Ants Coming Out of Wall Cracks: Where Are They Nesting?

A steady stream of ants emerging from a hairline crack in the wall is a common and annoying sight. The crack is only an exit. Somewhere behind it, in the wall cavity, behind the plaster or outside, there is a nest or a trail leading to one.

This guide explains what it means and how to deal with it.

The short answer

Ants coming from wall cracks use the crack as a doorway between a nest and a food source. The nest may be inside the wall void, behind tiles or skirting, in the floor, in a nearby plant pot or soil, or outside the building, with the ants entering through gaps and following paths along pipes and wires. Locating the nest means following the trail, watching direction and activity, and checking nearby moisture and wood. Treat with baits that workers carry to the colony rather than spraying the crack, then seal the crack once activity stops. Persistent cases may need a professional.

Where nests may be

1. Inside wall cavities: Especially in damp or hollow walls.
2. Behind tiles and skirting: Warm, sheltered voids.
3. In the floor or slab: Cracks and gaps beneath.
4. Outdoors: In soil near the foundation, garden beds or planters.
5. In wood: Door frames, window frames and furniture, for carpenter ants.
6. Near moisture: Leaks and damp patches.

How to work out the direction

• Watch the trail at different times of day. Which way are ants carrying food, and which way do they come from?
• Look for the crack where the most ants enter or leave.
• Check the other side of the wall, outside or in the next room.
• Look for damp patches, hollow-sounding wood and sawdust-like debris.

What to do

1. Do not just spray the crack: It kills the ants you see, but not the nest, and may scatter the colony.
2. Use bait: Place ant gel bait near, not in, the crack, out of reach of children and pets, and let the workers carry it back.
3. Remove attractants: Clean food and sweet residues, and fix leaks.
4. Seal after control: Once the ants have stopped coming, seal cracks with suitable sealant or filler.
5. Treat the outside: If the nest is outdoors, treat the perimeter or nest area.

If wood is involved

Sawdust-like material (frass) near cracks and frames may indicate carpenter ants. They need professional assessment, since they can damage wood.

Prevention

• Repair wall cracks and damp.
• Keep plants and mulch away from walls.
• Seal gaps around pipes and windows.
• Manage food and waste.

When to call a professional

If ants keep returning, a professional can find and treat hidden nests in walls.

Frequently asked questions

Why do ants come from the same crack?

It is their trail between nest and food.

Should I fill the crack right away?

Treat the colony first, then seal. Otherwise ants may find another way.

Are wall nests dangerous?

Mostly a nuisance, but some species damage wood or wiring.

Will chalk help?

It is unreliable. See our guide on chalk and powders.

This guide is part of IPest's complete resource on ant control. For identification help, prevention and treatment options, see our full ant control guide for Bangalore.