Which ant species almost always has its colony inside structures?

The Pharaoh ant is known for its behavior of nesting primarily within human structures. This species prefers warm, humid environments and typically establishes colonies in places like wall voids, behind baseboards, and other hidden areas within buildings. Their nesting habits make them a common pest in residential and commercial settings, as they can easily thrive in the conditions provided by human habitation.

In contrast, while carpenter ants also have an affinity for structures, they primarily nest in wood, often causing structural damage. Fire ants tend to establish outdoor mounds and are less likely to reside primarily within structures, focusing on open fields or disturbed areas. Odorous house ants can invade homes but are less specifically tied to nesting inside, as they can also form nests outdoors and do not have the same level of preference for indoor environments as Pharaoh ants do.