In New Hampshire, the common 'black ants' homeowners see are pavement ants (2.5–4 mm), odorous house ants (2.4–3.3 mm), Formica field ants (5–8 mm), and carpenter ants (6–13 mm). Carpenter ants are the only structurally damaging species. Resolve the ID with three quick tests: (1) Size — anything under 5 mm is not a carpenter ant. (2) Crush odor — rotten coconut smell = odorous house ant, not carpenter ant. (3) Thorax profile in lateral view — single smooth arch = carpenter ant or possible Formica; two distinct humps with a notch = Formica only. Treatment differs entirely by species, so getting the ID right matters for both cost and outcome.
At a Glance
Camponotus pennsylvanicus (De Geer, 1773) — Black Carpenter Ant
6–13 mm
Minor workers (6–9 mm) are about one-third the width of a US dime; major workers (10–13 mm) nearly half a dime — noticeably larger than any of the common small black ants
Uniformly matte black; dense pale-yellow appressed pubescence on gaster creates faint sheen in direct light
6–13mm
Carpenter ant worker (vs 2.5–4 mm pavement)
5 species
NH Camponotus species (correct count)
$250–500
Carpenter ant vs $110–200 general ant treatment
8–23×
Cost multiplier of untreated Year-1 infestation by Year 5
The most common misidentification calls in NH: homeowners see a dark ant trail and call it 'black ants,' not knowing that 'black ant' covers four species with completely different biology, damage potential, and treatment approaches. This table resolves the most common comparisons.
Subject A
Camponotus pennsylvanicus
Bottom line — Size alone resolves carpenter ant vs pavement ant instantly: anything under 5 mm is not a carpenter ant. If the ant is under 5 mm, the urgency drops dramatically and DIY treatment is usually appropriate.
Bottom line — The three-test ID sequence — size, crush odor, thorax profile — takes 30 seconds and determines whether you are facing a nuisance requiring DIY bait, a structural pest requiring professional treatment, or a field ant requiring no treatment at all. Getting it right at first sighting is the difference between a $200 resolution and a $4,000+ structural repair.
Three quick tests identify which 'black ant' you are seeing and route you to the right response.
The five NH ant species most commonly described as 'black ants.' Each has a unique diagnostic feature, different damage potential, and a different treatment approach.
Species 1
Camponotus pennsylvanicus
Distinguishing feature
The only NH 'black ant' that excavates structural wood. Single smooth thorax curve, single-node petiole, polymorphic size (trail contains multiple ant sizes). NH's #1 structural pest per UNH Extension. Urgency: 5/5.
Species 2
Tetramorium immigrans
Distinguishing feature
Two petiolar nodes (unique to Myrmicinae), parallel ridges (rugae) on head and thorax, pair of propodeal spines. Famous for territorial 'sidewalk wars' between colonies in spring. No structural damage. Urgency: 2/5.
Species 3
Tapinoma sessile
Distinguishing feature
Rotten-coconut/blue-cheese odor when crushed — the diagnostic. Single petiolar node hidden beneath gaster. Polydomous supercolonies in urban NH. CRITICAL: sprays trigger colony budding. Bait-only treatment required. Urgency: 3/5 nuisance.
Species 4
Formica subsericea
Distinguishing feature
Two-hump notched thorax in lateral profile is the gold standard separator from carpenter ants. Diurnal forager. Sprays formic acid defensively. No structural damage. Urgency: 1–2/5 outdoor nuisance.
Species 5
Crematogaster cerasi
Distinguishing feature
Heart-shaped gaster raised over thorax in alarm posture (the 'acrobat' behavior). Often found in old carpenter ant galleries — if acrobat ants are present, carpenter ants may have been too. No primary structural damage but indicator of moisture problems. Urgency: 3/5.
Carpenter ant pressure in NH varies by county and housing stock age. The five service counties each have distinct ant species pressure profiles.
Highest carpenter ant case volume in NH. Manchester's older balloon-frame housing and Nashua's pre-1960 stock carry elevated structural risk. OHA is also a dominant urban complaint species in dense neighborhoods. Pavement ants dominate paved suburban areas throughout the county.
Carpenter ant pressure is extreme for coastal and lakefront properties; HIGH in Salem, Derry, and Londonderry. Formica field ants are widespread in the suburban lawn environment and frequently cause misidentification calls during their spring sidewalk-war displays.
Concord's older downtown housing supports carpenter ant satellite nest activity. OHA is documented in Merrimack River valley homes with wall-void moisture. Pavement ants are abundant along Concord's downtown sidewalk corridors.
Dover and Rochester mill-era housing shows elevated carpenter ant incidence. Acrobat ants are commonly found in homes with EIFS or polystyrene insulation — often in old carpenter ant galleries from prior infestations.
27.3% of homes built before 1940 — the oldest stock of the five service counties — combined with the Monadnock region's heavy forest cover produces high per-home carpenter ant pressure. Field ants are abundant in rural lawn and field-edge settings.
Bottom line — The ID test that matters most in NH: if the ant is over 5 mm, take a lateral profile photo to confirm single-curve (carpenter ant) vs two-hump thorax (Formica). Everything under 5 mm resolves to a non-structural species with lower urgency.
Each image is calibrated to show the single most diagnostic feature for that species. The size comparison in this grid resolves most identification questions instantly.
Lateral profile showing the defining feature: a single evenly rounded arch from front to rear of the thorax with no breaks, notches, or spines. Size 6–13 mm — the largest ant in this comparison. This is the ant that requires structural treatment when found indoors.
Viewed from above, the parallel ridges (rugae) running the length of the head capsule and thorax are visible to the naked eye on pavement ants under good lighting. Two petiolar nodes are visible from the side. Workers are 2.5–4 mm — one-third to one-half the size of a carpenter ant minor.
The OHA's single petiolar node is flattened and concealed beneath the first gastral segment — making the gaster appear to sit directly on the thorax in lateral view. Workers are 2.4–3.3 mm. The rotten-coconut crush test is the fastest ID. Critical treatment note: spraying OHA triggers colony budding.
The definitive lateral view of Formica subsericea showing the two-hump thorax: a taller anterior hump (promesonotal section) and a clearly lower posterior section (propodeum) with a visible depression between them. Size 5–8 mm overlaps carpenter ant minors, making this the most frequently confused pair. Thorax outline resolves it.
A branching ID guide that routes each 'black ant' sighting to a species diagnosis and treatment recommendation.
Address moisture defects before any ant infestation escalates — carpenter ants require >15% wood moisture content for colony founding; eliminating roof leaks, gutter overflows, and plumbing drips removes the primary attractant.
Use the three quick tests before purchasing any treatment: (1) size against a coin, (2) crush odor, (3) thorax profile photo — matching the ant to the correct species prevents the wrong product from making the problem worse (especially for OHA, where sprays trigger budding).
Apply only non-repellent baits for odorous house ants and pharaoh ants — contact pyrethroid sprays cause colony fission into new satellite nests, converting a single-room problem into a whole-house problem within days.
Seal foundation cracks, utility penetrations, and window frame gaps with silicone caulk to block all species of foraging ants, regardless of species — exclusion is effective against all of them simultaneously.
Store firewood at least 20 feet from the foundation, elevated off the ground — firewood provides harborage for carpenter ant parent colonies and under-stack conditions for pavement and field ant soil nests.
Schedule an annual perimeter inspection in April before the May–June swarm window — catching a newly founded carpenter ant colony in Year 1 costs $250–$600 versus $4,000–$11,500+ if discovered at Year 5 (NH 2026 cost-of-delay data).
New Hampshire's 84% forest cover, aging housing stock (median build year 1982, ~22% pre-1950), and humid continental climate sustain the full range of eastern US ant species. Carpenter ants thrive in the moisture-damaged wood of older homes; odorous house ants exploit the polydomous niche of suburban landscape mulch and wall voids; pavement ants dominate the dense pavement footprint of Manchester, Nashua, and Portsmouth; field ants populate the lawn-forest edges of every county. This species diversity means a homeowner in Hillsborough County could plausibly encounter all four in the same yard within a single season.
Key Local Data
Nationally, carpenter ants are the most-treated ant species by professional PMPs at 66%, followed by odorous house ants at 62% and pavement ants at 59% — a ranking that matches NH operator complaint data almost exactly (NPMA Hansen 2012).
Anchor Pest Services provides free carpenter ant inspections and ant species identification across Manchester, Nashua, Bedford, Derry, and surrounding southern NH communities. No guessing, no wrong treatment.