Why Ants Keep Coming Back After You Spray

Ants come back because the ants you killed were never the problem. The nest sits somewhere else, usually under a slab or inside a wall. University of California IPM puts it bluntly: as few as 1 percent of a colony's foraging workers can bring in enough food to keep the queens and larvae going. Clear a trail and the colony barely registers it.

Which Ant Is Actually On Your Counter?

Two species turn up most often. Ohio State University Extension's factsheet on ants in and around the home names the pavement ant and the odorous house ant as the ants that turn up inside Ohio houses, and it notes that Ohio's species are not the biting and stinging problem that fire ants are further south. That is the good news. The bad news is that both are hard to shift, for different reasons.

The smell test is worth knowing because it settles the identification in a second with no magnifying glass. Crush one odorous house ant and you get a chemical release people describe as rotten coconut or blue cheese. There is a published study on exactly that, reported by the University of Wisconsin insect diagnostic lab: given the choice, about 40 percent of human judges called the smell blue cheese and about 25 percent called it rotten coconut. Either way, if a crushed ant has a smell at all, you are not dealing with a pavement ant.

Why Killing The Ants You See Does Almost Nothing

A contact spray kills the workers it lands on. Those workers are a tiny, replaceable fraction of the colony, and the 1 percent figure from UC IPM is the whole problem in one number: the nest can be supplied by a handful of foragers, so removing the ones on your counter does not starve anything. Meanwhile the queens keep laying, the brood keeps developing, and in a week or two there are foragers on the counter again.

Baits work on the opposite principle. Ants feed each other mouth to mouth, a behavior called trophallaxis, so a worker that carries bait home spreads it through the nest, queens included. That also explains why the bait has to be slow. UC IPM is explicit that a bait which kills workers too quickly never reaches the queens, and the colony recovers. The EPA's own do's and don'ts for pest control put baits first for the same reason, as the low exposure option used after prevention, provided they stay out of reach of children and pets, and it adds that anything not in a bait or trap belongs in targeted spots rather than sprayed over a whole room.

The Spray That Makes The Problem Bigger

Odorous house ants in a town or suburb do not keep one tidy nest with one queen. Utah State University Extension describes urban colonies of this species as polydomous and polygynous, meaning many nests per colony and many queens per nest, and says they reproduce by budding: a queen and a group of workers pick up brood and walk off to start a new subcolony. A colony like that can run to tens of thousands of workers, and a supercolony spread across several properties into the hundreds of thousands.

Utah State also names what triggers budding, and it is not only crowding. Inadequate insecticide applications can split a colony and set new subcolonies forming. So the familiar story, spray the trail, quiet for three days, then ants in two more rooms, is not bad luck or a stubborn ant. It is the colony doing what a disturbance tells it to do. A repellent product applied across a trail can push nests apart faster than any amount of it kills.

Read The Trail Before You Touch It

Ten minutes of watching is worth more than a can of anything. The trail is a line pointing at the nest, and once you spray it you have erased the only directions you had. Work through this before anything gets treated:

• Follow it backwards. Where do they stop coming from a room and start coming from a gap? Baseboard, window frame, under a cabinet, the slab edge in the garage.
• Look for grit you did not put there. Cornell's pavement ant factsheet describes small piles of sand and soil particles appearing in buildings near cracks in concrete slabs or at the top of a foundation wall, where the ants push out what they excavate. That is a nest under your floor, not a visitor.
• Note what they are on. A trail working a juice spill behaves differently from one working grease or pet food, and it changes which bait a technician would put down.
• Check the wet spots. A leaking trap, a sweating pipe, a planter saucer. Ants need water as much as food, and the EPA's guidance starts with removing food, water and shelter before anything chemical.
• Look outside at the same wall. Mulch piled against siding, a landscape timber, pavers right at the foundation. Cornell lists foundations, sidewalks, patios and rocks as standard pavement ant nest sites.
• Write down the time of day. Trails run on a schedule, and a technician who knows when yours is busy can place bait where it will actually be found.

What It Means If You Still Have Ants In October

It usually means the nest is in or against the heated part of the building. Outdoor foraging winds down as the soil cools, so a trail that is still running in a Stark County kitchen in October is being fed by something that is not experiencing October. Cornell describes exactly where that tends to be: it is uncommon for a pavement ant colony to be entirely indoors, but they are found along foundations, in wall voids and in attic insulation, and they reach interior rooms through cracks in foundation walls and interior slabs.

Practically, that makes autumn a better time to deal with ants than it looks. The exterior work that keeps next spring quieter is the same work as everything else on the fall list: pulling mulch back off the siding, clearing the gutters so the foundation is not staying wet, sealing the gaps around pipe and wire penetrations. And if a trail survives the first few cold nights, treat it as a nest in the structure rather than something that will leave on its own.

When It Is Worth Handing Over

Ants are the most common nuisance pest in the country and they are not getting less common. In the National Pest Management Association's ant survey, every pest professional surveyed had treated ant infestations in the past year, and 54 percent said ant infestations were growing. The three species they named as most prevalent are the three in the table above. The same research found 29 percent of Americans have tried a natural or home remedy on ants in their house, which is a lot of ant trails treated before anyone had identified the ant.

The line is simple enough. A single trail to one spill, cleaned up and gone within a day, is a housekeeping event. A trail that comes back after you clean, a trail you can find grit beside, more than one trail in different rooms, or any ant that looks too big to be either of the ants in the table, is a nest problem. Professional ant control starts with identifying the species, because the species decides the plan, then puts slow-acting bait where the trail actually runs rather than where the ants are most visible, treats the exterior where the colony lives, and comes back to confirm the trail is gone instead of just quiet. Ants are also one of the pests covered by State Shield Essential, the quarterly plan built around four visits a year to break egg cycles, and if pests come back between treatments, so do we, at no cost.

State Termite has worked Northeast Ohio out of North Canton since 1933, and we would rather look at the trail than guess at it. If ants keep reappearing in your kitchen, bathroom or basement, see our pest library entry on ants for identification, then get a free estimate or call 330-494-6199.