Why Do Ants Keep Coming Back After You Spray?

Because you killed the wrong ants. Iowa State's guidance on household ants explains that sprays may impact only the small portion of the colony that is out looking for food, while queens and other colony members safely hidden in their nests are not affected. University of Minnesota puts it the same way: killing foraging workers has little effect because just a small percentage of ants are out of the nest at any given time. The counter looks clean for a day. The nest sends the next shift.

Wiping the trail has the same limit. Penn State suggests wiping ant trails with soapy water or a vinegar and water solution, which erases the pheromone trail Minnesota describes them following. It does not touch the nest, so a new trail appears.

It can. Utah State's odorous house ant fact sheet describes budding: inadequate insecticide applications causing a colony to split and new subcolonies to form. UC IPM says the same for Pharaoh ants, where budding may be triggered by insecticide sprays applied to trailing workers. Washington State describes odorous house ants as polydomous and polygynous in urban settings, meaning many nests and many queens, which is exactly the kind of colony that responds to a repellent spray by spreading out. One trail in the kitchen becomes three trails in three rooms.

Usually outside. Colorado State says most ants that occur within homes originate from outdoor colonies. Iowa State says odorous house ants commonly nest outdoors in soil under stones, logs, mulch, and debris, and will also nest indoors in wall and floor voids. Penn State says most pavement ant colonies are under sidewalks, building slabs, and large rocks, and that they enter through cracks in foundation walls and interior slabs.

Rain sends them in. UC IPM notes odorous house ants invade homes most often during rainy weather because their natural food supply, honeydew from insects on plants, is washed off the vegetation. The kitchen is the nearest replacement.

Know which ant it is. Wisconsin describes the odorous house ant as dark brown to black and about an eighth of an inch. If the ants are noticeably bigger, three eighths to half an inch and black, Minnesota's carpenter ant page applies, and that is a nest-in-wood problem with its own guide.

Products the ants do not notice. Utah State explains that ants do not detect non-repellent insecticides, so they keep traveling over them and drag the chemical back to the nest, where it is transferred around the colony. Baits work through the colony's own food sharing. NC State says most ant baits are slow-acting, and that workers carry small quantities back to the nest where they feed it to the queens, brood, and other workers. Colorado State calls the process trophallaxis.

One rule follows from this. NC State: spraying the ants or the area baited will contaminate the bait and likely repel the ants from the area. If you have already sprayed, wait before baiting, and do not spray again.

Identify the species and find the trails. Odorous house ant, pavement ant, or carpenter ant changes the product and the placement.

Non-repellent perimeter treatment at the foundation, entry points, and the outdoor nest sites we can locate.

Bait placed on the active trails, indoors and out, matched to what the colony is feeding on at the time.

No spraying over the bait, no fogging.

Written 90-day guarantee. Ant treatment carries a 90-day written guarantee, and the quote is free and in writing before we start.

Baits take time on purpose. Colorado State says the effects of ant baiting usually start to become apparent within a week or two, and Minnesota warns that baits act slowly and may take several weeks to several months to eliminate a colony, which is the reason for the 90 days. You may see more ants at the bait for the first day or two. That is the bait working; they are carrying it home.

Close the gaps and move the mulch. Penn State's ant IPM guidance is to seal cracks and crevices around windows, doors, and pipes with caulk, keep vegetation and mulch at least 6 inches from the base of the house, and keep tree branches and shrubbery from touching the house because ants use them as runways. Cornell's IPM program says the same about cutting vegetation at least 6 inches off the structure. Inside, Colorado State's advice is to eliminate the food and water sources that attract them: wipe the counter, seal the sugar, rinse the recycling.