Termites foraging for food above ground protect themselves with shelter tubes, sometimes called mud tubes. Worker termites build these tubes from particles of soil and wood that are held together by salivary sectretions and fecal matter. The tubes may be thinly constructed or large and thick-walled to accomodate larger number of termites as they move between the colony and the food source. Construction material can also be found lining the wood being attacked and aids in identifying termite-damaged wood.
Shelter tubes are often used to bridge masonry or other obstacles, allowing termites access to a food source (wood) above ground. Damage caused by termites can be found in dead trees and brush which are the natural sources of termites. When the land is cleared of this material and houses are built, termites then infest the homes and structures that replaced their natural food source.
The average shelter tube measures between 1/4" and 1/2", but can get much larger, based on the time the infestation has gone undetected. If the shelter tube is in use, the interior of the tube will be moist and there will be Worker and Soldier termites present within the tube. If a section of the tube is broken, the Workers will immediately begin to repair the breach to avoid losing essential moisture and to help prevent attack from predators.