Large yellow ants

What large yellow ants look like

Large yellow ants are unusual in that most people meet them only once a year, as a sudden indoor swarm. Workers are 3 to 5 mm long and a distinct orange-yellow to yellowish-brown, much paler than other ants of that size. The swarmers are larger, darker and winged, and they are the ones that appear at basement windows. If you crush a worker you get a clear lemon or citronella smell, which is why they are also called citronella ants. The body is smooth with a single node on the waist and a ring of fine hairs around the tip of the abdomen. The colour alone separates them from field ants, pavement ants and carpenter ants.

Signs you have large yellow ants

• Sudden indoor swarms. Dozens or hundreds of winged ants appearing at a basement window or a crack in a slab, often in spring or late summer.
• A lemon smell. Crushed ants give off a citronella or lemon odour that is noticeable even from a small number of ants.
• Yellow soil piles. Loose granular soil pushed out along the foundation, under patio slabs, or at the edge of a basement floor crack.
• Ants under objects outdoors. Lifting a stone, log or board near the house reveals a mass of pale yellow ants and brood.
• Little or no kitchen activity. Unlike most house ants, you almost never find them on counters or in food.

Why large yellow ants come indoors

These ants are mainly an outdoor nuisance rather than a serious indoor pest. They live underground and feed almost entirely on honeydew produced by aphids and mealybugs that feed on roots, so they have no reason to forage in your kitchen. The problem is location. When a colony nests against a foundation, under a slab, in a crawl space wall or beside a basement floor crack, the annual swarm exits through the nearest opening, and indoors is sometimes the nearest opening. Occasional workers wander inside through the same gaps. They do not damage wood, they do not contaminate food in any meaningful way, and they do not establish long-term colonies inside a heated building.

How to keep large yellow ants out

• Seal cracks in basement floors and walls, especially at the cove joint where the floor meets the wall.
• Caulk around basement window frames, utility penetrations, sump covers and floor drains.
• Improve drainage so soil next to the foundation is not constantly wet, since they favour damp ground.
• Remove stones, boards, landscape timbers and rotting logs lying on soil close to the house.
• Keep an eye on the same spot each spring, because a colony that swarmed once will usually swarm there again.

How GO! Pest Control treats large yellow ants

• Inspection. We confirm the species, locate the swarm exit point, and trace the nest outdoors along the foundation, under slabs or in the crawl space.
• Treatment. Because these ants rarely forage indoors, baiting is often ineffective. We focus on direct nest treatment and a targeted exterior application around the foundation and entry points.
• Follow-up. We check the exit point after treatment and can schedule a visit ahead of the next swarming season if the nest is in an awkward spot.
• Advice. We show you which cracks to seal so the next swarm goes outside rather than into the basement.

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 large yellow ants