As of mid-September 2026, in my 1966 ranch house here in Riverside, the reflex hasn’t changed since I moved in back in ’94: ants show up along the windowsill or across the kitchen counter, and the can of spray comes out. One pass down the trail, the visible ants curl up and die, and everybody figures that’s the end of it — job done, coffee’s still hot.
It isn’t. Right now the ground out here is bone-dry, the Santa Ana winds have been pulling every bit of moisture out of the yard for weeks, and the ants are doing what they do every September before the first real rain finally breaks the cycle — heading straight for water, which means the kitchen sink and the bathroom. Spray that trail and by the next morning there’s another one three feet over, coming out of a different crack in the stucco.
What UC’s Statewide IPM Program says
The UC Statewide IPM Program, which has spent decades studying how ants actually behave in California homes, put it plainly: “Use baits outdoors to control the ant colony. Pesticide sprays only provide temporary control and may not be safe to use indoors.” That’s the whole problem with the reflex — you’re treating the ants you can see, not the colony that sent them.
Why the spray doesn’t finish the job
Most sprays only kill the ants that physically touch them, and there are always more coming from behind the baseboard that never make contact. Some sprays act more like a repellent than a killer, which doesn’t kill the ants so much as nudge them toward a different food source for a while — so the trail moves instead of disappearing. Bait works the opposite way: a worker carries a slow-acting poison back to the nest, where it eventually reaches the queens and the rest of the colony, which is the only part of this that actually matters. Spraying indoors doesn’t even stop more ants from coming in — it just kills the ones already inside for that one afternoon.
What it costs you in patience
Here’s the part that sends people back to the spray can in the first place: bait doesn’t work overnight. It can take 5 to 10 days to see fewer ants, and that week of watching them still cross the counter feels like failure. It isn’t. It means the workers are still out there hauling poison back to a nest you can’t see, which is the only way this ends instead of just relocating to the next window.
What to do instead
- Skip the spray on the trail itself — spraying near bait contaminates it and repels ants from the exact spot you’re trying to treat, so pick one method and stick with it.
- Put bait where you’re actually seeing activity — inside the cabinet, along the counter edge, wherever the trail runs — not scattered around the whole kitchen.
- Find where they’re getting in and seal it with caulk once the bait has had its week to work.
- If the house is old enough that you can’t reasonably caulk every gap — and a 1966 slab-and-stucco house has plenty — let the bait carry the load. “Blocking entry points is the best way to permanently keep ants out,” but baiting fills in for the cracks you’ll never fully catch.
- If you end up calling someone, ask specifically for bait placement and spot treatment, not a perimeter spray or a monthly service contract — that routine is exactly what the same research says doesn’t touch the colony.
When you do call, describe it as an indoor ant trail needing bait placement and entry-point sealing, not a general pest spray, and it doesn’t hurt to snap a photo of the trail and where it disappears into the wall first, before anyone shows up quoting you a monthly perimeter add-on you didn’t ask for.
Sources
- Ants
- Tips for Effective Ant Baiting | NC State Extension Publications
- Indoor Ant Control
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