Field ants

What field ants look like

Field ants are the ants behind the soil mounds in a lawn. They are large for a yard ant, 3 to 9.5 mm long, and come in red, brown, black or a red and black combination, which leads many people to call them carpenter ants. The difference is the profile of the back. Seen from the side, a carpenter ant has a smooth, evenly rounded thorax, while a field ant has an uneven thorax with a clear dip in the middle. Field ants also have a single node on the waist and a circle of hairs at the tip of the abdomen. They build low mounds of loose soil and thatch in open sunny areas, sometimes 30 cm or more across, usually well away from paving.

Signs you have field ants

• Soil mounds in the lawn. Low domes of fine soil and grass debris in sunny open ground, garden beds and along fence lines.
• Large ants on patios and walkways. Big, fast ants foraging in the open during the day, often mistaken for carpenter ants.
• Ants on shrubs and trees. Steady traffic up and down trunks and stems, where they are tending aphids for honeydew.
• Occasional wanderers indoors. Single large ants turning up near doors and windows, rather than an organised trail in the kitchen.
• Defensive behaviour. Disturb a mound and workers pour out, bite, and spray formic acid that stings on broken skin.

Why field ants come indoors

Field ants are an outdoor nuisance, not an indoor pest. They nest in soil in the open yard and feed mainly on honeydew from aphids plus other insects. They do not nest inside buildings and they do not damage structural wood. What you see indoors is almost always a stray forager that came in through an open door, a torn screen or a gap at a threshold, or a winged ant that swarmed nearby. The real complaints are outdoor ones: mounds that interfere with mowing, ants on a patio or play area, and painful bites when a mound is disturbed. If you have a persistent trail working a kitchen day after day, it is worth checking the identification, because that behaviour points to another species.

How to keep field ants out

• Keep the lawn mowed and thatch under control, since mounds build up fastest in neglected turf.
• Repair door sweeps and window screens so strays cannot walk in.
• Manage aphids on shrubs, hedges and fruit trees to reduce the honeydew that supports large colonies.
• Remove stones, boards and debris sitting on soil in the yard, which give colonies a sheltered start.
• Leave a clear strip of gravel or bare soil between garden beds and the foundation, and keep mulch shallow.

How GO! Pest Control treats field ants

• Inspection. We confirm it is a field ant and not a carpenter ant, map the mounds in the yard, and check which trees and shrubs are supporting them.
• Treatment. We treat mounds directly and use exterior baiting where foraging trails are established, concentrating on the areas your household actually uses.
• Follow-up. We return to check for new mounds, since untreated colonies nearby will move in to fill the space.
• Advice. We explain what is realistic. Clearing every ant from a yard is not the goal. Removing mounds from lawns, patios and play areas is.

We are licensed, insured and bonded, and we work in homes, apartments, condos and businesses across the Toronto GTA, Ottawa and Hamilton.

Common questions about field ants