The single most useful thing to know about ants is that the trail across your worktop is not the colony. It is the delivery service.
Foragers are a small and entirely replaceable fraction of the population. The queen and the brood are somewhere you cannot see, and every treatment decision follows from that one fact — including why the spray under your sink makes the situation worse rather than better.
The three nuisance ants you actually have
Washington has plenty of ant species. Three of them account for nearly every non-structural callout, and telling them apart takes about ten seconds.
| Species | Where and when | How to know |
|---|---|---|
| Odorous house ant | Dominant indoor ant west of the Cascades. Kitchens, bathrooms, wall voids near plumbing. Peaks through the wet spring. | About an eighth of an inch, dark brown to black, fast-moving in defined trails. Crush one: a sweet rancid smell, usually described as rotten coconut. |
| Pavement ant | Driveway seams, patio slabs, foundation edges, and indoors on slab-on-grade construction. Common statewide, more so east. | Similar size, brown to black, with fine parallel grooves on the head and thorax. Small mounds of excavated soil pushed up through cracks in concrete. |
| Thatching ant | Outdoors, in large thatch mounds of conifer needles and twigs. Rural and wooded properties on both sides of the state. | Large, red and black, and they bite and spray formic acid when disturbed. A yard problem rather than a house problem, and a beneficial predator you may not want removed. |
Why the spray under the sink makes it worse
Retail contact sprays do three things, and only the first is the one you wanted.
They kill the foragers on the trail, which the colony replaces within days. They leave a repellent residue, so the colony reroutes around the treated area and reappears somewhere else in the house. And with odorous house ants specifically, they can trigger budding — a stressed colony splitting into multiple satellite nests, each with its own egg-laying queen.
The visible outcome is the one people describe on the phone constantly: one trail in the kitchen became three trails in three rooms two weeks after treating it themselves.
How a professional ant job actually runs
A competent Washington ant treatment has four parts, and the first is not chemical.
Identification. Species determines bait choice, because ants shift between sugar-feeding and protein-feeding across the season and a bait matrix they are not currently interested in gets ignored. A technician who does not name the species is guessing.
Tracing the trail to the entry point. The trail leads somewhere, and following it to the pipe penetration, window frame gap or siding joint tells you where the exterior treatment and the sealing work need to go.
Baiting. Slow-acting bait placed on the trail, not sprayed across it. Foragers carry it into the nest and share it by trophallaxis, which is how the active ingredient reaches the brood and the queen. Expect more ants for two or three days. That is the bait working.
Exterior perimeter and exclusion. A non-repellent exterior treatment plus sealing the entry points, so the next colony along does not simply take the vacancy. On a property with an annual problem, this is the part that a quarterly plan is genuinely buying.
What to do — and stop doing — while bait is down
Stop spraying anything, including household cleaners, along the trail. Repellents interrupt the delivery route and undo the treatment. Wipe up spills away from the trail, keep sugar, honey and pet food sealed or elevated, and empty recycling that has held sweet residue — you are removing competition for the bait rather than starving the colony.
Then seal what you can reach: gaps around pipe and cable penetrations, failed caulk at window and door frames, and the joint where siding meets a slab or deck. Ants come in through openings measured in fractions of a millimetre, so this is never complete, but it changes the pressure.
What ant control costs in Washington
A one-off nuisance ant callout runs $150 to $350 in 2026 and usually includes one follow-up visit. Quarterly plans run $100 to $175 per visit and earn their cost on a property with an annual spring problem, because most of the value is in exterior perimeter work done before the ants get in.
Carpenter and moisture ant work is quoted higher, $250 to $600, because the job is locating a nest inside a structure rather than intercepting a trail. The statewide pest control page carries the full cost table across all eight services.