Subterranean termites are insects known for their destructive feeding habits on wood and other cellulose-based materials. As their name suggests, they maintain their primary colony and nest within the soil for protection and resources. While fundamentally ground-dwelling, they can operate above ground for extended periods under specific, controlled conditions. They achieve this by constructing specialized structures that bridge the gap between their underground home and the wood in a structure.
The Biological Necessity of Soil Contact
Subterranean termites depend on a high-moisture environment to survive. Their bodies are highly susceptible to desiccation, meaning they dry out rapidly when exposed to open air. This vulnerability is the primary reason the central colony, which houses the queen, eggs, and the majority of the population, is located deep underground.
The soil acts as a reservoir, providing the consistent moisture and humidity necessary for the termites to regulate their body water content. Without this connection to damp soil, the colony cannot sustain its life cycle or population size. This constraint dictates their foraging behavior, forcing them to maintain a physical link to the ground as they search for food.
Constructing Sheltered Pathways
To access food sources above ground, subterranean termites construct protective structures known as mud tubes or shelter tubes. These tunnels are built from a mixture of soil particles, wood fragments, saliva, and feces, which acts as a binding agent. The tubes serve as a secure highway, allowing workers to travel between the moist soil and the dry wood of a structure.
The primary function of the mud tube is to create an enclosed, high-humidity microclimate that prevents the termites from drying out during their journey. This protective barrier also shields the workers from light and predators, such as ants. Workers construct different types of tubes for specific purposes.
Types of Tubes
Workers construct working tubes, which are busy, permanent travel routes, and exploratory tubes, which are thinner and used by scouting termites to search for new food sources. Mud tubes often run along foundation walls, concrete piers, and plumbing lines to bridge non-wood materials and reach the structure above. Termites may also build “drop tubes” that hang from overhead wood to re-establish a connection with the ground.
Survival Limitations When Cut Off From the Ground
While termites can be found actively feeding in wood high above the ground, their survival remains tied to the moisture source below. If a section of the mud tube is broken, isolating a group of workers within a wall or ceiling, those termites are immediately at risk. The isolated workers will quickly perish due to desiccation unless the infested wood has an alternative, high-moisture content.
For isolated subterranean termites to sustain a long-term infestation without a soil connection, the wood must have a moisture content of 30% or more. Standard structural wood has a much lower moisture content, which is insufficient for long-term survival. Isolated termites rapidly lose body weight and die because the water obtained from feeding cannot compensate for the water lost through their skin.
The main colony cannot establish permanently above ground if the soil connection is severed. This is only possible if a secondary moisture source, such as a plumbing leak or a faulty roof, is present to create a perpetually damp environment.
Subterranean Versus Drywood Termites
The presence of termites above ground often leads to confusion between subterranean termites and drywood termites, which have fundamentally different nesting habits. Subterranean termites require soil contact and are primarily identified by the presence of their mud tubes. They also pack their feeding galleries with soil and mud to maintain the necessary humidity within the structure.
Drywood termites do not require any connection to the soil or external moisture to survive. They establish colonies entirely within the dry wood they consume, such as structural lumber or furniture. This species does not construct mud tubes, making their presence harder to detect until significant damage has occurred.
The clearest sign of a drywood infestation is the accumulation of frass, which are distinctive, hard, pellet-like fecal droppings pushed out of small kick-out holes. Subterranean termites do not produce this type of frass because they use their excrement to construct their tubes. Distinguishing between these two types is important, as subterranean colonies are larger and cause more rapid structural damage, requiring different treatment strategies.