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Types of Ants Found in Ontario – From Carpenter to Pavement Ants

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Ant Library

Carpenter Ant 

Appearance: Large ants (6–13 mm), usually black or dark brown. Workers vary in size; winged reproductives appear in spring.

Habitat: Nests in damp or decaying wood—inside walls, attics, decks, or trees. Does not eat wood but excavates it to create galleries.

Behaviour: Active mostly at night. Trails may be seen along baseboards or between buildings and trees.

Risk to Humans: Does not sting but can bite. Known to cause structural damage over time if left untreated.

Interesting Fact: One of the most common indoor ant species in Ontario, especially in cottages and wooded properties.

Pavement Ant

Appearance: Small (2.5–4 mm), dark brown to black with parallel grooves on the head and thorax.

Habitat: Nests in cracks in pavement, sidewalks, foundations, and walls. May also nest under stones or floors.

Behaviour: Attracted to sweets and greasy foods. May enter buildings in large numbers during warm months.

Risk to Humans: Does not pose a health threat but can become a persistent nuisance.

Interesting Fact: Often seen battling other colonies on sidewalks in early summer.

Odorous House Ant 

Appearance: Small (2.5–3 mm), brown or black. Emits a strong, rotten coconut-like odor when crushed.

Habitat: Nests in wall voids, under floors, or in moist areas. Outdoors, nests may be found under mulch, stones, or woodpiles.

Behaviour: Forms large colonies with multiple queens. Frequently invades kitchens and pantries.

Risk to Humans: Harmless but difficult to control due to their colony size and nesting habits.

Interesting Fact: Known for relocating nests frequently, especially after treatments or disruptions.

Pharaoh Ant

Appearance: Tiny (1.5–2 mm), pale yellow to reddish with a darker abdomen.
Habitat: Prefers warm, humid indoor environments like kitchens, wall voids, hospitals, and apartment buildings.

Behaviour: Builds many small colonies connected by trails. Extremely difficult to eliminate without professional ant control.

Risk to Humans: Can contaminate food and surfaces, especially in medical or commercial settings.

Interesting Fact: Colonies can “bud” into multiple new colonies when disturbed, making DIY treatments ineffective.

Field Ant

Appearance: Medium to large (4–8 mm), black, red, or black and red ants with a single waist node.
Habitat: Nests in soil, logs, tree roots, and grassy yards—especially in rural and suburban Ontario.

Behaviour: Does not typically nest indoors but can enter homes in search of food. Active from early spring to fall.

Risk to Humans: Generally harmless but can become a nuisance near foundations and walkways.

Interesting Fact: Sometimes mistaken for carpenter ants but do not cause structural damage.

Thief Ant

Appearance: Very small (1.5–2.2 mm), pale yellow to light brown. Often mistaken for pharaoh ants.
Habitat: Nests in wall voids, under flooring, behind baseboards, and in cracks of structures.

Behaviour: Steals food and brood from other ant colonies. Attracted to grease, protein, and sweets.

Risk to Humans: Hard to detect and treat due to their size and nesting habits. May contaminate food.

Interesting Fact: Often goes unnoticed until a large indoor infestation develops.

European Fire Ant

Appearance: Reddish-brown, 4–5 mm long, with a distinctive stinger and aggressive behavior.
Habitat: Moist shaded areas—lawns, garden beds, compost piles, and under stones. Increasingly found in residential yards across southern Ontario.

Behaviour: Extremely territorial. Swarms aggressively when disturbed. Can deliver a painful sting.

Risk to Humans: Risk of painful stings, especially in lawns, parks, or cottage areas. Known to displace native ants.

Interesting Fact: Invasive species from Europe; colonies can grow very large with multiple queens.

Acrobat Ant

Appearance: Small (2.5–3 mm), light brown to black. Heart-shaped abdomen is often raised over the body when disturbed.
Habitat: Nests in wood, foam insulation, or wall voids. Outdoors in logs, tree bark, and old carpenter ant tunnels.

Behaviour: Forages inside for sweets and proteins. Colonies can relocate quickly if disturbed.

Risk to Humans: May bite or release an unpleasant odor. Not destructive but can be persistent.

Interesting Fact: Named for their habit of raising their abdomen like an acrobat when threatened.

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