Pick the Right Time
Ants forage when they are warm. A cool morning shows you very little; a sunny afternoon from late spring through summer shows you the whole operation, with workers moving steadily in both directions. After rain, when the ground is drying and warming, can be good too.
Give it twenty or thirty quiet minutes rather than a glance. Resist the urge to spray or wipe the trail before you start. It is the only map you have.
Read the Trail
A trail has two ends: the food and the nest. The food end is obvious. To find the other, watch the ants that are walking away from the food, not towards it. Workers heading home often carry something, a crumb or a swollen abdomen full of liquid, and they move with purpose.
- Follow, do not chase. Keep a little distance and let them lead. Ants use edges, so check skirting, the join between wall and floor, pipe runs and window frames.
- Note where it leaves the room. A gap under a door, a crack in a threshold, a hole round a pipe. That is an entry point, and the nest is somewhere beyond it.
- Pick it up outside. Go to the matching spot on the outside wall and look for the same traffic at ground level.
- Expect more than one trail. A big colony can run several routes, and two trails can come from two nests.
For a room-by-room walk from the kitchen to the garden, see following the trail back on your own property.
Clues Outdoors
Black garden ants dig, and the soil has to go somewhere. The tell-tale sign is fine, dry, crumbly soil or sand pushed up where it should not be:
- In the joints between patio slabs or block paving, often as small neat heaps
- At the base of an outside wall, where the path or patio meets the brickwork
- Along the edge of a lawn or in a border beside the house
- Under a stone, a pot or a slab that has sat in the sun
- Round the frame of a patio door or a back step
On a warm day, workers will be going in and out of a small hole near the heap. Lifting a pot or a loose slab carefully often shows the chambers and pale larvae just underneath. Put it back gently once you have looked.
The heap nearest the house is not always the one. Gardens often hold several colonies. Watch which heap the indoor trail actually leads to rather than assuming the closest one is responsible.
Clues That Point Indoors
Sometimes the trail never goes outside. Ants appear through a crack in a solid floor, from behind a skirting board or out of a socket, and nothing can be found in the garden. That usually means a nest under the floor, in a wall base or in a cavity, with the ants surfacing directly into the room.
Signs to note include fine grit or soil appearing along a skirting, ants in the same room in cooler months, and winged ants emerging indoors in summer. A nest like that cannot be reached by looking, and nobody should be lifting floorboards to prove a point. The page on ants in walls and under floors explains what happens then.
When You Cannot Find It
That is common and it is not a failure. The nest may be under a patio, beneath next door's path or deep in a wall. What you have found, the trail, the entry points and any heaps, is still exactly what we need to know. Write it down or take photos, and tell us when you ring.