“Western subterranean termites are highly destructive to douglas fir and other common timbers used in the construction of a building. They can rapidly eat out the internal sections of structural timbers – devouring mainly the spring wood, and preferring to leave the harder summer wood sections. As a result, infested timbers are often left as a thin shell with a honey-comb of layered hollow sections packed with moist soil.”
This and other fascinating termite facts such as “did you know that a termite queen can live up to 25 years? are found in this article.
A WSU publication can be found here