Mud tubes or shelter tubes are proof of termite infestation, but their absence does not necessarily mean that a structure is free of termites. The insects may reach sills and other wood members through cracks or voids in the foundation wall, under the outside stucco, or from earth-filled porches, steps, terraces, or patios. You can break open tubes to determine if termites are still active inside. Termites often rebuild damaged tubes, another indication of continued activity. Old tubes are dry and will crumble easily.
Subterranean termites construct four types of tubes or tunnels.
Workers are sterile and usually hidden within infested wood. However, the absence of finding live termites does not mean that they are not present in the structure. Buckling paint or tiny holes on wood. Wood may appear crushed at structural bearing points. Pick and probe the surface of an infested piece of wood with a pen knife and you will find tunnels running parallel to the wood's grain.