I found this statement on the Ohio State Univ website Biology of Subterranean Termites in the Eastern United States:
Termites prefer to feed on soft, spring growth wood rather than hardwoods and woods rich in natural chemical protectants. Some woods (e.g., redwood, cypress, juniper) are less preferred by termites, but no wood is completely immune to attack. In general, termites prefer cellulose that is easy to obtain. For example, in laboratory studies, they prefer in this order: loose cellulose fibers > paper > cardboard > softwood blocks > hardwood blocks. In the field, preference for a particular cellulose resource is likely determined by its availability, size, texture, and the nutritional demands of the termite colony. As termites break off wood fibers, they swallow the small fibers, which then undergo complete digestion by protozoans, bacteria, and enzymes in the termite hindgut.
