What unique behavior characterizes subterranean termites?

Subterranean termites are indeed characterized by their construction of tubes made from saliva, soil, and chewed wood. This behavior is crucial for their survival as it enables them to travel between their underground colonies and above-ground wood sources while protecting themselves from predators and desiccation. The tubes act as a safe highway that provides moisture and shelter from open air, which is essential for these insects, as they are highly sensitive to environmental conditions.

The other options fail to capture important aspects of subterranean termite behavior. For instance, while some species may exhibit preferences for hardwood, they are not limited to only attacking hardwoods; they can infest a wide range of wood types, including softwoods. The production of sound to attract mates is not a characteristic behavior of subterranean termites, as many termites communicate through chemical signals rather than auditory means. Lastly, subterranean termites rely heavily on their colony for survival; they do not have the means to survive individually outside of the colony structure, as they depend on the social structure for care and sustenance. Thus, the behavior of constructing tubes is a distinctive and essential aspect of subterranean termite life.