Subterranean termites generally nest in the ground and the workers come to the surface to find cellulose, a wood product, which they eat and then return to the nest to feed the others. When termites exit from the ground to find wood they build shelter tubes which they travel through. They keep the interior of these tubes damp as they need moisture to survive. The picture on the left shows a termite shelter tube on a block foundation wall in a crawl area. The shelter tube runs up the block and then splits and goes in two directions. The termites may continue to build a tube until they find wood to enter and feed on.
When termites find unprotected wood they will begin to tunnel through the wood eating the cellulose from the interior of the wood. Even as they are tunneling through wood they still will continue to build shelter tubes around themselves inside the wood. In the picture to the right termites are in a main girder in the crawl space of a home. At the bottom of the girder you can see shelter tubes hanging from the bottom of the girder. Sometimes the termites can build successfully build a tube from the bottom of a girder or other wood member back to the ground making a free standing shelter tube.
Shelter Tubes on Bottom of Girder
Rot Fungi Growth on Floor Joists
In most homes the substructure is made of wood and in most cases the wood is not pressure treated. If the moisture levels rise above acceptable levels in untreated lumber the wood then may be attacked by a wood destroying organism, rot fungi. This is a plant that begins to grow on the surface of the wood, the roots bury into the wood and may eat the cellulose from the wood causing deterioration to occur. In the picture to the left brown rot fungi was observed on the floor joists. In this crawl space a contractor made repairs to approximately 20 floor joists and steps had to be taken to reduce the high moisture levels in the wood.