Mostly baits, and the active ingredient is usually fipronil, hydramethylnon, abamectin or a borate. The bait matters less than the method: it has to be the food that species wants, placed exactly where they already walk, left undisturbed for days, and paired with a non-repellent liquid outside rather than a repellent spray.
The reason a professional treatment works and the can under your sink does not is the same reason in both cases. Spraying kills foragers and repels the rest. As few as 1% of a colony's foragers can feed the whole nest, so the ants you can see are close to irrelevant, and a spray over a bait ruins the bait.
Why the ants you can see barely matter
Start here, because it explains every product choice further down. The University of California's IPM program puts the number bluntly: as few as 1% of a colony's foraging workers can gather enough food to support the queens and larvae sitting in the nest. Everything you watch marching along the counter is a rounding error in a colony that may hold tens of thousands of ants and, in several of our species, more than one queen.
So a product that kills ants on contact solves the visible part of the problem and none of the actual one. Worse, most over-the-counter sprays are repellent. NC State's entomologists describe the failure mode exactly: a repellent spray "doesn't kill the ants but may only 'detour' them to another food source temporarily." You spray the kitchen trail, the trail disappears, and three weeks later the same colony is coming in behind the dishwasher instead.
That is the whole professional logic. Do not try to kill ants. Get the ants to carry something home.
What is actually in the products
There is no secret professional chemical. The active ingredients in a technician's bait are the same ones listed on the back of consumer bait stations; the differences are formulation quality, the range of baits carried, and knowing which one this species will eat this month.
| Active | What it is | Typical form | Notes |
|---|---|---|---|
| Fipronil | Phenylpyrazole; disrupts the ant's nervous system | Gel baits and non-repellent liquids | Also the common non-repellent perimeter active. Slow enough for transfer between ants |
| Hydramethylnon | Stops the ant's cells producing energy | Granular baits, protein baits | The standard fire ant broadcast bait. Degrades in sunlight, so it goes down fresh |
| Abamectin (avermectin) | Derived from a soil bacterium; nerve agent at very low doses | Gels and granules | Used at tiny concentrations, which is what keeps it slow-acting |
| Boric acid / borates | Stomach poison, mineral rather than synthetic | Liquid sugar baits, gels, stations | Must be under 1% active. Stronger kills the forager before she gets home |
That last row is the single most common DIY mistake, and it is worth stating plainly. Homemade borax-and-sugar recipes circulating online are frequently mixed far too strong. UC IPM's figure for a liquid borate bait is 0.5 to 1% borate in sugar water. At higher concentrations the ant dies on the counter, which feels like success and guarantees the colony survives.
One correction to a claim that appears on a lot of pest control pages, including an older version of this one. Piperonyl butoxide is not an ant insecticide. It is a synergist, an additive that blocks an insect's ability to break down a pesticide it has been dosed with, and it shows up mostly in pyrethrin aerosols. It is not what a colony treatment is built on.
Repellent versus non-repellent: the distinction that decides everything
Ask a technician what they are spraying around the outside of your house and the useful answer is not the brand, it is which of these two categories it falls into.
A repellent product is one ants can detect and avoid. Most consumer aerosols and many older perimeter chemistries work this way. They create a line ants will not cross, which sounds ideal and behaves badly: the colony reroutes, and in some species a disturbed colony responds by splitting into satellite nests, so one problem becomes three.
A non-repellent product is undetectable to the ant. She walks through the treated band, picks up a trace on her body, carries it back and passes it to nestmates during grooming and feeding. Fipronil is the common example. Used outside while baits work inside, it reaches ants that never find a bait station.
This is also why the timing advice everyone ignores actually matters. NC State is explicit: do not spray the ants or the baited area, because spraying will contaminate the bait and repel the ants away from it. If a technician baits your kitchen and you wipe the trail with a cleaner that evening, you have undone the visit.
The bait has to match the species, and the season
Ants are not interchangeable. The reason a bait station sits untouched for a week is almost always that it is the wrong food, and food preference shifts through the year as a colony's needs change between raising brood and feeding adults.
| Ant | How to recognise it | What it wants | Where it nests |
|---|---|---|---|
| Odorous house ant Tapinoma sessile | 1/8 inch, dark brown to black, smells like rotten coconut when crushed | Sweets first, sometimes protein | Wall voids, around water pipes and heaters, shallow soil nests outside |
| Argentine ant Linepithema humile | 1/8 inch, dull brown, endless orderly trails | Sugar year-round; protein in spring while brood is being raised | Shallow nests just under the soil surface, mulch, irrigated beds |
| Pavement ant Tetramorium immigrans | 3/16 inch, dark brown to black, two-node waist, soil piles at slab cracks | Sweets, protein and grease | Under slabs, stones and walkways; along foundations |
| Carpenter ant Camponotus spp. | Large, 1/4 to 1/2 inch, black or red and black | Sweets and honeydew | Damp or decayed wood, tree cavities, with satellite nests in wall voids |
| Red imported fire ant Solenopsis invicta | Reddish with a darker abdomen, variable sizes in one nest, stings | Protein and oils, some sweets | Open sunny mounds in disturbed soil; occasionally wall voids |
UC IPM's species guidance gets specific. Odorous house ants and Argentine ants both prefer sweet baits, with borates under 1% listed for each, and both will take protein baits carrying fipronil or hydramethylnon when the colony is raising brood in spring. For Argentine ants there is a counterintuitive instruction worth repeating: bait outdoors and avoid baiting indoors, because an indoor station can pull more ants into the house than it removes.
Argentine ants deserve one regional footnote. The famous "supercolony spanning entire city blocks" finding comes from California and Europe. When Buczkowski, Vargo and Silverman sampled the Carolinas and Georgia specifically, they found colonies under about 0.6 acre that fought each other at the boundaries. Still a multi-queen network that can run across several adjoining properties, which is why a neighbour's untreated yard keeps reseeding yours, but not the continent-scale thing you may have read about. Irrigation is the lever that matters here: three months of dry-season watering raised Argentine nest counts by 54% in one study.
What a technician actually does on an ant visit
- Identify the species before anything is opened. Node count, size, colour, and the smell of a crushed worker. Everything downstream depends on this, and a technician who starts spraying before identifying is guessing.
- Follow the trails to find out where they enter, not just where they are. Ants run along edges: sill plates, pipe penetrations, the underside of countertop overhangs, branches touching the roof. The entry point is usually several feet from the activity you noticed.
- Test the bait before committing to it. NC State recommends placing a small amount where ants are actively trailing and watching for a few minutes. No interest means wrong bait; try another. This step takes five minutes and decides whether the next two weeks work.
- Place bait at the activity, in enough quantity, out of reach of children and pets. Never on a food preparation surface, never where it will get wet. Large colonies need several stations. Bait stays in place for three to four days after feeding stops.
- Treat the exterior with a non-repellent, not a repellent barrier. Applied to the foundation band and harbourage, so ants that never find a station still carry the active home.
- Deal with what is feeding them. Honeydew-producing aphids and scale on shrubs touching the house, a leaking hose bib, pet food left down overnight, mulch banked against the siding. Ant pressure is an outdoor problem before it is an indoor one.
- Come back. UC IPM puts the timeline at five to ten days before numbers drop, and bait aged by heat, rain and sun needs replacing. A single visit against an established colony is optimistic.
If you have already sprayed the area, say so when you book. A technician can work around a contaminated surface, but only if they know it was treated. It is the single most useful thing you can tell them, and the thing people leave out because they assume it will sound like they made the problem worse. It usually did, and that is fine, it is recoverable.
What does not work, and why
| Remedy | Why it fails | Do this instead |
|---|---|---|
| Aerosol spray on the trail | Kills foragers, repels the rest, contaminates any bait nearby | Wipe the trail with soapy water, then bait |
| Homemade borax at full strength | Too concentrated; the ant dies before reaching the nest | Under 1% borate, or a commercial bait |
| Vinegar, citrus, peppermint, cinnamon | Erases the pheromone trail for a few hours; no effect on the colony | Useful for cleaning up, not for control |
| Diatomaceous earth indoors | Ants route around visible dust; useless once damp | Seal the gap they are using |
| Boiling water on a fire ant mound | Rarely reaches the queen; kills the surrounding lawn; scalding risk | Broadcast granular bait |
| Killing the ants and stopping there | Roughly 1% of foragers sustains the nest | Let them carry bait home |
Where DIY genuinely works
Not every ant problem needs a technician, and it is worth being straight about which ones do not. A single trail of odorous house ants to a spill under the toaster, caught in the first week, will usually resolve with a supermarket gel bait, a sealed crack and two weeks of patience. UC IPM's own emergency sequence is: find and remove what they are feeding on, wipe the trails with soapy water, caulk the entry, put out bait, keep cleaning up, and skip the indoor spray entirely.
The cases where that stops being enough are fairly predictable. Ants in more than one room, or on more than one floor, usually mean an interior nest rather than an outdoor colony foraging inside. Trails that return within days of a successful bait-out point at a colony large enough or fragmented enough to need the perimeter handled too. And two species are genuinely different jobs.
Carpenter ants are a moisture investigation with an insect attached. Finding the nest matters more than the product, because the parent colony is often outside in a tree or stump with a satellite in a wall void kept damp by a leak. Treating the trail without finding the water gets you a repeat visit next spring. Our guide to telling carpenter ants from termites covers the identification, which is the part people get wrong first.
Fire ants are an outdoor turf job with a broadcast bait, not a spot treatment, and worth taking seriously in this region: all 46 South Carolina counties sit inside the USDA imported fire ant quarantine. Mound-by-mound treatment makes a lawn look better for two weeks while the colonies simply relocate.
If you want the whole thing handled, that is what our ant control service is: identification, species-matched baiting, a non-repellent exterior, and the follow-up visit that most DIY attempts never get to.
The short version
- Baits, mostly. Fipronil, hydramethylnon, abamectin and borates are the four actives you will meet.
- Killing foragers achieves almost nothing. As few as 1% of them can feed the entire nest.
- Repellent versus non-repellent decides the outcome. Repellents detour ants; non-repellents get carried home.
- Never spray a baited area. It contaminates the bait and repels the ants that were about to take it.
- Borate baits must be under 1%. Strong homemade mixes kill the messenger.
- The bait must match the species and the season, which is why identification comes before any product.
- Expect five to ten days before numbers fall, and more ants at the station before fewer in the kitchen.
Sources: NC State Extension, Tips for Effective Ant Baiting (how baits reach the colony, bait testing, placement, spray contamination); University of California IPM, Pest Notes: Ants and its species baiting guides (the 1% foraging figure, bait actives, borate concentration, the five-to-ten-day timeline, species food preferences). Argentine ant colony structure in the Carolinas follows Buczkowski, Vargo & Silverman 2004, Molecular Ecology 13:2235; the irrigation figure follows Menke & Holway 2006.
Frequently Asked Questions
Most ant work is done with baits built on one of four actives: fipronil, hydramethylnon, abamectin, or a borate such as boric acid. Outside, a non-repellent liquid, commonly fipronil, is applied to the foundation band so ants carry it back without detecting it. The same actives appear in consumer products; the difference is matching the bait to the species and placing it correctly.
Because the ants you can see are not the problem. UC IPM notes that as few as 1% of a colony's foragers can feed the queens and larvae in the nest. A bait has to be slow enough for the worker to get home and share it, so the active reaches the brood and the queens. Anything that kills her on the counter fails at the only job that mattered.
No. NC State warns that spraying a baited area contaminates the bait and repels ants away from it, and most consumer aerosols are repellent, which scatters the colony rather than killing it. Wipe trails with soapy water if you want them gone from view, and tell the technician which areas you have already sprayed.
Yes, as a stomach poison, but only at low concentrations. UC IPM's figure for a liquid borate bait is 0.5 to 1% borate in sugar water. Most homemade recipes are far stronger, which kills the forager before she returns to the nest and leaves the colony untouched. If ants are dying on the counter rather than carrying bait away, the mix is too strong.
Expect five to ten days before ant numbers noticeably drop, and often more ants at the bait in the first day or two as the colony recruits to it. That surge is the treatment working. Bait is usually left in place for three to four days after feeding stops, and an established colony normally needs a follow-up visit.
Usually one of three reasons: the bait was wrong for that species, so it was never eaten; the colony is outdoors and nothing changed outside, so new foragers keep arriving; or something is still feeding them, such as aphids on shrubs against the house, pet food, or a leak. Argentine ants in particular form multi-queen networks that can span adjoining properties, so an untreated neighbouring yard will keep reseeding yours.
A single trail to an obvious food source, caught early, often clears with a gel bait, a sealed entry point and two weeks of patience. Call someone when ants appear in more than one room, when trails return within days of baiting, or when you are dealing with carpenter ants or fire ants, which need a nest hunt and a broadcast turf treatment respectively rather than a spot product.
Photo credits: Thmazing, public domain, via Wikimedia Commons; USDA APHIS PPQ, CC BY 3.0 US, via Wikimedia Commons; Bradley Rentz, CC BY-SA 4.0, via Wikimedia Commons; Nwbeeson, CC BY-SA 4.0, via Wikimedia Commons.