Black Field Ant

The black ant: general information

The black field ant (Formica subsericea and related Formica species) is one of the most widespread ants in Quebec. It's found in meadows, fields, boreal forests, sandy environments and peat bogs, but also around homes, along sidewalks and in lawns. Unlike the carpenter ant, it doesn't excavate structural wood: it nests in soil, under stones and slabs, and enters homes mainly to forage.

Physical description

Its colour ranges from black to silvery grey or dark brown depending on species. Its body is thin and slender, clearly less robust than the carpenter ant's. Approximate sizes:

• Workers: 4.5 to 7 mm
• Males: 7 to 8 mm (permanently winged)
• Queens: 8 to 13 mm, with a more massive body; winged when young, they shed their wings after mating

Lifestyle, biology and reproduction

• Lifespan: males a few days, workers a few weeks to a few months, queens 10 to 25 years.
• Development from egg to adult in about 3 to 5 weeks; each stage (egg, larva, pupa) occupies a dedicated nest chamber.
• Nuptial flight in late spring; egg-laying begins in early summer. After mating, the queen sheds her wings and founds a colony.
• Important trait: these colonies are often polygynous — a single nest can house several queens, making the colony more resilient and harder to eradicate.

Diet and aphid "farming"

The black ant feeds on live or dead arthropods, aphid/scale honeydew, tree sap and nectar. Notable behaviour: it "farms" aphids on garden plants to harvest their sweet honeydew. That's why a black-ant infestation often goes hand in hand with aphids — treating one helps control the other.

Signs of presence at home

• Worker trails on surfaces, counters and baseboards
• Dirt or sand mounds in the lawn, between slabs or along foundations
• Aphid colonies on garden plants
• Food invasion, especially sweet and greasy items
• Larvae, workers, pupae or eggs visible under stones and pots

Black ant or carpenter ant?

They're confused, but the distinction changes the treatment:

• The black field ant has a thin slender body, nests in soil and doesn't attack structural wood. Its bite is mild.
• The carpenter ant is noticeably larger and more robust, and excavates wood (structural risk). See our carpenter ant page.

When in doubt, a professional identification avoids an unsuitable treatment.

Our professional method

Polygynous colonies (multiple queens) often resist home remedies. Our approach:

• Inspection to locate the nest(s) (soil, slabs, walls) and entry points.
• Targeted baits carried by workers back to the queens — essential when there are several.
• Residual treatment at the perimeter and entry points (takes time; a follow-up visit may be needed).
• Aphid control and exclusion recommendations (sealing, moisture, slab cracks).
• Written guarantee, Health Canada approved products, CD5-certified technicians.