You searched for: “xylophagy
The eating of wood as is done by certain insects; such as, termites.

Many xylophagous insects have symbiotic protozoa and/or bacteria in their digestive system which assist in the breakdown of wood cellulose.

The cellulose, or inert carbohydrate which is the chief constituent of the cell walls of plants and of wood, cotton, hemp, paper, etc. that exist in a termite's food is digested by myriads of flagellated protozoans living in the termite's digestive tract.

Without the protozoans in the termites digestive areas, the termites would starve because the cellulose could not be digested without the protozoans.

Other organisms, especially among the groups feeding on decaying wood, apparently derive much of their nutrition from the digestion of various fungi that are growing within the wood fibers.