When baiting for ants that are foraging indoors, especially unicolonial ants like the Argentine (Linepithema humile), odorous house (Tapinoma sessile, or OHA) or ghost ant (T. melanocephalum) species, PMPs often choose to bait indoors only. This approach has its place and can be effective, but if you find that you’re often going back and performing multiple callbacks, it may be a good idea to consider baiting outside. Baits are designed to be attractive, and when you bait inside of a structure, you lure ants inside. Exterior baiting is an overlooked strategy that can be extremely effective.
The species mentioned above typically have many different satellite colonies, either inside or around the exterior of a structure. By taking your baiting approach outdoors, you provide an attractive food option much closer to their nests, thus moving more bait into colonies more quickly than if they had to forage all the way indoors (ghost ants or OHA nesting inside being exceptions). You also are providing a food source outside, which is usually why they were foraging indoors in the first place.