal activity
UMass Extension — Growing Degree Days for Management of Insect Pests
~50°F insect-activity floor for the Northeast
Colonial Pest Control — Spring and Early Summer Swarms
New England carpenter-ant swarm timing

Editorial disclaimer: This content is provided for informational purposes only and does not constitute pest control advice. Every property is unique — consult a licensed professional for guidance specific to your situation. Anchor Pest Services is licensed in New Hampshire (#782664).

Written & reviewed by

Verified

Daniel Brady

NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)

Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.

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Last updated Jul 2026

Anchor Pest Services

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Keep Exploring

When Do Ants Come Out? NH Ant Season Timing Guide

The short of it

When are they active — the whole year at a glance

A year in the life

Spring

Summer

Fall

Winter

Ant season in southern New Hampshire

Timing your treatment

Frequently asked

Sources & references

Whatever the season — we handle the timing for you.

Your next step

Ant Season in New Hampshire: Month-by-Month Calendar for Manchester, Bedford, and Nashua

Ant Prevention: Moisture Control Stops NH's Top Pest

How to Get Rid of Carpenter Ants

Where Do Ants Go In The Winter?