How long do ant baits take to work?

Why bait is meant to be slow

A bait that killed ants on contact would kill the foragers before they got back to the nest, and the colony would carry on untouched. Ant bait is deliberately slow-acting so that foragers have time to carry it home and pass it on to the workers, larvae and queen.

That delay is the whole mechanism. If you're seeing ants feeding on bait and walking away, that's it working, not failing.

What you'll see, and when

The first day or two usually looks worse. Foragers find the bait, recruit others, and the trail gets busier. It's tempting to wipe it away or reach for the spray at this point. Don't - both interrupt the delivery.

After that, activity should thin out steadily. Smaller household colonies often fade within days, and larger ones can take a couple of weeks. A colony that's part of a much bigger network - which is how Argentine ants behave - can keep sending replacements for longer.

What slows it down

• Spraying near the bait, which makes ants avoid the area
• Wiping the trail away while bait is still being collected
• Bait that has dried out or gone stale
• Plenty of competing food nearby, so the bait isn't the best option on offer
• Bait placed away from the trail rather than on or beside it
• Heavy rain washing outdoor bait away

If nothing has changed after two weeks

Ants' food preferences shift - at times they want sugars, at others protein or fat - so a bait that was ignored may simply be the wrong type for the moment. Trying a different type of bait is a reasonable next step.

If trails are still heavy after a second attempt, the nest may be somewhere you can't reach, or you may be dealing with a large connected colony rather than a single nest. At that point it's worth having the species identified and the nest located rather than putting down more bait.