What pest is indicated by timber that has extensive galleries which are clean and smooth?

The pest indicated by timber that has extensive galleries which are clean and smooth is actually the powder post beetle. These pests are known for creating very fine, smooth galleries as they bore into the wood. The clean and smooth appearance results from their feeding habits, which leave behind a fine, dust-like frass. Unlike carpenter ants, which typically create rougher galleries filled with debris, powder post beetles are more meticulous in their excavations.

Termites also create galleries but often leave behind more evidence of wood destruction and tend to be less tidy than powder post beetles. Wood-boring beetles could be misleading, as the term encompasses a variety of beetles that excavate wood, but their specific characteristics vary. Carpenter ants do not create extensive smooth galleries in the same way that powder post beetles do, as they prefer to clear out existing decay rather than creating clean, smooth tunnels.

Therefore, the characteristics of the galleries in question strongly align with the behavior of powder post beetles.