Where do Subterranean Formosan Termites primarily build their colonies?

Subterranean Formosan Termites primarily build their colonies in soil, which provides the moisture and protection they need to thrive. These termites excavate tunnels and create elaborate nests underground. The soil also allows them to access wood easily, as they typically tunnel through the ground to reach wooden structures and materials above. The nesting behavior in soil helps protect them from predators and environmental conditions that would be unfavorable for their survival.

While the other options suggest various habitats, they do not align with the known behavior and biology of Formosan Termites. They do not dwell underwater, as they require the soil for their colonies rather than an aquatic environment. Colonizing tree trunks is also not their primary behavior; they may infest trees but do not establish their main colonies there. Building nests on the surface of wood is not a characteristic of subterranean termites; rather, they work from below the ground level, accessing wood by tunneling from their colonies in the soil.