Most people watch where ants are going — toward the food source. But the information you need is where they're coming from. The trail leads from the nest to the food. Follow it in reverse — from the food source back along the trail to the wall, crack, or ground entry point — and you've found the colony's access route.
Pavement ants: Small sandy mounds pushing up through sidewalk cracks, driveway expansion joints, and patio edges. The mound is directly above the nest.
Fire ants: Dome-shaped mounds with no visible entrance hole on top (they enter from below). Mounds can be 18 inches tall in mature colonies. Never disturb by kicking — use the Texas Two-Step method.
Carpenter ants: No visible mound — they nest inside wood. Look for frass (fine sawdust with insect body parts) ejected from the nest opening. Follow the trail to a tree stump, fence post, landscape timber, or — worst case — structural wood in your home. Tap suspected wood with a screwdriver and listen for a hollow sound or rustling.
Argentine ants: Shallow nests in mulch, under rocks, landscape stones, and potted plants. Supercolonies can stretch across entire properties — there may not be one nest but dozens of satellite colonies connected by trails.
When the trail disappears into a wall through a crack, gap around a pipe, or electrical outlet, the nest is either inside the wall void or the ants are traveling through the wall to an exterior colony.
To determine which: Place a bait station at the wall entry point. If ants are carrying bait inward (into the wall) and not returning with it outward, the nest is likely inside the wall. If traffic is bidirectional — ants going in AND coming out with bait — the nest is probably outside and ants are using the wall as a highway.
Wall void nests are common for: Odorous house ants (often nest in wall voids near moisture sources), carpenter ants (nest in moisture-damaged wood inside walls), and pharaoh ants (nest in warm wall voids near hot water pipes).
Ants come back because treatments target workers, not the queen. Finding the nest — or at minimum, the entry point nearest the nest — lets you place bait where workers will carry it directly to the queen. Bait at the entry point is 10x more effective than bait on the kitchen counter because it's on the direct route to the colony.